The Response of Maize Physiology under Salinity Stress and Its Coping Strategies

*Shazia Iqbal, Sajid Hussain, Muhammad Abdul Qayyaum, Muhammad Ashraf and Saifullah*

### **Abstract**

Maize is a cross-pollinated, polymorphic plant in nature. It is commonly a moderately salt-sensitive crop. Salinity stress is the main abiotic factor that arrests the physiological characteristics and plant growth of a maize plant. It causes the osmotic effect, associated with an increase in phytotoxic ions, oxidative stress by increased reactive oxygen species (ROS) production, and ionic effect in the cytosol. These salinity effects hinder the maize plant's physiological processes such as respiration, photosynthesis, transpiration, stomatal functioning, hormone regulation, and functioning, seed germination, and dormancy and water relation with plants and ultimately reduce the plant growth and yield. However, the physiology of maize subjected to salinity shows various responses that depend on the genetic responses and growth stages. Maize plant undergoes many physiological changes and adapts some mechanism internally to cope with salinity stress. Numerous mitigating strategies such as application of chemicals, application of plant growthpromoting rhizobacteria (PGPR), application of hormones, and use of genetic and molecular techniques are used to handle salinity. This chapter will cover the effect of salinity on maize growth, its physiology, and physiological adaptations of maize plants with management strategies.

**Keywords:** *Zea mays* L., salinity, physiology, genetic and molecular techniques, antioxidants

### **1. Introduction**

Soils with an excessive amount of soluble salts or exchangeable sodium in the root zone are termed salt-affected soils. Owing to limited rainfall and high evapotranspiration demand, coupled with poor soil and water management practices, salt stress has become a serious threat to crop production in arid and semi-arid regions of the world [1, 2]. Although the general perception is that salinization only occurs in arid and semi-arid regions, no climatic zone is free from this problem [3]. More than 800 million hectares of land worldwide is affected by either salinity (397 million hectares) or sodicity (434 million hectares) [4–6].

Maize (*Zea mays* L.) is the third most important cereal crop after rice and wheat and is grown under a wide spectrum of soil and climatic conditions. It is an important C4 plant from the *Poaceae* family and is moderately sensitive to salt stress;

nonetheless, wide intraspecific genetic variation for salt resistance exists in maize. According to the biphasic model of salinity-induced growth reduction [7], osmotic stress during the first phase and ion toxicity during the second phase are responsible for reduced growth in cereals, specifically wheat. The same model for salinityinduced growth reduction in maize was confirmed by [8], but ion toxicity and the associated growth reduction can occur, to a small extent, in the first phase in maize. The sensitivity of maize to salinity is associated with higher accretion of Na<sup>+</sup> in the leaves. A saline level of more than 0.25 M NaCl damages maize plants and may stunt growth and cause severe wilting [9].

stress during germination delays the start, reduces the rate, and enhances the dispersion of germination events [23–25]. It is important to note that germination and early seedling growth are more sensitive to salinity than later developmental stages [26]. Salt stress influences seed germination primarily by sufficiently lowering the osmotic potential of the soil solution to retard water absorption by seeds, by causing sodium and/or chloride toxicity to the embryo or by altering protein synthesis. Hyper-osmotic stress and toxic effects of sodium and chloride ions on germinating seeds in a saline environment may delay or inhibit germination [25, 27]. However, in maize, it is sodium toxicity and not chloride toxicity that is the major

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

**3.2 Salinity stress response on vegetative, reproductive growth and grain yield**

Salt stress may also displace calcium from plasma membrane binding sites, thus causing membrane leakiness as a primary cellular response to salt stress [35]. However, it is interesting to note that if salt stress influences the integrity of the plasma membrane, then the cell wall acidification process, which is partially dependent on adenosine triphosphate-driven outward pumping of protons across the intact plasma membrane, may also be affected [36]. Acidification of the apoplast is the major requirement for increasing cell wall extensibility, which controls extension growth [37]. In this regard, cell wall proteins such as expansions are of great interest. Expansions, wall-loosening enzymes located within the apoplast of the elongation zone of leaves [38], regulate cell elongation. The assimilate supply to growing tissues is not limited during the first phase of salt stress [39], suggesting that photosynthesis is not responsible for any growth reduction in maize during this phase. Salinity-induced growth reduction in maize is caused by suppressed leaf initiation, expansion, and internode growth and by increased leaf abscission. In maize, suppression of expansion growth by salinity is principally caused by reduced

apoplastic acidification and activity of wall-loosening enzymes.

In salt-affected soils, excessive buildup of sodium and chloride ions in the rhizosphere leads to severe nutritional imbalances in maize due to strong interference of these ions with other essential mineral elements such as potassium, calcium, nitrogen, phosphorus, magnesium, iron, manganese, copper, and zinc [40, 41]. Generally, salt stress reduces the uptake of nitrogen, potassium, calcium, magnesium, and iron [42]. For maize, sodium is the principal toxic ion interfering with potassium uptake and transport, leading to disturbance in stomatal modulations and causing water loss and necrosis. Competition between potassium and sodium under salt stress severely reduces potassium content in both leaves and roots of maize [19] and reduces potassium content by up to 64% in the symplast of

expanding tissues under salt stress. Moreover, salt stress not only reduces potassium uptake rates but, to a greater extent, disturbs potassium translocation from root to shoot tissues in maize, leading to lower potassium shoot contents than root contents. Reduced leaf expansion with reduced calcium contents in expanding shoot tissues in maize is due to reduced transport in a saline environment; some calcium is

Although the root is the first organ exposed to salt stress, shoots are more sensitive to salt stress than roots [7]. Salinity promotes the suberization of the hypodermis and endodermis, and the Casparian strip develops closer to the root tip than in non-saline roots [28]. Salinity reduces shoot growth by suppressing leaf initiation and expansion, as well as internode growth, and by accelerating leaf abscission [29–31]. Salt stress rapidly reduces the leaf growth rate due to a reduction in the number of elongating cells and/or the rate of cell elongation. As a saltsensitive crop, shoot growth in maize is strongly inhibited in the first phase of salt

problem in the second phase of salt stress.

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

stress [32–34].

**43**

### **2. Salinity stress**

Sodium is the main toxic ion interfering with potassium uptake and thus disturbs stomatal undulations causing severe water loss and necrosis in maize; a reduction in potassium content in the leaf symplast of maize has been reported under saline conditions. High osmotic stress due to low external water potential, ion toxicity by sodium and/or chloride, and imbalanced nutrition due to interference with the uptake and transport of essential nutrients are three potential effects of salt stress on crop growth. The latter may not have an immediate effect because plants have some nutrient reserves which can be remobilized [10, 11]. Osmotic stress is linked to ion accumulation in the soil solution, whereas nutritional imbalance and specific ion effects are connected to ion buildup, mainly sodium and chloride, to toxic levels which interferes with the availability of other essential elements such as calcium and potassium [12]. Toxic levels of sodium in plant organs damage biological membranes and subcellular organelles, reducing growth and causing abnormal development before plant mortality [13, 14]. Several physiological processes such as photosynthesis, respiration, starch metabolism, and nitrogen fixation are also affected under saline conditions, leading to losses in crop productivity.

Moreover, salt stress also induces oxidative damage to plant cells with overproduction of reactive oxygen species in maize [15]. The ability of plants to survive and produce harvestable yields under salt stress is called salt resistance. Salt resistance is a complex phenomenon, and plants manifest a variety of adaptations at subcellular, cellular, and organ levels such as stomatal regulation, ion homeostasis, hormonal balance, activation of the antioxidant defense system, osmotic adjustment, and maintenance of tissue water status to grow successfully under salinity [16–20]. An integrated approach encompassing conventional breeding together with marker-assisted selection, biotechnology, exogenous use of growth regulators/ osmoprotectants, and nutrient management may be needed for successful maize cultivation on salt-affected soils [21–23].

### **3. The response of salinity stress on maize plant physiology**

Salt stress affects the growth and development of maize; however, the response of plants varies with the degree of stress and crop growth stage. Short-term exposure of maize plants to salt stress influences plant growth, owing to osmotic stress in the first phase of salt stress without reaching toxic sodium concentrations.

### **3.1 Salinity stress response on seed germination**

Seed germination is the most critical stage in a seedling establishment which determines the success of crop production on salt-affected soils. Generally, salt

### *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

stress during germination delays the start, reduces the rate, and enhances the dispersion of germination events [23–25]. It is important to note that germination and early seedling growth are more sensitive to salinity than later developmental stages [26]. Salt stress influences seed germination primarily by sufficiently lowering the osmotic potential of the soil solution to retard water absorption by seeds, by causing sodium and/or chloride toxicity to the embryo or by altering protein synthesis. Hyper-osmotic stress and toxic effects of sodium and chloride ions on germinating seeds in a saline environment may delay or inhibit germination [25, 27]. However, in maize, it is sodium toxicity and not chloride toxicity that is the major problem in the second phase of salt stress.

### **3.2 Salinity stress response on vegetative, reproductive growth and grain yield**

Although the root is the first organ exposed to salt stress, shoots are more sensitive to salt stress than roots [7]. Salinity promotes the suberization of the hypodermis and endodermis, and the Casparian strip develops closer to the root tip than in non-saline roots [28]. Salinity reduces shoot growth by suppressing leaf initiation and expansion, as well as internode growth, and by accelerating leaf abscission [29–31]. Salt stress rapidly reduces the leaf growth rate due to a reduction in the number of elongating cells and/or the rate of cell elongation. As a saltsensitive crop, shoot growth in maize is strongly inhibited in the first phase of salt stress [32–34].

Salt stress may also displace calcium from plasma membrane binding sites, thus causing membrane leakiness as a primary cellular response to salt stress [35]. However, it is interesting to note that if salt stress influences the integrity of the plasma membrane, then the cell wall acidification process, which is partially dependent on adenosine triphosphate-driven outward pumping of protons across the intact plasma membrane, may also be affected [36]. Acidification of the apoplast is the major requirement for increasing cell wall extensibility, which controls extension growth [37]. In this regard, cell wall proteins such as expansions are of great interest. Expansions, wall-loosening enzymes located within the apoplast of the elongation zone of leaves [38], regulate cell elongation. The assimilate supply to growing tissues is not limited during the first phase of salt stress [39], suggesting that photosynthesis is not responsible for any growth reduction in maize during this phase. Salinity-induced growth reduction in maize is caused by suppressed leaf initiation, expansion, and internode growth and by increased leaf abscission. In maize, suppression of expansion growth by salinity is principally caused by reduced apoplastic acidification and activity of wall-loosening enzymes.

In salt-affected soils, excessive buildup of sodium and chloride ions in the rhizosphere leads to severe nutritional imbalances in maize due to strong interference of these ions with other essential mineral elements such as potassium, calcium, nitrogen, phosphorus, magnesium, iron, manganese, copper, and zinc [40, 41]. Generally, salt stress reduces the uptake of nitrogen, potassium, calcium, magnesium, and iron [42]. For maize, sodium is the principal toxic ion interfering with potassium uptake and transport, leading to disturbance in stomatal modulations and causing water loss and necrosis. Competition between potassium and sodium under salt stress severely reduces potassium content in both leaves and roots of maize [19] and reduces potassium content by up to 64% in the symplast of expanding tissues under salt stress. Moreover, salt stress not only reduces potassium uptake rates but, to a greater extent, disturbs potassium translocation from root to shoot tissues in maize, leading to lower potassium shoot contents than root contents. Reduced leaf expansion with reduced calcium contents in expanding shoot tissues in maize is due to reduced transport in a saline environment; some calcium is

nonetheless, wide intraspecific genetic variation for salt resistance exists in maize. According to the biphasic model of salinity-induced growth reduction [7], osmotic stress during the first phase and ion toxicity during the second phase are responsible for reduced growth in cereals, specifically wheat. The same model for salinityinduced growth reduction in maize was confirmed by [8], but ion toxicity and the associated growth reduction can occur, to a small extent, in the first phase in maize. The sensitivity of maize to salinity is associated with higher accretion of Na<sup>+</sup> in the leaves. A saline level of more than 0.25 M NaCl damages maize plants and may stunt

Sodium is the main toxic ion interfering with potassium uptake and thus disturbs stomatal undulations causing severe water loss and necrosis in maize; a reduction in potassium content in the leaf symplast of maize has been reported under saline conditions. High osmotic stress due to low external water potential, ion toxicity by sodium and/or chloride, and imbalanced nutrition due to interference with the uptake and transport of essential nutrients are three potential effects of salt stress on crop growth. The latter may not have an immediate effect because plants have some nutrient reserves which can be remobilized [10, 11]. Osmotic stress is linked to ion accumulation in the soil solution, whereas nutritional imbalance and specific ion effects are connected to ion buildup, mainly sodium and chloride, to toxic levels which interferes with the availability of other essential elements such as calcium and potassium [12]. Toxic levels of sodium in plant organs damage biological membranes and subcellular organelles, reducing growth and causing abnormal development before plant mortality [13, 14]. Several physiological processes such as photosynthesis, respiration, starch metabolism, and nitrogen fixation are also affected under saline conditions, leading to losses in crop productivity. Moreover, salt stress also induces oxidative damage to plant cells with overproduction of reactive oxygen species in maize [15]. The ability of plants to survive and produce harvestable yields under salt stress is called salt resistance. Salt resistance is a complex phenomenon, and plants manifest a variety of adaptations at subcellular, cellular, and organ levels such as stomatal regulation, ion homeostasis, hormonal balance, activation of the antioxidant defense system, osmotic adjustment, and maintenance of tissue water status to grow successfully under salinity [16–20]. An integrated approach encompassing conventional breeding together with marker-assisted selection, biotechnology, exogenous use of growth regulators/ osmoprotectants, and nutrient management may be needed for successful maize

growth and cause severe wilting [9].

cultivation on salt-affected soils [21–23].

**3.1 Salinity stress response on seed germination**

**42**

**3. The response of salinity stress on maize plant physiology**

the first phase of salt stress without reaching toxic sodium concentrations.

Salt stress affects the growth and development of maize; however, the response of plants varies with the degree of stress and crop growth stage. Short-term exposure of maize plants to salt stress influences plant growth, owing to osmotic stress in

Seed germination is the most critical stage in a seedling establishment which determines the success of crop production on salt-affected soils. Generally, salt

**2. Salinity stress**

*Plant Stress Physiology*

required to uphold cell membrane integrity for proper functioning [43]. The high values for sodium/potassium, sodium/calcium, and sodium/magnesium ratios in the total plant and apoplast and symplast of expanding tissues in maize confirm that impaired transport of potassium, calcium, and magnesium by sodium might upset plant metabolism, leading to reduced growth under saline conditions. Besides potassium and calcium, nitrogen uptake and translocation are severely inhibited under salt stress, leading to reduced nitrogen contents in different maize tissues [41, 44]. Higher buildup of sodium and chloride concentrations in different plant tissues is the principal reason for nutritional imbalances. Accumulation of high sodium and chloride ions, due to salinity, in the rhizosphere decreases plant uptake of nitrogen, potassium, calcium, magnesium, and iron and thus causes severe nutritional imbalances in maize.

tonoplast hydrogen/sodium antiporters driven by the proton gradient is an important adaptive strategy for plants under salt stress. Through this strategy, maize plants not only evade the cytosol from the toxic effects of excessive sodium and gain tissue resistance for sodium but also significantly lower the osmotic potential which contributes to osmoregulation. In root cells of maize, shifting sodium into vacuoles through the tonoplast appears to be a viable strategy to minimize sodium transport to developing shoots [16]. Absorption of excessive sodium from xylem by parenchyma cells in the xylem to limit sodium translocation to shoots is also reported in maize [52]. However, salt tolerance in maize is not linked to sodium content in shoots, but rather the ability of cells to shift excessive sodium in vacuoles to maintain low sodium concentrations in the cytoplasm seemed more important [53]. Salt tolerance in maize is also linked with higher potassium and lower sodium and chloride fluxes and cytoplasmic contents and their ability to rule out sodium and chloride from leaves to sustain a higher potassium/sodium ratio. Moreover, shifting sodium and chloride in the stems and/or leaf sheaths to lessen the buildup of toxic ions in more sensitive leaf blades is another adaptive strategy of maize

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

Salinity-induced osmotic effects alter general metabolic processes and enzymatic activities, leading to over-generation of reactive oxygen species which causes oxidative stress in maize. Overproduction of reactive oxygen species is highly toxic and damages proteins, lipids, carbohydrates, and deoxyribonucleic acid. Photosystems I and II in chloroplasts and complex I, ubiquinone, and complex III of the electron transport chain in mitochondria are key sites for reactive oxygen species synthesis [55]. Plants have multigenic responses against salt stress that involve both osmotic and ionic homeostasis, as well as cell detoxification, which is primarily met by antioxidant defense mechanisms [56, 57]. The better leaf growth, leaf water content, and membrane stability index observed in salt-tolerant maize were associated with higher antioxidant activity with greater accumulation of polyphenols under saline conditions [19]. Catalase, ascorbate peroxidase, and guaiacol peroxidase enzymes in combination with superoxide dismutase have the greatest hydrogen peroxide scavenger activity in both leaves and roots of salt-stressed maize

Plant growth and development is governed by the synthesis of hormones with small amounts sufficient to regulate plant growth. Auxins, gibberellins, cytokinins, ethylene, and abscisic acid are the most important phytohormones; among them, the first three are growth promoters, while the other two are growth retardants. Maize plants under salt stress make certain modifications to the synthesis of these growth substances. In a saline environment, root tips are the first to sense impaired water availability due to the osmotic effect, sending a signal to shoots to adjust whole plant metabolism [18]. Higher abscisic acid levels in salt-tolerant maize help to minimize water loss and may even regulate growth promotion. Leaf growth sensitivity decreases as abscisic acid levels increase under such conditions.

Maize plants facing salt stress undergo a variety of adaptive mechanisms at the

downregulation of many gene transcripts are important [58]. Expression of antioxidant defense genes is triggered in maize to protect the cells from salinity-induced oxidative damage. In photosynthesizing shoots of maize, catalase activity increased due to the induction of mRNA accumulation in response to higher reactive oxygen species levels under salt stress. Likewise, the buildup of superoxide dismutase transcripts increased without any notable change in total superoxide dismutase enzymatic activity or isozyme profiles [9]. The alteration/adaptation in cell wall chemical composition may also contribute to salt resistance in maize, as a low

molecular level to counteract the damaging effects of salinity stress. Of these, accumulation or inhibition of several proteins and the upregulation and

plants in a saline environment [54].

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

plants [15].

**45**

Carbon fixation in maize is very sensitive to salt stress [45]. Reduced stomatal conductance, impaired activities of carbon fixation enzymes, reduced photosynthetic pigments, and destruction of photosynthetic apparatus are among the key factors limiting carbon fixation capacity of maize plants under salt stress [31, 46]. Total photosynthesis decreases due to inhibited leaf development and expansion as well as early leaf abscission, and as salt stress is prolonged, ion toxicity, membrane disruption, and complete stomatal closure become the prime factors responsible for photosynthetic inhibition. Salt stress affects stomatal conductance immediately due to perturbed water relations and shortly afterward due to the local synthesis of abscisic acid. Gas exchange analysis confirmed that reductions in net photosynthetic rates are connected with the limited availability of intercellular carbon dioxide due to reduced rates of transpiration and stomatal conductance in salt-treated maize plants.

Salt stress in maize, during the reproductive phase, decreases grain weight and number, resulting in substantial reductions in grain yield [47, 48]. Salinity-induced reductions in photosynthesis and sink limitations are the major causes of poor kernel settings and reduced grain number [49]. Salinity-induced reductions in assimilate translocation, from source to developing grains, are also responsible for poor grain setting and filling and ultimately grain yield [50].

### **4. Mechanisms of salt tolerance in maize**

Maize plants undergo a variety of adaptations at subcellular, cellular, and organ levels to grow successfully under salinity. Salt tolerance is a complex phenomenon; maize plants manifest several adaptations such as stomatal regulation, changes in hormonal balance, activation of the antioxidant defense system, osmotic adjustment, maintenance of tissue water contents, and various mechanisms of toxic ion exclusion under salt stress.

Osmotic adjustment or osmoregulation is the key adaptation of plants at the cellular level to minimize the effects of salinity-induced drought stress, especially during the first phase of salt stress. Osmoregulation is primarily met with the accretion of organic and inorganic solutes under salinity and/or drought to lower water potential without lessening actual water contents [51]. Soluble sugars, sugar alcohols, proline, glycine betaine, organic acids, and trehalose are among the major osmolytes. Proline and glycine betaine are the major osmolytes responsible for osmoregulation in maize under salt stress. Physiologically, the exclusion of excessive salt is an adaptive trait of plants to acquire salt resistance. Accumulation of sodium in excessive amounts is highly toxic for maize growth due to its strong interference with potassium, leading to disturbed stomatal regulation. Therefore, the exclusion of excessive sodium or its compartmentation into vacuoles through

### *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

tonoplast hydrogen/sodium antiporters driven by the proton gradient is an important adaptive strategy for plants under salt stress. Through this strategy, maize plants not only evade the cytosol from the toxic effects of excessive sodium and gain tissue resistance for sodium but also significantly lower the osmotic potential which contributes to osmoregulation. In root cells of maize, shifting sodium into vacuoles through the tonoplast appears to be a viable strategy to minimize sodium transport to developing shoots [16]. Absorption of excessive sodium from xylem by parenchyma cells in the xylem to limit sodium translocation to shoots is also reported in maize [52]. However, salt tolerance in maize is not linked to sodium content in shoots, but rather the ability of cells to shift excessive sodium in vacuoles to maintain low sodium concentrations in the cytoplasm seemed more important [53].

Salt tolerance in maize is also linked with higher potassium and lower sodium and chloride fluxes and cytoplasmic contents and their ability to rule out sodium and chloride from leaves to sustain a higher potassium/sodium ratio. Moreover, shifting sodium and chloride in the stems and/or leaf sheaths to lessen the buildup of toxic ions in more sensitive leaf blades is another adaptive strategy of maize plants in a saline environment [54].

Salinity-induced osmotic effects alter general metabolic processes and enzymatic activities, leading to over-generation of reactive oxygen species which causes oxidative stress in maize. Overproduction of reactive oxygen species is highly toxic and damages proteins, lipids, carbohydrates, and deoxyribonucleic acid. Photosystems I and II in chloroplasts and complex I, ubiquinone, and complex III of the electron transport chain in mitochondria are key sites for reactive oxygen species synthesis [55]. Plants have multigenic responses against salt stress that involve both osmotic and ionic homeostasis, as well as cell detoxification, which is primarily met by antioxidant defense mechanisms [56, 57]. The better leaf growth, leaf water content, and membrane stability index observed in salt-tolerant maize were associated with higher antioxidant activity with greater accumulation of polyphenols under saline conditions [19]. Catalase, ascorbate peroxidase, and guaiacol peroxidase enzymes in combination with superoxide dismutase have the greatest hydrogen peroxide scavenger activity in both leaves and roots of salt-stressed maize plants [15].

Plant growth and development is governed by the synthesis of hormones with small amounts sufficient to regulate plant growth. Auxins, gibberellins, cytokinins, ethylene, and abscisic acid are the most important phytohormones; among them, the first three are growth promoters, while the other two are growth retardants. Maize plants under salt stress make certain modifications to the synthesis of these growth substances. In a saline environment, root tips are the first to sense impaired water availability due to the osmotic effect, sending a signal to shoots to adjust whole plant metabolism [18]. Higher abscisic acid levels in salt-tolerant maize help to minimize water loss and may even regulate growth promotion. Leaf growth sensitivity decreases as abscisic acid levels increase under such conditions.

Maize plants facing salt stress undergo a variety of adaptive mechanisms at the molecular level to counteract the damaging effects of salinity stress. Of these, accumulation or inhibition of several proteins and the upregulation and downregulation of many gene transcripts are important [58]. Expression of antioxidant defense genes is triggered in maize to protect the cells from salinity-induced oxidative damage. In photosynthesizing shoots of maize, catalase activity increased due to the induction of mRNA accumulation in response to higher reactive oxygen species levels under salt stress. Likewise, the buildup of superoxide dismutase transcripts increased without any notable change in total superoxide dismutase enzymatic activity or isozyme profiles [9]. The alteration/adaptation in cell wall chemical composition may also contribute to salt resistance in maize, as a low

required to uphold cell membrane integrity for proper functioning [43]. The high values for sodium/potassium, sodium/calcium, and sodium/magnesium ratios in the total plant and apoplast and symplast of expanding tissues in maize confirm that impaired transport of potassium, calcium, and magnesium by sodium might upset plant metabolism, leading to reduced growth under saline conditions. Besides potassium and calcium, nitrogen uptake and translocation are severely inhibited under salt stress, leading to reduced nitrogen contents in different maize tissues [41, 44]. Higher buildup of sodium and chloride concentrations in different plant tissues is the principal reason for nutritional imbalances. Accumulation of high sodium and chloride ions, due to salinity, in the rhizosphere decreases plant uptake of nitrogen, potassium, calcium, magnesium, and iron and thus causes severe

Carbon fixation in maize is very sensitive to salt stress [45]. Reduced stomatal conductance, impaired activities of carbon fixation enzymes, reduced photosynthetic pigments, and destruction of photosynthetic apparatus are among the key factors limiting carbon fixation capacity of maize plants under salt stress [31, 46]. Total photosynthesis decreases due to inhibited leaf development and expansion as well as early leaf abscission, and as salt stress is prolonged, ion toxicity, membrane disruption, and complete stomatal closure become the prime factors responsible for photosynthetic inhibition. Salt stress affects stomatal conductance immediately due to perturbed water relations and shortly afterward due to the local synthesis of abscisic acid. Gas exchange analysis confirmed that reductions in net photosynthetic rates are connected with the limited availability of intercellular carbon dioxide due to reduced rates of transpiration and stomatal conductance in salt-treated

Salt stress in maize, during the reproductive phase, decreases grain weight and number, resulting in substantial reductions in grain yield [47, 48]. Salinity-induced reductions in photosynthesis and sink limitations are the major causes of poor kernel settings and reduced grain number [49]. Salinity-induced reductions in assimilate translocation, from source to developing grains, are also responsible for

Maize plants undergo a variety of adaptations at subcellular, cellular, and organ levels to grow successfully under salinity. Salt tolerance is a complex phenomenon; maize plants manifest several adaptations such as stomatal regulation, changes in hormonal balance, activation of the antioxidant defense system, osmotic adjustment, maintenance of tissue water contents, and various mechanisms of toxic ion

Osmotic adjustment or osmoregulation is the key adaptation of plants at the cellular level to minimize the effects of salinity-induced drought stress, especially during the first phase of salt stress. Osmoregulation is primarily met with the accretion of organic and inorganic solutes under salinity and/or drought to lower water potential without lessening actual water contents [51]. Soluble sugars, sugar alcohols, proline, glycine betaine, organic acids, and trehalose are among the major osmolytes. Proline and glycine betaine are the major osmolytes responsible for osmoregulation in maize under salt stress. Physiologically, the exclusion of excessive salt is an adaptive trait of plants to acquire salt resistance. Accumulation of sodium in excessive amounts is highly toxic for maize growth due to its strong interference with potassium, leading to disturbed stomatal regulation. Therefore, the exclusion of excessive sodium or its compartmentation into vacuoles through

poor grain setting and filling and ultimately grain yield [50].

**4. Mechanisms of salt tolerance in maize**

exclusion under salt stress.

**44**

nutritional imbalances in maize.

*Plant Stress Physiology*

maize plants.

accumulation of non-methylated uronic acid in leaf cell walls may contribute to salt resistance in the first phase of salt stress [59].

physiological parameters of the crop. Thidiazuron proved more efficient in alleviating the adverse effects of salinity than potassium and boron. Potassium content, chlorophyll content, total carbohydrate protein percentage, and total soluble salt percentage were substantially improved by foliar application of thidiazuron; how-

Flue gas desulfurization gypsum (FGDG) application can reduce sodium toxicity by replacing it with calcium at the cation exchange site and results in increased clay particle flocculation near the surface of the soil [70]. Furfural residue is rich in organic carbon and can increase the SOC content, reduce soil bulk density, and lower soil pH [71]. Flue gas desulfurization gypsum and furfural residue combined application reduced the yield gap of maize and recovered soil properties. Flue gas desulfurization gypsum and furfural residue increased the organic carbon (SOC) and calcium contents and decreased the upper soil layer pH and sodium content. Mineral nutrients like phosphorus, nitrogen, potassium, magnesium, and calcium accumulations in maize increased significantly, and sodium accumulation decreased in the flue gas desulfurization gypsum and furfural residue treatment compared

Hydrogen peroxide as foliar spray effectively curtailed the effects induced by salinity because of increased antioxidant enzyme activities: ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, and the most responsive catalase [73]. Salicylic acid is an imperative secondary metabolite that is used in salinity management as it induces resistance against salinity in plants by regulating physiological processes through signaling. Maize plants exposed to sodium chloride induced salinity, reduced plant dry biomass, increased membrane permeability, and reduced nutrient availability, while those plants supplied with exogenous salicylic acid increased dry biomass, decreased membrane permeability and lipid peroxidation, and increased iron, zinc, copper, and manganese contents. Salicylic acid application further improved nutrient uptake by maize plants except for zinc in the saline condition.

Salicylic acid reduced chloride and sodium accumulation considerably [22].

In another study, a maize crop dry weight and leaf area decreased by 51.43 and 53.18%, respectively, when irrigated with saline water, while salicylic acid foliar application at the rate of 200 ppm remedied the harmful salinity effects and improved whole plant dry weights and leaf area and improved proline and amino acid contents such as lysine, arginine, glutamic acid, and serine accumulation under

Organic amendments proved as an effective strategy for saline soil amelioration. Organic amendments improve soil chemical and physical properties. Solid waste, vermicompost, and cow dung influence soil salinity and alleviate its adverse effects on the growth of plants by changing the physico-chemical properties of soil. Solid waste, vermicompost, and cow dung reduced soil electrical conductivity as well as

Compost and vermicompost application increased maize plant dry matter and plant height and reduced soil pH and electrical conductivity. Extractable phosphorus, total nitrogen, soil organic carbon, cation exchange capacity, and potassium, calcium, and magnesium concentrations were improved by the application of vermicompost and compost. Sodium concentration decreased because of its replacement by calcium ions and then leaching. This results in a decrease in soil

Biochar also improved physico-chemical properties of soil, including soil cation exchange capacity, pH, water holding capacity, surface area, and soil structure under abiotic stresses [77]. Biochar application improved potassium availability uptake and decreased sodium availability and uptake under salt stress [78, 79]. Biochar made by cow manure is a rich source of many plant nutrients which

ever, transpiration rate and proline content were decreased [69].

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

with control [72].

saline stress conditions [74].

salinity levels [76].

**47**

improved shoot and root length [75].

### **5. Management strategies**

Remediation of salt affected areas with low cost, efficient, and adaptable methods is a challenging goal for scientists [11]. Different practices are used to improve growth and tolerance of crops in salt-affected areas.

### **5.1 Agronomic approaches (soil amendments)**

For saline soil management, many chemicals and organic amendments are applied to combat the adverse effect of salinity in maize crops. Chemicals mostly applied to soil for maize crops include silicon, salicylic acid, potassium, phosphorus, gypsum, biochar, and boron, and many organic amendments are also applied. Silicon application and an increase in their availability reduce the changes caused by salinity in plants by altering the plant and soil factors [60]. Silicon application increases the photosynthetic apparatus efficiency of maize plants under salinity stress by improving and maintaining the continuity of the electron transport chain [61] Silicon is recognized as a resistance improver against salinity in the maize crop. Silicon application lessened both oxidative and osmotic stress in maize crops by improving the defensive machinery performance under salinity stress. Silicon also improved water-use efficiency. Silicon-treated maize plants showed better survival under saline conditions, and their biochemical and photosynthetic apparatus was better working than silicon non-treated plants [62]. The application of brackish water is also reported in maize plants to reclaim salt effects. Brackish water irrigation boosted K uptake and retarded Na uptake in some maize genotypes. Selection of tolerant genotypes for growing in salt affected areas would be a better reclamation method [63]. Boron is an important element for many biochemical and physiological reactions of plants [64]. Boron application alleviated the negative effect of sodium chloride-induced salinity in sweet corn. Boron improved potassium concentration and maintained membrane integrity [65]. Combined application of silicon and boron also proved effective in alleviating the salinity effect on maize crops. They both in combination enhanced maize plant physical and biological parameters and also increased total soluble sugars and proline content [66]. In saline conditions, sodium concentration increased that caused an imbalance in sodium to potassium ratio. Application of potassium maintained or lowered this ratio and alleviates the deleterious effects of sodium. Potassium application to maize crop grown in saline soil decreased sodium percentage and enhanced potassium percentage in maize grain and stalk as well as distinctly boosted the maize salt tolerance by decreasing the sodium to potassium ratio. The most significant effect was observed at higher potassium fertilizer application rates [67].

Combined application of potassium sulfate and diammonium phosphate on maize in saline soil for maize (*Zea mays* L.) showed that maize responded well to potassium and phosphorus fertilization. Salinity effects were amended by potassium and phosphorus fertilizer application and improved yield. The influence of potassium was great on grain yield compared to phosphorus. K affected yieldrelated parameters, and phosphorus showed substantial effects on sodium, potassium, magnesium, and sodium to potassium ratio. Potassium application decreased sodium concentration and ultimately decreased sodium to potassium ratio [68]. Foliar application of potassium chloride, boron, and thidiazuron was done on maize crops in saline stress. Thidiazuron and potassium application improved the

### *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

physiological parameters of the crop. Thidiazuron proved more efficient in alleviating the adverse effects of salinity than potassium and boron. Potassium content, chlorophyll content, total carbohydrate protein percentage, and total soluble salt percentage were substantially improved by foliar application of thidiazuron; however, transpiration rate and proline content were decreased [69].

Flue gas desulfurization gypsum (FGDG) application can reduce sodium toxicity by replacing it with calcium at the cation exchange site and results in increased clay particle flocculation near the surface of the soil [70]. Furfural residue is rich in organic carbon and can increase the SOC content, reduce soil bulk density, and lower soil pH [71]. Flue gas desulfurization gypsum and furfural residue combined application reduced the yield gap of maize and recovered soil properties. Flue gas desulfurization gypsum and furfural residue increased the organic carbon (SOC) and calcium contents and decreased the upper soil layer pH and sodium content. Mineral nutrients like phosphorus, nitrogen, potassium, magnesium, and calcium accumulations in maize increased significantly, and sodium accumulation decreased in the flue gas desulfurization gypsum and furfural residue treatment compared with control [72].

Hydrogen peroxide as foliar spray effectively curtailed the effects induced by salinity because of increased antioxidant enzyme activities: ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, and the most responsive catalase [73].

Salicylic acid is an imperative secondary metabolite that is used in salinity management as it induces resistance against salinity in plants by regulating physiological processes through signaling. Maize plants exposed to sodium chloride induced salinity, reduced plant dry biomass, increased membrane permeability, and reduced nutrient availability, while those plants supplied with exogenous salicylic acid increased dry biomass, decreased membrane permeability and lipid peroxidation, and increased iron, zinc, copper, and manganese contents. Salicylic acid application further improved nutrient uptake by maize plants except for zinc in the saline condition. Salicylic acid reduced chloride and sodium accumulation considerably [22].

In another study, a maize crop dry weight and leaf area decreased by 51.43 and 53.18%, respectively, when irrigated with saline water, while salicylic acid foliar application at the rate of 200 ppm remedied the harmful salinity effects and improved whole plant dry weights and leaf area and improved proline and amino acid contents such as lysine, arginine, glutamic acid, and serine accumulation under saline stress conditions [74].

Organic amendments proved as an effective strategy for saline soil amelioration. Organic amendments improve soil chemical and physical properties. Solid waste, vermicompost, and cow dung influence soil salinity and alleviate its adverse effects on the growth of plants by changing the physico-chemical properties of soil. Solid waste, vermicompost, and cow dung reduced soil electrical conductivity as well as improved shoot and root length [75].

Compost and vermicompost application increased maize plant dry matter and plant height and reduced soil pH and electrical conductivity. Extractable phosphorus, total nitrogen, soil organic carbon, cation exchange capacity, and potassium, calcium, and magnesium concentrations were improved by the application of vermicompost and compost. Sodium concentration decreased because of its replacement by calcium ions and then leaching. This results in a decrease in soil salinity levels [76].

Biochar also improved physico-chemical properties of soil, including soil cation exchange capacity, pH, water holding capacity, surface area, and soil structure under abiotic stresses [77]. Biochar application improved potassium availability uptake and decreased sodium availability and uptake under salt stress [78, 79]. Biochar made by cow manure is a rich source of many plant nutrients which

accumulation of non-methylated uronic acid in leaf cell walls may contribute to salt

Remediation of salt affected areas with low cost, efficient, and adaptable methods is a challenging goal for scientists [11]. Different practices are used to

For saline soil management, many chemicals and organic amendments are applied to combat the adverse effect of salinity in maize crops. Chemicals mostly applied to soil for maize crops include silicon, salicylic acid, potassium, phosphorus, gypsum, biochar, and boron, and many organic amendments are also applied. Silicon application and an increase in their availability reduce the changes caused by salinity in plants by altering the plant and soil factors [60]. Silicon application increases the photosynthetic apparatus efficiency of maize plants under salinity stress by improving and maintaining the continuity of the electron transport chain [61] Silicon is recognized as a resistance improver against salinity in the maize crop. Silicon application lessened both oxidative and osmotic stress in maize crops by improving the defensive machinery performance under salinity stress. Silicon also improved water-use efficiency. Silicon-treated maize plants showed better survival under saline conditions, and their biochemical and photosynthetic apparatus was better working than silicon non-treated plants [62]. The application of brackish water is also reported in maize plants to reclaim salt effects. Brackish water irrigation boosted K uptake and retarded Na uptake in some maize genotypes. Selection of tolerant genotypes for growing in salt affected areas would be a better reclamation method [63]. Boron is an important element for many biochemical and physiological reactions of plants [64]. Boron application alleviated the negative effect of sodium chloride-induced salinity in sweet corn. Boron improved potassium concentration and maintained membrane integrity [65]. Combined application of silicon and boron also proved effective in alleviating the salinity effect on maize crops. They both in combination enhanced maize plant physical and biological parameters and also increased total soluble sugars and proline content [66]. In saline conditions, sodium concentration increased that caused an imbalance in sodium to potassium ratio. Application of potassium maintained or lowered this ratio and alleviates the deleterious effects of sodium. Potassium application to maize crop grown in saline soil decreased sodium percentage and enhanced potassium percentage in maize grain and stalk as well as distinctly boosted the maize salt tolerance by decreasing the sodium to potassium ratio. The most significant effect was observed at higher

Combined application of potassium sulfate and diammonium phosphate on maize in saline soil for maize (*Zea mays* L.) showed that maize responded well to potassium and phosphorus fertilization. Salinity effects were amended by potassium and phosphorus fertilizer application and improved yield. The influence of potassium was great on grain yield compared to phosphorus. K affected yieldrelated parameters, and phosphorus showed substantial effects on sodium, potassium, magnesium, and sodium to potassium ratio. Potassium application decreased sodium concentration and ultimately decreased sodium to potassium ratio [68]. Foliar application of potassium chloride, boron, and thidiazuron was done on maize

crops in saline stress. Thidiazuron and potassium application improved the

improve growth and tolerance of crops in salt-affected areas.

resistance in the first phase of salt stress [59].

**5.1 Agronomic approaches (soil amendments)**

potassium fertilizer application rates [67].

**46**

**5. Management strategies**

*Plant Stress Physiology*

significantly increased nutrient uptake in maize crop. Cow manure biochar application improved net WUE, field-saturated hydraulic conductivity, and significantly increased Oslen-P, total N, pH, total C, exchangeable cations, and cation exchange capacity [80]. Compost manure and crop straw biochar and pyroligneous solution can improve maize productivity and combat salinity stress. Compost manure and crop straw biochar both increased nutrient statuses and decreased salinity by reducing chloride and sodium accumulation and increasing potassium concentration. Manures also increased plant performance, maize grain yield, and leaf area index, with a decrease in electrolyte leakage. Leaf bioactivity associated with osmotic stress was improved significantly [81]. It is concluded that exogenously applied organic matters such as plant residues, manure, a by-product of municipal or farming activities, etc. are an efficient and feasible way to mitigate the effects of salinity on plant growth and soil health. Organic amendments at optimal rates (>50 tons per hectare) can improve soil chemical like cation exchangeable capacity, pH, etc. and physical properties like permeability, soil structure, water holding capacity, etc., approving maize plant growth [82].

uptake along with a noteworthy decrease in sodium uptake that resulted in better

concentration which sustained membrane permeability [89]. A comparison

for copper and manganese [90].

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

**5.3 Application of PGPR**

*5.3.1 Osmotic adjustment*

**49**

between gibberellic acid and salicylic acid under the saline condition in maize plant showed that gibberellic acid was more efficient in resisting salinity effect on leaves than salicylic acid. Gibberellic acid also improved the nutrient status of plant except

Soil has an enormous microbial versatility that belongs to different groups of fungi, Archaea, and bacteria [91]. Microorganisms are used in agricultural fields, and they can lessen many abiotic stresses [92, 93]. Usually, bacteria are used for promoting plant growth and alleviating many abiotic stresses. These bacteria are usually termed as plant growth-promoting rhizobacteria (PGPR). PGPR is

rhizospheric or endophytic bacteria that colonize the root either interiorly or exteriorly. Bacterial genera such as *Achromobacter*, *Azospirillum*, *Bacillus*, *Burkholderia*, *Enterobacter*, *Methylobacterium*, *Microbacterium*, *Paenibacillus*, *Pantoea*, *Pseudomonas*, *Rhizobium*, *Variovorax*, etc. provide tolerance to host plants against abiotic stresses [94, 95]. Stress tolerance is boosted by microbes by various mechanisms and production of indoleacetic acid, gibberellins, and many other elements. These elements improved the root growth and enhance nutrient content, thus improving the plant health under salt stress [95]. Bacteria that help plants in alleviating salt stress are called halotolerant or salt-tolerant or salt-loving bacteria. These

halotolerant microbes have vital importance in the field of agriculture. In arid and semi-arid regions, they improve crop productivity [91]. Specific PGPR inoculations help to boost salt stress tolerance in plants by induced systemic tolerance (IST). Induced systemic tolerance changes many biochemical and functional characteristics. The PGPR improves salinity tolerance by either direct mechanism (indoleacetic acid (IAA) synthesis phosphate solubilization, nitrogen fixation, etc.) or indirect mechanism (exopolysaccharides (EPS), antioxidant defense, osmotic balance, and volatile organic compounds (VOCs)) and improves plant growth [96] (**Table 1**).

Osmotic adjustment is the maintenance of cell turgidity by increasing compatible solutes, vital for regular cell functioning. Compatible solutes decrease osmotic stress caused by salts [55]. PGPR produce and secrete compatible osmolytes to mitigate the harmful effect of salts and help plants improve their growth. Proline is the main osmolytes in reducing osmotic stress and produced by the hydrolysis of proteins in the plant. Under salt stress, glycine betaine and proline are usually produced and accumulated in plants. There is a dearth of organic osmolytes pro-

duction such as trehalose in plants [112]. Under salinity, proline plays a

multifunctional role like regulating cytosolic acidity, protein maintenance, ROS

The combined application of sodium chloride-induced salinity and gibberellic acid on maize plant growth and nutritional status was studied. Salinity decreased chlorophyll content, total dry matter, and relative water content, whereas increased enzyme activities peroxidase polyphenol oxidase superoxide dismutase and proline accumulation. Gibberellic acid overcame the deleterious effects of sodium chlorideinduced salinity stress on the above physiological characteristics to a variable extent. Gibberellic acid decreased enzyme activities and increased physiological parameters and macro- and micronutrient concentration. Foliar application of gibberellic acid counteracted some salinity adverse effects by the buildup of proline

growth and yield of maize plant under salt stress condition [88].

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

### **5.2 Application of hormones**

Hormones govern many processes inside plants that regulate plant growth: auxins, gibberellins, and cytokinins are growth promoter hormones, while abscisic acid and ethylene are the growth retardants. Under salt stress conditions, growthpromoting hormones are applied exogenously to overcome the adverse effects of salinity on maize plant growth and development.

Cytokinin is a plant growth regulator that plays a vital role in cytokinindependent processes that regulate plant adaptation, growth, and development processes [83]. It is reported in recent research that cytokinins of developing maize seeds may come from both transport and local synthesis. Cytokinin fertilization at higher rates suggested parental control on plant metabolism [84]. Cytokinin and auxin application alone or in combination with maize plants reduced the deleterious effect of salinity on plant growth and increased physical parameters like stem diameter, plant height, ear length, row number per ear, and biological yield like grain yield and number at different concentrations. A single application of cytokinin played a role in improving kernel number per row, while a single application of auxin increased grain weight and better harvest index in saline condition [85].

Kinetin is one form of cytokinins and is known to boost the crop plant growth grown under saline conditions [86]. Kinetin and indoleacetic acid (auxin) applications as foliar spray overcame to adversative effects of sodium chloride induced stress on physiological parameters at the earlier stages of maize plants at a variable extent. Foliar combined application of both kinetin and indoleacetic acid substantially increased K<sup>+</sup> and Ca2+ concentration and reduced those of Na<sup>+</sup> . Their application also increased essential inorganic nutrients and maintained membrane permeability and in result thwarted some salt-persuaded adversative effects [19]. Exogenous combined application of inorganic nutrients and indoleacetic acid improved phosphorus, calcium, and magnesium contents and decreased sodium concentration in maize plants grown in saline condition. Improvement in growth by indoleacetic acid and organic nutrient application is linked with an improved concentration of photosynthetic pigment, more leaf sodium to potassium ratio, rehabilitated activities of some antioxidant enzymes such as CAT and SOD, and reduced membrane permeability under salinity. Exogenous foliar application of indoleacetic acid additionally improved the CAT and SOD activities in salt-stressed maize plants, while increasing effect was not detected in activities of POX or PPO [87]. Previously, foliar application of indoleacetic acid enhanced the essential nutrient

### *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

uptake along with a noteworthy decrease in sodium uptake that resulted in better growth and yield of maize plant under salt stress condition [88].

The combined application of sodium chloride-induced salinity and gibberellic acid on maize plant growth and nutritional status was studied. Salinity decreased chlorophyll content, total dry matter, and relative water content, whereas increased enzyme activities peroxidase polyphenol oxidase superoxide dismutase and proline accumulation. Gibberellic acid overcame the deleterious effects of sodium chlorideinduced salinity stress on the above physiological characteristics to a variable extent. Gibberellic acid decreased enzyme activities and increased physiological parameters and macro- and micronutrient concentration. Foliar application of gibberellic acid counteracted some salinity adverse effects by the buildup of proline concentration which sustained membrane permeability [89]. A comparison between gibberellic acid and salicylic acid under the saline condition in maize plant showed that gibberellic acid was more efficient in resisting salinity effect on leaves than salicylic acid. Gibberellic acid also improved the nutrient status of plant except for copper and manganese [90].

### **5.3 Application of PGPR**

significantly increased nutrient uptake in maize crop. Cow manure biochar application improved net WUE, field-saturated hydraulic conductivity, and significantly increased Oslen-P, total N, pH, total C, exchangeable cations, and cation exchange capacity [80]. Compost manure and crop straw biochar and pyroligneous solution can improve maize productivity and combat salinity stress. Compost manure and crop straw biochar both increased nutrient statuses and decreased salinity by reducing chloride and sodium accumulation and increasing potassium concentration. Manures also increased plant performance, maize grain yield, and leaf area index, with a decrease in electrolyte leakage. Leaf bioactivity associated with osmotic stress was improved significantly [81]. It is concluded that exogenously applied organic matters such as plant residues, manure, a by-product of municipal or farming activities, etc. are an efficient and feasible way to mitigate the effects of salinity on plant growth and soil health. Organic amendments at optimal rates (>50 tons per hectare) can improve soil chemical like cation exchangeable capacity, pH, etc. and physical properties like permeability, soil structure, water holding capacity,

Hormones govern many processes inside plants that regulate plant growth: auxins, gibberellins, and cytokinins are growth promoter hormones, while abscisic acid and ethylene are the growth retardants. Under salt stress conditions, growthpromoting hormones are applied exogenously to overcome the adverse effects of

Cytokinin is a plant growth regulator that plays a vital role in cytokinindependent processes that regulate plant adaptation, growth, and development processes [83]. It is reported in recent research that cytokinins of developing maize seeds may come from both transport and local synthesis. Cytokinin fertilization at higher rates suggested parental control on plant metabolism [84]. Cytokinin and auxin application alone or in combination with maize plants reduced the deleterious effect of salinity on plant growth and increased physical parameters like stem diameter, plant height, ear length, row number per ear, and biological yield like grain yield and number at different concentrations. A single application of cytokinin played a role in improving kernel number per row, while a single application of auxin increased grain weight and better harvest index in saline condition [85]. Kinetin is one form of cytokinins and is known to boost the crop plant growth grown under saline conditions [86]. Kinetin and indoleacetic acid (auxin) applications as foliar spray overcame to adversative effects of sodium chloride induced stress on physiological parameters at the earlier stages of maize plants at a variable extent. Foliar combined application of both kinetin and indoleacetic acid substan-

tially increased K<sup>+</sup> and Ca2+ concentration and reduced those of Na<sup>+</sup>

tion also increased essential inorganic nutrients and maintained membrane permeability and in result thwarted some salt-persuaded adversative effects [19]. Exogenous combined application of inorganic nutrients and indoleacetic acid improved phosphorus, calcium, and magnesium contents and decreased sodium concentration in maize plants grown in saline condition. Improvement in growth by indoleacetic acid and organic nutrient application is linked with an improved concentration of photosynthetic pigment, more leaf sodium to potassium ratio, rehabilitated activities of some antioxidant enzymes such as CAT and SOD, and reduced membrane permeability under salinity. Exogenous foliar application of indoleacetic acid additionally improved the CAT and SOD activities in salt-stressed maize plants, while increasing effect was not detected in activities of POX or PPO [87]. Previously, foliar application of indoleacetic acid enhanced the essential nutrient

. Their applica-

etc., approving maize plant growth [82].

salinity on maize plant growth and development.

**5.2 Application of hormones**

*Plant Stress Physiology*

**48**

Soil has an enormous microbial versatility that belongs to different groups of fungi, Archaea, and bacteria [91]. Microorganisms are used in agricultural fields, and they can lessen many abiotic stresses [92, 93]. Usually, bacteria are used for promoting plant growth and alleviating many abiotic stresses. These bacteria are usually termed as plant growth-promoting rhizobacteria (PGPR). PGPR is rhizospheric or endophytic bacteria that colonize the root either interiorly or exteriorly. Bacterial genera such as *Achromobacter*, *Azospirillum*, *Bacillus*, *Burkholderia*, *Enterobacter*, *Methylobacterium*, *Microbacterium*, *Paenibacillus*, *Pantoea*, *Pseudomonas*, *Rhizobium*, *Variovorax*, etc. provide tolerance to host plants against abiotic stresses [94, 95]. Stress tolerance is boosted by microbes by various mechanisms and production of indoleacetic acid, gibberellins, and many other elements. These elements improved the root growth and enhance nutrient content, thus improving the plant health under salt stress [95]. Bacteria that help plants in alleviating salt stress are called halotolerant or salt-tolerant or salt-loving bacteria. These halotolerant microbes have vital importance in the field of agriculture. In arid and semi-arid regions, they improve crop productivity [91]. Specific PGPR inoculations help to boost salt stress tolerance in plants by induced systemic tolerance (IST). Induced systemic tolerance changes many biochemical and functional characteristics. The PGPR improves salinity tolerance by either direct mechanism (indoleacetic acid (IAA) synthesis phosphate solubilization, nitrogen fixation, etc.) or indirect mechanism (exopolysaccharides (EPS), antioxidant defense, osmotic balance, and volatile organic compounds (VOCs)) and improves plant growth [96] (**Table 1**).

### *5.3.1 Osmotic adjustment*

Osmotic adjustment is the maintenance of cell turgidity by increasing compatible solutes, vital for regular cell functioning. Compatible solutes decrease osmotic stress caused by salts [55]. PGPR produce and secrete compatible osmolytes to mitigate the harmful effect of salts and help plants improve their growth. Proline is the main osmolytes in reducing osmotic stress and produced by the hydrolysis of proteins in the plant. Under salt stress, glycine betaine and proline are usually produced and accumulated in plants. There is a dearth of organic osmolytes production such as trehalose in plants [112]. Under salinity, proline plays a multifunctional role like regulating cytosolic acidity, protein maintenance, ROS


maize plant by production of proline that helps in osmotic adjustments [103]. *Azotobacter chroococcum* improved nutrition [108], *Geobacillus* sp. increased photosynthetic rate [111], and *Rhizobium* spp., *Rhizobium tropici* strain CIAT, *A. brasilense* strains Ab-V5 and Ab-V6 [107], and *A. faecalis* [101] enhanced chlorophyll content and photosynthetic rate by increased accumulation of proline and osmotic adjust-

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

Plants normally produce reactive oxygen species during cellular metabolism in less quantity. However, under salinity stress conditions, increased production of reactive oxygen species occurs, which alters redox state, denatures membrane bound proteins, reduces fluidity of membrane, causes DNA damage, destroys enzymatic actions, changes formation of protein, and destroys cell homeostasis, which can damage the cell and finally cause cell death [113]. PGPR excrete many enzymatic antioxidants (ascorbate peroxidase (APX), catalase (CAT) dehydroascorbate reductase, glutathione reductase (GR), superoxide dismutase (SOD), non-enzymatic antioxidants, ascorbate, tocopherols, glutathione, and cysteine) [114]. *Staphylococcus sciuri* induction induces more antioxidant production in maize plants that helped in the degradation of reactive oxygen species and improved plant growth [94]. *A. faecalis* [101], *Serratia liquefaciens* KM4 [106], and *Bacillus* sp. [104] are reported to increased maize growth, nutrition, and photosynthetic rate by producing more antioxidative enzymes. *Azotobacter vinelandii*, *Pseudomonas fluorescens*, and *Pseudomonas putida* restored lipids and antioxidant enzymes perox-

idase and catalase to semi-normal levels under saline condition [115].

PGPR produce exopolysaccharides (EPS), which are either homo- or heteropolysaccharides. These EPS bind to the cell surface like a capsule and make a biofilm [116]. Different microbes produce different types of polysaccharides, but some common monomers comprise glucose, galactose, and mannose. Uronic acids (fucose and rhamnose), amino sugars (N-acetylamino sugars), neutral sugars (galacturonic), pyruvate ketals, and ester-linked substituents are EPS constituents [117]. PGPR produce EPS and form hydrophilic biofilms under saline conditions and improve plant growth significantly [118]. EPS producing PGPR makes rhizosheaths around roots that help fight against salt stress by attaching Na+ ions with EPS. Attachment of Na+ ions to EPS decreases the toxicity of Na+ and makes it inaccessible for plants [119]. *P. aeruginosa* improved plant growth because of more EPS content production. *Pseudomonas* spp. produced more EPS and increased root growth and nutrition in maize plants [101]. Many other PGPRs such as *Gracilibacillus*, *Salinicoccus*, *Staphylococcus*, *Zhihengliuella*, *Bacillus*, *Brevibacterium*, *Virgibacillus*, *Oceanobacillus*, *Arthrobacter*, *Exiguobacterium*, and *Halomonas* spp. are reported to improve maize growth by the formation of biofilm [102]. *B. amyloliquefaciens* improved plant growth by the accu-

Rhizobacteria that produce lipophilic fluids with high vapor pressures are called volatile organic compounds. They communicate by cell signaling between organisms to improve growth. The VOCs are species-specific and promote the biosynthesis of glycine betaine and choline. These osmolytes improve plant tolerance

ments in maize plants.

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

*5.3.3 Exopolysaccharides*

mulation of soluble sugar content [109].

*5.3.4 Volatile organic carbons*

**51**

*5.3.2 Antioxidants*

### **Table 1.**

*PGPR and their mechanisms for salt tolerance.*

scavenging decrease in peroxidation of lipids, etc. PGPR inoculation in plants showed improved proline levels under salt stress. *Arthrobacter pascens* inoculation produces more proline in corn plants [104]. *Pseudomonas* spp. improved growth of

### *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

maize plant by production of proline that helps in osmotic adjustments [103]. *Azotobacter chroococcum* improved nutrition [108], *Geobacillus* sp. increased photosynthetic rate [111], and *Rhizobium* spp., *Rhizobium tropici* strain CIAT, *A. brasilense* strains Ab-V5 and Ab-V6 [107], and *A. faecalis* [101] enhanced chlorophyll content and photosynthetic rate by increased accumulation of proline and osmotic adjustments in maize plants.

### *5.3.2 Antioxidants*

Plants normally produce reactive oxygen species during cellular metabolism in less quantity. However, under salinity stress conditions, increased production of reactive oxygen species occurs, which alters redox state, denatures membrane bound proteins, reduces fluidity of membrane, causes DNA damage, destroys enzymatic actions, changes formation of protein, and destroys cell homeostasis, which can damage the cell and finally cause cell death [113]. PGPR excrete many enzymatic antioxidants (ascorbate peroxidase (APX), catalase (CAT) dehydroascorbate reductase, glutathione reductase (GR), superoxide dismutase (SOD), non-enzymatic antioxidants, ascorbate, tocopherols, glutathione, and cysteine) [114]. *Staphylococcus sciuri* induction induces more antioxidant production in maize plants that helped in the degradation of reactive oxygen species and improved plant growth [94]. *A. faecalis* [101], *Serratia liquefaciens* KM4 [106], and *Bacillus* sp. [104] are reported to increased maize growth, nutrition, and photosynthetic rate by producing more antioxidative enzymes. *Azotobacter vinelandii*, *Pseudomonas fluorescens*, and *Pseudomonas putida* restored lipids and antioxidant enzymes peroxidase and catalase to semi-normal levels under saline condition [115].

### *5.3.3 Exopolysaccharides*

PGPR produce exopolysaccharides (EPS), which are either homo- or heteropolysaccharides. These EPS bind to the cell surface like a capsule and make a biofilm [116]. Different microbes produce different types of polysaccharides, but some common monomers comprise glucose, galactose, and mannose. Uronic acids (fucose and rhamnose), amino sugars (N-acetylamino sugars), neutral sugars (galacturonic), pyruvate ketals, and ester-linked substituents are EPS constituents [117]. PGPR produce EPS and form hydrophilic biofilms under saline conditions and improve plant growth significantly [118]. EPS producing PGPR makes rhizosheaths around roots that help fight against salt stress by attaching Na+ ions with EPS. Attachment of Na+ ions to EPS decreases the toxicity of Na+ and makes it inaccessible for plants [119]. *P. aeruginosa* improved plant growth because of more EPS content production. *Pseudomonas* spp. produced more EPS and increased root growth and nutrition in maize plants [101]. Many other PGPRs such as *Gracilibacillus*, *Salinicoccus*, *Staphylococcus*, *Zhihengliuella*, *Bacillus*, *Brevibacterium*, *Virgibacillus*, *Oceanobacillus*, *Arthrobacter*, *Exiguobacterium*, and *Halomonas* spp. are reported to improve maize growth by the formation of biofilm [102]. *B. amyloliquefaciens* improved plant growth by the accumulation of soluble sugar content [109].

### *5.3.4 Volatile organic carbons*

Rhizobacteria that produce lipophilic fluids with high vapor pressures are called volatile organic compounds. They communicate by cell signaling between organisms to improve growth. The VOCs are species-specific and promote the biosynthesis of glycine betaine and choline. These osmolytes improve plant tolerance

scavenging decrease in peroxidation of lipids, etc. PGPR inoculation in plants showed improved proline levels under salt stress. *Arthrobacter pascens* inoculation produces more proline in corn plants [104]. *Pseudomonas* spp. improved growth of

*Geobacillus* sp. Increased proline content [111]

Antioxidant enzymes and proline contents [107]

*Rhizobium* Osmotic regulation Increased chlorophyll

**PGPR strain Mechanism Improvement in crop References**

ACC deaminase Improved plant

*Pseudomonas* spp. EPS [101]

*Pseudomonas* spp. Osmotic regulation [103] *Proteus penneri* EPS [101]

Upregulation of aquaporin genes [94, 104,

*P. aeruginosa* IAA production, ACC deaminase, phosphate

solubilization, and biofilm formation

Antioxidant enzyme phosphate solubilization, osmotic regulation and antioxidant enzymes IAA production, ACC deaminase, phosphate solubilization, and biofilm formation

Facilitated gas exchange, osmoregulation, antioxidant enzymes, nutrient uptake, and downregulation of ABA biosynthesis

Improved K/Na ratio, polyphenol content, and

*B. amyloliquefaciens* Soluble sugar content and antioxidant enzymes Improved plant growth

proline concentration

*Bacillus* spp. Phosphate solubilization, osmotic regulation, and antioxidant enzymes

*Bacillus aquimaris* Chlorophyll content, osmotic regulation, and antioxidant enzymes

*Bacillus* IAA production, ACC deaminase, phosphate

solubilization, and biofilm formation

ACC deaminase Reduced ethylene

Ion toxicity, NOR, and nitrogenase activity Improved chlorophyll

EPS, antioxidant enzymes, and proline contents [101, 107]

growth

production

content Improved nutrition

and photosynthetic rate

and photosynthesis rate

[97–100]

[102]

105]

[102]

[106]

[97, 98]

[100]

[108]

[109]

[104]

[110]

[102]

[103]

*Pseudomonas syringae*, *P. fluorescens*

*Plant Stress Physiology*

*Pantoea agglomerans*, *Staphylococcus sciuri*, *Arthrobacter pascens*

*Gracilibacillus*, *Staphylococcus*, *Virgibacillus*, *Salinicoccus*, *Zhihengliuella*, *Brevibacterium*, *Oceanobacillus*, *Exiguobacterium*, *Arthrobacter*, and *Halomonas* spp.

*Serratia liquefaciens*

KM4

*Enterobacter aerogenes*, *Enterobacter* spp.

*Azospirillum brasilense*

*A. faecalis*, *A. brasilense* strains Ab-V5 and Ab-V6

*Azotobacter chroococcum*

*Rhizobium tropici* strain CIAT 899

*PGPR and their mechanisms for salt tolerance.*

**Table 1.**

**50**

against osmotic stress. A high level of VOCs in plants is a sign of activated selfprotective response against salt stress [120].

The VOCs produced by *Bacillus subtilis* triggered the gene of HKT1/K+ transporter and inhibited sodium ion influx through roots and eliminated salt stress. It also encouraged the glycine betaine synthesis that decreased the uptake of Na+ through roots and transported more nutrients toward shoot than during salt stress [120].

28-homo-brassinolide can lessen oxidative stress in salt-affected maize plants [129]. Priming with hydrogen peroxide improved activities of catalase ascorbate peroxidase and guaiacol peroxidase and increased seed germination percentage, under salt

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

Seeds of maize hybrid FH-810 were soaked in water (hydropriming), calcium chloride (2.2%, osmopriming), *Moringa* leaf extracts (MLE 3.3%, osmopriming),

osmopriming with CaCl2. Hormonal or osmopriming with MLE improved the yield performance at early planting primarily by increased crop growth, net assimilation rates, a leaf area index, and maintenance of green leaf area at maturity. Hormonal priming with SA and osmopriming with MLE were the most economical methods in enlightening early planted spring maize productivity by early seedling growth

**5.5 Application of molecular and genetic approaches such as MAS, selection,**

brane in salt-tolerant maize hybrid (SR 03) appeared as an important tolerance/ resistance trait. Turgor, cell wall acidification, and osmotic adjustment, in newly established salt-resistant maize hybrids, are a salt-resistant trait [48]. More abscisic acid accumulation in salt-resistant genotypes plays a role in osmotic adjustments under saline condition [39]. Salt-tolerant genotypes usually had lower sodium accumulation and more potassium to sodium and calcium to sodium ratio.

Sensitive genotypes had more sodium accumulation, suggesting that accumulation of sodium in shoots is a reliable screening parameter for salt tolerance/resistance in maize at early stages of growth [21]. However, higher sodium accumulation was observed in salt-tolerant Giza 2 roots than in salt-sensitive Trihybrid 321. Many other traits of maize plants such as growth rate, seedling weight, and photochemical efficiency should also be used for screening and breeding of

A proteomic approach is also used to recognize salt resistance-associated proteins in maize in breeding programs for markers to develop salt-tolerant/saltresistant genotypes. The use of physiological and molecular markers to recognize salt-resistant genotypes of maize is a reliable approach [132]. Sodium and soluble organic solute accumulations in roots were associated with maize salt resistance. More soluble organic solute and sodium accumulation in maize salt-tolerant genotype roots (BR5033) than in salt-sensitive genotype (BR5011) was reported. Hence, soluble organic solute and sodium accumulations in roots can be used as physiological markers to screen and isolate salt-resistant maize genotypes [15]. More total separated proteins (>80%) in severe saline stress in maize genotypes and 45 and

Maize is a polymorphic plant because of its cross-pollinated nature and genetic variations for salinity resistance. It is commonly a moderately salt-sensitive crop, but some salinity tolerant genotypes also exist. Tolerance in these genotypes occurs because of higher potassium and lower chloride and sodium cytoplasmic contents. Mass screening of maize genotypes is done to identify and isolate salt-tolerant germplasm for breeding purposes and to develop better performing genotypes. Screenings for salt tolerance or resistance are usually done at the early growth stages of maize plants [21]. Many plant characteristics are identified as salt-tolerant traits.

biological yield, 1000-grain weight, and harvest index were improved by seed priming. However, osmopriming with MLE and hormonal priming were more effective in these parameters. Hormonal priming at seedling stage increased the leaf

chlorophyll contents and decreased the electrical conductivity followed by

, hormonal priming), each for 18 h. Plant length,


stress condition in maize plants [73].

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

stimulation at low temperature [130].

Acidification of cell wall because of better H<sup>+</sup>

**and breeding approaches**

salt-tolerant crops [131].

**53**

and salicylic acid (SA, 50 mg L<sup>1</sup>

### **5.4 Seed priming**

Poor crop stands because of low seed germination rate in salt-affected areas are a challenge for the lucrative production of a crop. Maize seed germination rate is affected by toxic effects of chloride and sodium ions [25]. Seed priming helps to recover maize germination rate in salt-affected areas. Seed priming is a pre-sowing treatment either with water or any chemical of interest that boosts seed performance with a quicker and harmonized germination under sub-optimal and optimal conditions [121]. This is a physiological treatment under salinity in which seeds are moderately hydrated and radicle does not emerge [122]. Priming treatments include hydropriming with water, osmopriming with salts or osmolytes, and hormonal priming with hormones. Partial hydration is enough for the physiological process occurrence that is typical of the first stages of imbibition (pre-germinative metabolism) [123]. Under saline conditions germination rate improved by soaking maize seeds in water priming with water under salinity-enhanced maize seedling vigor index, germination index, final germination percentage, and seedling length, showing its potential as a seed invigoration technique under salinity for better maize performance [23].

Priming of seeds with salt solution enables them to break their dormancy and escape from disease-causing agents and competent seeds of weeds [124]. Priming seeds with NaCl significantly enhanced maize plant growth. Fresh and dry weights of roots and shoots were increased. Under salt stress, seed priming lessened the inhibitory effect of salt stress on maize seedling growth [125]. Priming with NaCl also increased plant height and yield and induced early emergence, more germination rate, more shoot length and dry weight, and more leaf chlorophyll, area, and number [126]. Seed halopriming with calcium chloride, sodium chloride, and potassium chloride was effective in mitigating the salt adversities on maize seed germination. Calcium chloride priming was most operative. Calcium, sodium, and potassium concentrations improved significantly in all parts of germinating seed. Most of the calcium was reserved in mesocotyl and seed, thus limiting its transference to radicles and plumules.

Seed priming with NaCl and CaCl2 had significant effects on germination rate, earlier growth, number of branches, cobs number, and yield. This increase in growth traits likely helps to reduce the competition for water and nutrients with associated improvements in seed yield. Sodium chloride seed priming increased shoot length, and calcium chloride seed priming increased root length. In vertisol soil, seed priming is preferred for improved crop yield and stand establishment, while in lithosol soils, seed priming is preferred for well germination of seed and increased cob number [124].

Other priming agents include thiamin, pyridoxine, and ascorbic acid, which not only improved the germination of pretreated seed but also improved seed growth and yield under salinity. Enhanced maize seedling biomass under saline conditions is reported by hormonal priming with chloro-ethyl-phosphonic acid, an ethylene releaser [127]. Salicylic acid application under saline conditions at the rate of 0.1 mM enhanced growth and development of plants [128]. Priming with 28-homo-brassinolide improved the antioxidative enzyme activities and lowered lipid peroxidation and increased concentration of protein, thus signifying that

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

28-homo-brassinolide can lessen oxidative stress in salt-affected maize plants [129]. Priming with hydrogen peroxide improved activities of catalase ascorbate peroxidase and guaiacol peroxidase and increased seed germination percentage, under salt stress condition in maize plants [73].

Seeds of maize hybrid FH-810 were soaked in water (hydropriming), calcium chloride (2.2%, osmopriming), *Moringa* leaf extracts (MLE 3.3%, osmopriming), and salicylic acid (SA, 50 mg L<sup>1</sup> , hormonal priming), each for 18 h. Plant length, biological yield, 1000-grain weight, and harvest index were improved by seed priming. However, osmopriming with MLE and hormonal priming were more effective in these parameters. Hormonal priming at seedling stage increased the leaf chlorophyll contents and decreased the electrical conductivity followed by osmopriming with CaCl2. Hormonal or osmopriming with MLE improved the yield performance at early planting primarily by increased crop growth, net assimilation rates, a leaf area index, and maintenance of green leaf area at maturity. Hormonal priming with SA and osmopriming with MLE were the most economical methods in enlightening early planted spring maize productivity by early seedling growth stimulation at low temperature [130].

### **5.5 Application of molecular and genetic approaches such as MAS, selection, and breeding approaches**

Maize is a polymorphic plant because of its cross-pollinated nature and genetic variations for salinity resistance. It is commonly a moderately salt-sensitive crop, but some salinity tolerant genotypes also exist. Tolerance in these genotypes occurs because of higher potassium and lower chloride and sodium cytoplasmic contents. Mass screening of maize genotypes is done to identify and isolate salt-tolerant germplasm for breeding purposes and to develop better performing genotypes. Screenings for salt tolerance or resistance are usually done at the early growth stages of maize plants [21]. Many plant characteristics are identified as salt-tolerant traits. Acidification of cell wall because of better H<sup>+</sup> -ATPase activity in the plasma membrane in salt-tolerant maize hybrid (SR 03) appeared as an important tolerance/ resistance trait. Turgor, cell wall acidification, and osmotic adjustment, in newly established salt-resistant maize hybrids, are a salt-resistant trait [48]. More abscisic acid accumulation in salt-resistant genotypes plays a role in osmotic adjustments under saline condition [39]. Salt-tolerant genotypes usually had lower sodium accumulation and more potassium to sodium and calcium to sodium ratio. Sensitive genotypes had more sodium accumulation, suggesting that accumulation of sodium in shoots is a reliable screening parameter for salt tolerance/resistance in maize at early stages of growth [21]. However, higher sodium accumulation was observed in salt-tolerant Giza 2 roots than in salt-sensitive Trihybrid 321. Many other traits of maize plants such as growth rate, seedling weight, and photochemical efficiency should also be used for screening and breeding of salt-tolerant crops [131].

A proteomic approach is also used to recognize salt resistance-associated proteins in maize in breeding programs for markers to develop salt-tolerant/saltresistant genotypes. The use of physiological and molecular markers to recognize salt-resistant genotypes of maize is a reliable approach [132]. Sodium and soluble organic solute accumulations in roots were associated with maize salt resistance. More soluble organic solute and sodium accumulation in maize salt-tolerant genotype roots (BR5033) than in salt-sensitive genotype (BR5011) was reported. Hence, soluble organic solute and sodium accumulations in roots can be used as physiological markers to screen and isolate salt-resistant maize genotypes [15]. More total separated proteins (>80%) in severe saline stress in maize genotypes and 45 and

against osmotic stress. A high level of VOCs in plants is a sign of activated self-

and inhibited sodium ion influx through roots and eliminated salt stress. It also encouraged the glycine betaine synthesis that decreased the uptake of Na+ through roots and transported more nutrients toward shoot than during salt stress [120].

challenge for the lucrative production of a crop. Maize seed germination rate is affected by toxic effects of chloride and sodium ions [25]. Seed priming helps to recover maize germination rate in salt-affected areas. Seed priming is a pre-sowing treatment either with water or any chemical of interest that boosts seed performance with a quicker and harmonized germination under sub-optimal and optimal conditions [121]. This is a physiological treatment under salinity in which seeds are moder-

ately hydrated and radicle does not emerge [122]. Priming treatments include

hydropriming with water, osmopriming with salts or osmolytes, and hormonal priming with hormones. Partial hydration is enough for the physiological process occurrence that is typical of the first stages of imbibition (pre-germinative metabolism) [123]. Under saline conditions germination rate improved by soaking maize seeds in water priming with water under salinity-enhanced maize seedling vigor index, germination index, final germination percentage, and seedling length, showing its potential as a seed invigoration technique under salinity for better maize performance [23]. Priming of seeds with salt solution enables them to break their dormancy and escape from disease-causing agents and competent seeds of weeds [124]. Priming seeds with NaCl significantly enhanced maize plant growth. Fresh and dry weights of roots and shoots were increased. Under salt stress, seed priming lessened the inhibitory effect of salt stress on maize seedling growth [125]. Priming with NaCl also increased plant height and yield and induced early emergence, more germination rate, more shoot length and dry weight, and more leaf chlorophyll, area, and number [126]. Seed halopriming with calcium chloride, sodium chloride, and potassium chloride was effective in mitigating the salt adversities on maize seed germination. Calcium chloride priming was most operative. Calcium, sodium, and potassium concentrations improved significantly in all parts of germinating seed. Most of the calcium was reserved in mesocotyl and seed, thus limiting its transfer-

Seed priming with NaCl and CaCl2 had significant effects on germination rate,

Other priming agents include thiamin, pyridoxine, and ascorbic acid, which not only improved the germination of pretreated seed but also improved seed growth and yield under salinity. Enhanced maize seedling biomass under saline conditions is reported by hormonal priming with chloro-ethyl-phosphonic acid, an ethylene releaser [127]. Salicylic acid application under saline conditions at the rate of 0.1 mM enhanced growth and development of plants [128]. Priming with 28-homo-brassinolide improved the antioxidative enzyme activities and lowered lipid peroxidation and increased concentration of protein, thus signifying that

earlier growth, number of branches, cobs number, and yield. This increase in growth traits likely helps to reduce the competition for water and nutrients with associated improvements in seed yield. Sodium chloride seed priming increased shoot length, and calcium chloride seed priming increased root length. In vertisol soil, seed priming is preferred for improved crop yield and stand establishment, while in lithosol soils, seed priming is preferred for well germination of seed and

The VOCs produced by *Bacillus subtilis* triggered the gene of HKT1/K+ transporter

Poor crop stands because of low seed germination rate in salt-affected areas are a

protective response against salt stress [120].

**5.4 Seed priming**

*Plant Stress Physiology*

ence to radicles and plumules.

increased cob number [124].

**52**

31% increase in root and shoot proteins under mild salinity showed differential regulation of proteins [58].

rate is reduced. At vegetative and reproductive stages, salinity affects photosynthesis, respiration, transpiration, stomatal and hormonal regulation, and water relation processes. These processes affect the growth pattern of plants and cause reduction in growth and yield. To mitigate the effects of salinity on maize crop, different management practices are used. Management by agronomic means, such as application of nutrients (through the application of biochar, compost, gypsum and nutrient fertilizers, etc.), either exogenously or as seed priming with different chemical and hormones, exogenous application of hormones, and growing of resistant cultivars, proved effective in reducing the adverse effects of salinity on maize crops. PGPR application mitigates the salinity stress by the production of different hormones, exopolypolysaccharides, or volatile organic compounds. Different genetic and molecular techniques are also used for inducing salinity tolerance by the insertion of tolerant genes in maize plants. For the future, more work on improved

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

Shazia Iqbal is thankful to Saline Agriculture Research Center, Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan, for the award of doctoral fellowships. Shazia Iqbal is giving special thanks to Dr. Sajid Hussain and Dr. Muhammad Ashraf for motivating him to write this chapter and providing guidance. The authors are also highly thankful to Muhammad Qayyaum, for contributing in the chapter write-up and providing them supporting material.

There is no conflict of interest among all the authors. All the authors revised and

genetic and molecular techniques is needed.

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

**Acknowledgements**

**Conflict of interest**

approved the chapter.

**55**

Transferring one or more salt-resistant genes from one species to another to insert required quantitative and qualitative characteristics is stated as the transgenic approach. This practice is much quicker than conventional breeding practices, and it warrants wanted genes induction without the addition of excess genes from the donor organism [133]. Improvements and advances in biotechnology and functional genomics have made it feasible to identify and distinguish salinity-tolerant genes that help to develop salt-resistant plants by the use of transgenic tactics (27).

By using the Flippase recombination enzyme P/Flippase recognition targetbased marker elimination system to eliminate the *als* gene [134]. Marker-free salttolerant transgenic maize is produced to improve the bio-safety of the environment. Under the saline condition, transgenic maize seed inserted with AtNHX1 gene and wild-type maize were planted. Wild-type maize plants withered, and upper leaves shriveled, whereas 56% of transgenic plants survived salinity up to the six-leaf stage. More grain yield, 1000-grain weight, was recorded in transgenic plants under saline condition than those under non-saline conditions. More potassium accumulation in root and shoot was observed in transgenic plants [134].

The sodium vacuolar compartmentation or cytoplasmic exclusion into the apoplasts through tonoplast sodium/hydrogen antiporters or plasma membrane is an adaptive mechanism to alleviate the adverse excess sodium effects in maize plants [26]. Under saline conditions, transgenic maize plants were better than wildtype plants because of higher hydrogen/sodium exchange rates in vesicles of tonoplast. Also, the efficient sodium vacuolar compartmentalization in cells of transgenic maize plants improved salt tolerance as well as the productivity of grain [134].

Salt stress boosted ZmNHX transcription which caused an increase in antiporters (sodium/hydrogen) of tonoplast in salt-resistant maize leaves by impounding sodium into vacuoles of the leaf to reduce sodium ion effects on the cytoplasm [135]. Transgenic maize plants with inserted sodium/hydrogen antiporter (OsNHX1) gene from *Oryza sativa* gave better yield than wild-type maize at 200 mM NaCl. Lower osmotic potential coupled with higher potassium and sodium contents in transgenic maize leaves was recorded under saline condition compared to wild maize [136].

The complementary DNA (cDNA) micro-array is an operative method for expression profile studies to assess differences and similarities under salinity stress in diverse patterns of expression. A cDNA macro-array with 190 maize expressed sequence tags persuaded by water stress was applied to cold stress, abscisic acid, and high salinity conditions. High salinity stress upregulated 41 sequence tags in roots and 36 sequence tags in leaves [137]. Quan et al. (2004) [138] introduced the betA gene encoding choline dehydrogenase (AtNHX1), which was inserted in maize line DH4866 from *Escherichia coli* to develop transgenic maize. This gene improved the biosynthesis of glycine betaine from choline under salinity and increased salt resistance in maize plants [139]. In conclusion, maize genotypes with externally inserted genes of betaine aldehyde dehydrogenase and vacuolar sodium/hydrogen antiporter, etc. performed better under salinity stress and can be used for inducing salt resistance in maize plants.

### **6. Conclusions**

Salinity stress poses a serious threat to maize. It affects the plant physiology and reduces growth and yield. Salinity affects the maize crop at different growth stages. Seed germination is the stage that is affected adversely by salinity, and germination *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

rate is reduced. At vegetative and reproductive stages, salinity affects photosynthesis, respiration, transpiration, stomatal and hormonal regulation, and water relation processes. These processes affect the growth pattern of plants and cause reduction in growth and yield. To mitigate the effects of salinity on maize crop, different management practices are used. Management by agronomic means, such as application of nutrients (through the application of biochar, compost, gypsum and nutrient fertilizers, etc.), either exogenously or as seed priming with different chemical and hormones, exogenous application of hormones, and growing of resistant cultivars, proved effective in reducing the adverse effects of salinity on maize crops. PGPR application mitigates the salinity stress by the production of different hormones, exopolypolysaccharides, or volatile organic compounds. Different genetic and molecular techniques are also used for inducing salinity tolerance by the insertion of tolerant genes in maize plants. For the future, more work on improved genetic and molecular techniques is needed.

### **Acknowledgements**

31% increase in root and shoot proteins under mild salinity showed differential

lation in root and shoot was observed in transgenic plants [134].

The sodium vacuolar compartmentation or cytoplasmic exclusion into the apoplasts through tonoplast sodium/hydrogen antiporters or plasma membrane is an adaptive mechanism to alleviate the adverse excess sodium effects in maize plants [26]. Under saline conditions, transgenic maize plants were better than wildtype plants because of higher hydrogen/sodium exchange rates in vesicles of tonoplast. Also, the efficient sodium vacuolar compartmentalization in cells of transgenic maize plants improved salt tolerance as well as the productivity of grain [134]. Salt stress boosted ZmNHX transcription which caused an increase in antiporters (sodium/hydrogen) of tonoplast in salt-resistant maize leaves by impounding sodium into vacuoles of the leaf to reduce sodium ion effects on the cytoplasm [135]. Transgenic maize plants with inserted sodium/hydrogen

antiporter (OsNHX1) gene from *Oryza sativa* gave better yield than wild-type maize at 200 mM NaCl. Lower osmotic potential coupled with higher potassium and sodium contents in transgenic maize leaves was recorded under saline condition

The complementary DNA (cDNA) micro-array is an operative method for expression profile studies to assess differences and similarities under salinity stress in diverse patterns of expression. A cDNA macro-array with 190 maize expressed sequence tags persuaded by water stress was applied to cold stress, abscisic acid, and high salinity conditions. High salinity stress upregulated 41 sequence tags in roots and 36 sequence tags in leaves [137]. Quan et al. (2004) [138] introduced the betA gene encoding choline dehydrogenase (AtNHX1), which was inserted in maize line DH4866 from *Escherichia coli* to develop transgenic maize. This gene improved the biosynthesis of glycine betaine from choline under salinity and increased salt resistance in maize plants [139]. In conclusion, maize genotypes with externally inserted genes of betaine aldehyde dehydrogenase and vacuolar sodium/hydrogen antiporter, etc. performed better under salinity stress and can be used for inducing

Salinity stress poses a serious threat to maize. It affects the plant physiology and reduces growth and yield. Salinity affects the maize crop at different growth stages. Seed germination is the stage that is affected adversely by salinity, and germination

Transferring one or more salt-resistant genes from one species to another to insert required quantitative and qualitative characteristics is stated as the transgenic approach. This practice is much quicker than conventional breeding practices, and it warrants wanted genes induction without the addition of excess genes from the donor organism [133]. Improvements and advances in biotechnology and functional genomics have made it feasible to identify and distinguish salinity-tolerant genes that help to develop salt-resistant plants by the use of transgenic tactics (27). By using the Flippase recombination enzyme P/Flippase recognition targetbased marker elimination system to eliminate the *als* gene [134]. Marker-free salttolerant transgenic maize is produced to improve the bio-safety of the environment. Under the saline condition, transgenic maize seed inserted with AtNHX1 gene and wild-type maize were planted. Wild-type maize plants withered, and upper leaves shriveled, whereas 56% of transgenic plants survived salinity up to the six-leaf stage. More grain yield, 1000-grain weight, was recorded in transgenic plants under saline condition than those under non-saline conditions. More potassium accumu-

regulation of proteins [58].

*Plant Stress Physiology*

compared to wild maize [136].

salt resistance in maize plants.

**6. Conclusions**

**54**

Shazia Iqbal is thankful to Saline Agriculture Research Center, Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan, for the award of doctoral fellowships. Shazia Iqbal is giving special thanks to Dr. Sajid Hussain and Dr. Muhammad Ashraf for motivating him to write this chapter and providing guidance. The authors are also highly thankful to Muhammad Qayyaum, for contributing in the chapter write-up and providing them supporting material.

### **Conflict of interest**

There is no conflict of interest among all the authors. All the authors revised and approved the chapter.

*Plant Stress Physiology*

### **Author details**

Shazia Iqbal1 , Sajid Hussain2 \*, Muhammad Abdul Qayyaum<sup>3</sup> , Muhammad Ashraf<sup>4</sup> and Saifullah<sup>5</sup>

**References**

1995;**22**:875-884

1023

Service; 2005

**57**:1025-1043

1993;**20**:425-437

**57**

[1] Flowers TJ, Yeo A. Breeding for salinity resistance in crops. Where next? Australian Journal of Plant Physiology.

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

[11] Munns R, Tester M. Mechanisms of salinity tolerance. Annual Review of Plant Biology. 2008;**59**:651-681

[12] Hussain M, Park HW, Farooq M, Jabran H, Lee DJ. Morphological and physiological basis of salt resistance in different rice genotypes. International Journal of Agriculture and Biology.

[13] Davenport R, James RA, Zakrisson-Plogander A, Tester M, Munns R. Control of sodium transport in durum wheat. Journal of Plant Physiology.

[14] Quintero JM, Fournier JM, Benlloch M. Na<sup>+</sup> accumulation in shoot is related

sunflower plants but not in plants with a normal K<sup>+</sup> status. Journal of Plant Physiology. 2007;**164**:60-67

to water transport in K<sup>+</sup> starved

[15] de Azevedo Neto AD, Prisco JT, Eneas J, de Abreu CEB, Gomes-Filho E. Effect of salt stress on antioxidative enzymes and lipid peroxidation in leaves

and roots of salt-tolerant and salt sensitive maize varieties. Environmental and Experimental Botany. 2006;**56**:87-94

[16] Neubert AB, Zörb C, Schubert S. Expression of vacuolar Na+ /H+ antiporters (ZmNHX) and Na+ exclusion in roots of maize (*Zea mays* L.) genotypes with improved salt resistance. In: Li CJ et al., editors. Plant Nutrition for Food Security, Human Health and Environmental Protection. Bejing, China: Tsinghua University Press; 2005. pp. 544-545

[17] Hichem H, Mounir D, Naceur EA. Differential responses of two maize (*Zea mays* L.) varieties to salt stress: Changes on polyphenols composition of foliage and oxidative damages. Industrial Crops

[18] Schubert S. Advances in alleviating growth limitations of maize under salt

and Products. 2009;**30**:144-151

2013;**15**:113-118

2005;**137**:807-818

[2] Munns R. Comparative physiology of salt and water stress. Plant, Cell and Environment. 2002;**25**:239-250

[3] Rengasamy P. World salinization with emphasis on Australia. Journal of Experimental Botany. 2006;**57**:1017-

[4] FAO. Global Network on Integrated Soil Management for Sustainable Use of Salt-Affected Soils. Rome, Italy: FAO Land and Plant Nutrition Management

[5] Munns R. Genes and salt tolerance:

[6] Munns R, James RA, Läuchli A. Approaches to increasing the salt tolerance of wheat and other cereals. Journal of Experimental Botany. 2006;

[7] Munns R, Sharp RE. Involvement of abscisic acid in controlling plant growth

Australian Journal of Plant Physiology.

[9] Menezes-Benavente L, Kernodle SP, Margis-Pinheiro M, Scandalios JG. Salt induced antioxidant metabolism defenses in maize (*Zea mays* L.) seedlings. Redox Report. 2004;**9**:29-36

[10] Flowers TJ, Flowers SA. Why does salinity pose such a difficult problem for plant breeders? Agricultural Water Management. 2005;**78**:15-24

in soils of low water potential.

[8] Fortmeier R, Schubert S. Salt tolerance ofmaize (*Zea mays* L.): The role of sodium exclusion. Plant, Cell and Environment. 1995;**18**:1041-1047

Bringing them together. New Phytologist. 2005;**167**:645-663

1 Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan

2 State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, Zhejiang, China

3 Department of Soil and Environmental Sciences, Faculty of Agricultural Sciences, Ghazi University, Dera Ghazi Khan, Punjab, Pakistan

4 Department of Soil Science, Bahauddin Zakariya University, Multan, Pakistan

5 Department of Environmental Health, College of Public Health, Imam Abdulrehman Bin Faisal University, Dammam, Saudi Arabia

\*Address all correspondence to: hussainsajid@caas.cn

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

### **References**

[1] Flowers TJ, Yeo A. Breeding for salinity resistance in crops. Where next? Australian Journal of Plant Physiology. 1995;**22**:875-884

[2] Munns R. Comparative physiology of salt and water stress. Plant, Cell and Environment. 2002;**25**:239-250

[3] Rengasamy P. World salinization with emphasis on Australia. Journal of Experimental Botany. 2006;**57**:1017- 1023

[4] FAO. Global Network on Integrated Soil Management for Sustainable Use of Salt-Affected Soils. Rome, Italy: FAO Land and Plant Nutrition Management Service; 2005

[5] Munns R. Genes and salt tolerance: Bringing them together. New Phytologist. 2005;**167**:645-663

[6] Munns R, James RA, Läuchli A. Approaches to increasing the salt tolerance of wheat and other cereals. Journal of Experimental Botany. 2006; **57**:1025-1043

[7] Munns R, Sharp RE. Involvement of abscisic acid in controlling plant growth in soils of low water potential. Australian Journal of Plant Physiology. 1993;**20**:425-437

[8] Fortmeier R, Schubert S. Salt tolerance ofmaize (*Zea mays* L.): The role of sodium exclusion. Plant, Cell and Environment. 1995;**18**:1041-1047

[9] Menezes-Benavente L, Kernodle SP, Margis-Pinheiro M, Scandalios JG. Salt induced antioxidant metabolism defenses in maize (*Zea mays* L.) seedlings. Redox Report. 2004;**9**:29-36

[10] Flowers TJ, Flowers SA. Why does salinity pose such a difficult problem for plant breeders? Agricultural Water Management. 2005;**78**:15-24

[11] Munns R, Tester M. Mechanisms of salinity tolerance. Annual Review of Plant Biology. 2008;**59**:651-681

[12] Hussain M, Park HW, Farooq M, Jabran H, Lee DJ. Morphological and physiological basis of salt resistance in different rice genotypes. International Journal of Agriculture and Biology. 2013;**15**:113-118

[13] Davenport R, James RA, Zakrisson-Plogander A, Tester M, Munns R. Control of sodium transport in durum wheat. Journal of Plant Physiology. 2005;**137**:807-818

[14] Quintero JM, Fournier JM, Benlloch M. Na<sup>+</sup> accumulation in shoot is related to water transport in K<sup>+</sup> starved sunflower plants but not in plants with a normal K<sup>+</sup> status. Journal of Plant Physiology. 2007;**164**:60-67

[15] de Azevedo Neto AD, Prisco JT, Eneas J, de Abreu CEB, Gomes-Filho E. Effect of salt stress on antioxidative enzymes and lipid peroxidation in leaves and roots of salt-tolerant and salt sensitive maize varieties. Environmental and Experimental Botany. 2006;**56**:87-94

[16] Neubert AB, Zörb C, Schubert S. Expression of vacuolar Na+ /H+ antiporters (ZmNHX) and Na+ exclusion in roots of maize (*Zea mays* L.) genotypes with improved salt resistance. In: Li CJ et al., editors. Plant Nutrition for Food Security, Human Health and Environmental Protection. Bejing, China: Tsinghua University Press; 2005. pp. 544-545

[17] Hichem H, Mounir D, Naceur EA. Differential responses of two maize (*Zea mays* L.) varieties to salt stress: Changes on polyphenols composition of foliage and oxidative damages. Industrial Crops and Products. 2009;**30**:144-151

[18] Schubert S. Advances in alleviating growth limitations of maize under salt

**Author details**

*Plant Stress Physiology*

, Sajid Hussain2

Ghazi University, Dera Ghazi Khan, Punjab, Pakistan

\*Address all correspondence to: hussainsajid@caas.cn

provided the original work is properly cited.

\*, Muhammad Abdul Qayyaum<sup>3</sup>

1 Institute of Soil and Environmental Sciences, University of Agriculture,

2 State Key Laboratory of Rice Biology, China National Rice Research Institute,

3 Department of Soil and Environmental Sciences, Faculty of Agricultural Sciences,

4 Department of Soil Science, Bahauddin Zakariya University, Multan, Pakistan

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

5 Department of Environmental Health, College of Public Health, Imam

Abdulrehman Bin Faisal University, Dammam, Saudi Arabia

, Muhammad Ashraf<sup>4</sup>

Shazia Iqbal1

and Saifullah<sup>5</sup>

**56**

Faisalabad, Pakistan

Hangzhou, Zhejiang, China

stress. In: The Proceedings of the International Plant Nutrition Colloquium XVI; Department of Plant Sciences, UC Davis; 2009

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[20] Jafar MZ, Farooq M, Cheema MA, Afzal I, Basra SMA, Wahid MA, et al. Improving the performance of wheat by seed priming under saline conditions. Journal of Agronomy and Crop Science. 2012;**198**:38-45

[21] Eker S, Comertpay G, Konuskan O, Ulger AC, Ozturk L, Cakmak I. Effect of salinity stress on dry matter production and ion accumulation in hybrids maize varieties. Turkish Journal of Agriculture and Forestry. 2006;**30**:365-373

[22] Gunes A, Inal A, Alpaslam M, Erslan F, Bagsi EG, Cicek N. Salicylic acid induced changes on some physiological parameters symptomatic for oxidative stress and mineral nutrition inmaize (*Zea mays* L.) grown under salinity. Journal of Plant Physiology. 2007;**164**: 728-736

[23] Janmohammadi M, Dezfuli PM, Sharifzadeh F. Seed invigoration techniques to improve germination and early growth of inbred line of maize under salinity and drought stress. General and Applied Plant Physiology. 2008;**34**:215-226

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Biology Journal of North America. 2011;

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

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[47] Abdullah Z, Khan MA, Flowers TJ. Causes of sterility in seed set of rice under salinity stress. Journal of

Agronomy and Crop Science. 2001;**187**:

[48] Schubert S, Neubert A, Schierholt A, Sumer A, Zorb C. Development of salt resistant maize hybrids: The combination of physiological strategies using conventional breeding methods. Plant Science. 2009;**177**:196-202

[49] Hiyane R, Hiyane S, Tang AC, Boyer JS. Sucrose feeding reverses

Adaptation responses in C4

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**2**:907-920

341-345

**39**:1513-1522

membrane H+

**116**:483-505

321-326

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584-588

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2008;**34**:215-226

2005;**88**:223-271

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Colloquium XVI; Department of Plant

germination of soybean seeds. Seed Science and Technolog. 2003;**31**:715-725

[26] Goldsworthy. Calcium and salinity. Annals of Applied Biology. 1994;**4**:1-6

[27] Hasegawa PM, Bressan RA, Zhu JK, Bohnert HJ. Plant cellular and molecular

[28] Shannon MC, Grieve CM, Francois LE. Whole plant response to salinity. In:

Environment Interactions. New York:

[29] Rios-Gonzalez K, Erdei L, Lips SH. The activity of antioxidant enzymes in maize and sunflower seedlings as affected by salinity and different nitrogen sources. Plant Science. 2002;

[30] Akram M, Ashraf MY, Ahmad R, Rafiq M, Iqbal AIJ. Allometry and yield components of maize (*Zea mays* L.) hybrids to various potassium levels under saline conditions. Archives of Biological Sciences. 2010;**62**:1053-1061

[31] Qu C, Liu C, Gong X, Li C, Hong M, Wang L, et al. Impairment of maize seedling photosynthesis caused by a combination of potassium deficiency and salt stress. Environmental and Experimental Botany. 2012;**75**:134-141

[32] Pitann B, Kranz T, Mühling KH. The apoplastic pH and its significance in adaptation to salinity in corn (*Zea mays* L.): Comparison of fluorescence microscopy and pH-sensitive

microelectrodes. Plant Science. 2009;

[33] El Sayed HESA. Influence of salinity

photosynthetic activity and cytological studies of *Zea mays*,L. plant using hydrogel polymer. Agriculture and

stress on growth parameters,

response to high salinity. Annual Review of Plant Physiology and Plant Molecular Biology. 2000;**51**:463-499

Wilkinson RE, editor. Plant-

Dekker; 1994. pp. 199-244

**162**:923-930

**176**:497-504

[19] Kaya C, Tuna AL, Okant AM. Effect of foliar applied kinetin and indole acetic acid on maize plants grown under saline conditions. Turkish Journal of Agriculture and Forestry. 2010;**34**:529-

[20] Jafar MZ, Farooq M, Cheema MA, Afzal I, Basra SMA, Wahid MA, et al. Improving the performance of wheat by seed priming under saline conditions. Journal of Agronomy and Crop Science.

[21] Eker S, Comertpay G, Konuskan O, Ulger AC, Ozturk L, Cakmak I. Effect of salinity stress on dry matter production and ion accumulation in hybrids maize varieties. Turkish Journal of Agriculture

[22] Gunes A, Inal A, Alpaslam M, Erslan F, Bagsi EG, Cicek N. Salicylic acid induced changes on some physiological parameters symptomatic for oxidative stress and mineral nutrition inmaize (*Zea mays* L.) grown under salinity. Journal of Plant Physiology. 2007;**164**:

[23] Janmohammadi M, Dezfuli PM, Sharifzadeh F. Seed invigoration techniques to improve germination and early growth of inbred line of maize under salinity and drought stress. General and Applied Plant Physiology.

[24] Ashraf M, Foolad MR. Pre-sowing seed treatment-a shotgun approach to improve germination growth and crop yield under saline and none-saline conditions. Advances in Agronomy.

[25] Khaje-Hosseini M, Powell AA, Bingham IJ. The interaction between salinity stress and seed vigour during

and Forestry. 2006;**30**:365-373

[34] Wakeel A, Sümer A, Hanstein S, Yan F, Schubert S. In vitro effect of Na<sup>+</sup> / K<sup>+</sup> ratios on the hydrolytic and pumping activity of the plasma membrane H-ATPase from maize (*Zea mays* L.) and sugar beet (*Beta vulgaris* L.) shoot. Plant Physiology and Biochemistry. 2011;**49**: 341-345

[35] Cramer GR, Epstein E, Lauchli A. Kinetics of root elongation of maize in response to short term exposure to NaCl and elevated calcium concentration. Journal of Experimental Botany. 1988; **39**:1513-1522

[36] Spanswick RM. Electrogenic ion pumps. Annual Review of Plant Physiology. 1981;**32**:267-289

[37] Hager A. Role of the plasma membrane H+ -ATPase in auxin-induced elongation growth: Historical and new aspects. Journal of Plant Research. 2003; **116**:483-505

[38] Cosgrove DJ. Loosening of plant cell walls by expansins. Nature. 2000;**407**: 321-326

[39] De Costa W, Zorb C, Hartung W, Schubert S. Salt resistance is determined by osmotic adjustment and abscisic acid in newly developedmaize hybrids in the first phase of salt stress. Physiologia Plantarum. 2007;**131**:311-321

[40] Karimi G, Ghorbanli M, Heidari H, Khavarinejad RA, Assareh MH. The effects of NaCl on growth, water relations, osmolytes and ion content in Kochia prostrate. Biologia Plantarum. 2005;**49**:301-304

[41] Turan MA, Elkarim AHA, Taban N, Taban S. Effect of salt stress on growth and ion distribution and accumulation in shoot and root of maize plant. African Journal of Agricultural Research. 2010;**5**: 584-588

[42] Yasmeen A, Basra SMA, Farooq M, Rehman H, Hussain N, Athar HR. Exogenous application of moringa leaf extract modulates the antioxidant enzyme system to improve wheat performance under saline conditions. Plant Growth Regulation. 2013;**69**: 225-233

[43] Hu Y, Burucs Z, Tucher SV, Schmidhalter U. Short-term effects of drought and salinity on mineral nutrient distribution along growing leaves of maize seedlings. Environmental and Experimental Botany. 2007;**60**:268-275

[44] Gadalla AM, Hamdy A, Galal YGM, Aziz HAA, Mohamed MAA. Evaluation of maize growth under salinity stress and N application strategies using stable nitrogen isotope. African Crop Science Conference Proceedings. 2007;**8**:1553- 1562

[45] Omoto E, Taniguchi M, Miyake H. Adaptation responses in C4 photosynthesis of maize under salinity. Journal of Plant Physiology. 2012;**169**: 469-477

[46] Gong XL, Liu C, Zhou M, Luo LY, Wang L, Wang Y, et al. Oxidative damages of maize seedlings caused by combined stress of potassium deficiency and salt stress. Plant and Soil. 2011;**340**: 443-452

[47] Abdullah Z, Khan MA, Flowers TJ. Causes of sterility in seed set of rice under salinity stress. Journal of Agronomy and Crop Science. 2001;**187**: 25-32

[48] Schubert S, Neubert A, Schierholt A, Sumer A, Zorb C. Development of salt resistant maize hybrids: The combination of physiological strategies using conventional breeding methods. Plant Science. 2009;**177**:196-202

[49] Hiyane R, Hiyane S, Tang AC, Boyer JS. Sucrose feeding reverses

shade-induced kernel losses in maize. Annals of Botany. 2010;**106**:395-403

[50] Lohaus G, Hussmann M, Pennewiss K, Schneider H, Zhu JJ, Sattelmacher B. Solute balance of a maize (*Zea mays* L.) source leaf as affected by salt treatment with special emphasis on phloem retranslocation and ion leaching. Journal of Experimental Botany. 2000;**51**:1721- 1732

[51] Serraj R, Sinclair TR. Osmolyte accumulation: Can it really help increase crop yield under drought conditions? Plant, Cell and Environment. 2002;**25**: 333-341

[52] Yeo AR, Kramer D, Lauchli A, Gullasch J. Ion distribution in saltstressed mature *Zea mays* roots in relation to ultrastructure and retention of sodium. Journal of Experimental Botany. 1977;**28**:17-29

[53] Alberico GL, Cramer GR. Is the salt tolerance of maize related to sodium exclusion? I. Preliminary screening of seven cultivars. Journal of Plant Nutrition. 1993;**16**:2289-2303

[54] Isla R, Aragues R. Yield and plant ion concentrations in maize (*Zea mays* L.) subject to diurnal and nocturnal saline sprinkler irrigations. Field Crops Research. 2010;**116**:175-183

[55] Gill SS, Tuteja N. Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants. Plant Physiology and Biochemistry. 2010;**48**:909-930

[56] Zhu JK. Plant salt tolerance. Trends in Plant Science. 2001;**6**:66-71

[57] Mittler R. Oxidative stress, antioxidants and stress tolerance. Trends in Plant Science. 2002;**7**:405-410

[58] Zörb C, Schmitt S, Neeb A, Karl S, Linder M, Schubert S. The biochemical reaction of maize (*Zea mays* L.) to salt

stress is characterized by a mitigation of symptoms and not by a specific adaptation. Plant Science. 2004;**167**:91- 100

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pretreatment in maize. Plant Physiology

[74] Hussein MM, Balbaa LK, Gaballah MS. Salicylic acid and salinity effects on growth of maize plants. Research Journal of Agricultural and Biological

[75] Monowara K, Shuvo AR, Salam TB, Rahman H, Tareq MBS, Tareq MS. Effect of organic amendments on soil salinity and the growth of maize (*Zea mays* L.). Plant Science. 2019;**6**(2):106-

[76] Oo AN, Iwai CB, Saenjan P. Soil properties and maize growth in saline and nonsaline soils using cassavaindustrial waste compost and vermicompost with or without earthworms. Land Degradation and Development. 2015;**26**(3):300-310

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Cunningham SC, Jackson WR, Patti AF. Does biochar improve establishment of tree seedlings in saline sodic soils? Land Degradation and Development. 2016;**27**:

Conocarpus biochar induces changes in soil nutrient availability and tomato growth under saline irrigation. Pedosphere. 2016;**26**:27-38

[80] Uzoma KC, Inoue M, Andry H, Fujimaki H, Zahoor A, Nishihara E.

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[69] El-Sharkawy HM, Shehata SA, Eisa SS, Kishk ET, Khafaga HS, Abd. El-Naby AS. Foliar application of thidiazuron, potassium chloride and boron with early cultivation date elevated growth and productivity of hybrid corn grown under adverse conditions. International Journal of Environment. 2017;**06**(2):31-

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*Plant Stress Physiology*

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adaptation. Plant Science. 2004;**167**:91-

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amylacea from the Lluta Valley (Arica-Chile) tolerates salinity stress when high

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(2):1323-1327

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100

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[51] Serraj R, Sinclair TR. Osmolyte accumulation: Can it really help increase crop yield under drought conditions? Plant, Cell and Environment. 2002;**25**:

[52] Yeo AR, Kramer D, Lauchli A, Gullasch J. Ion distribution in saltstressed mature *Zea mays* roots in relation to ultrastructure and retention of sodium. Journal of Experimental

[53] Alberico GL, Cramer GR. Is the salt tolerance of maize related to sodium exclusion? I. Preliminary screening of seven cultivars. Journal of Plant Nutrition. 1993;**16**:2289-2303

[54] Isla R, Aragues R. Yield and plant ion concentrations in maize (*Zea mays* L.) subject to diurnal and nocturnal saline sprinkler irrigations. Field Crops

[55] Gill SS, Tuteja N. Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants. Plant Physiology and Biochemistry.

[56] Zhu JK. Plant salt tolerance. Trends

[58] Zörb C, Schmitt S, Neeb A, Karl S, Linder M, Schubert S. The biochemical reaction of maize (*Zea mays* L.) to salt

in Plant Science. 2001;**6**:66-71

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Research. 2010;**116**:175-183

2010;**48**:909-930

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Botany. 1977;**28**:17-29

1732

333-341

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[67] El-Dissoky RA, Ebtsam M, Morsy, El-Shazly MA. Beneficial effect of potassium fertilization and yeast strains on maize plants grown on salt affected soil. Journal of Soil Science and Agricultural Engineering. 2013;**4**(9): 827-842

[68] Hussain Z, Khattak RA, Fareed I, Irshad M, Mahmood Q. Interaction of phosphorus and potassium on maize (*Zea mays* L.) in saline-sodic soil. Journal of Agricultural Science. 2015;**7**(3):1916- 9760

[69] El-Sharkawy HM, Shehata SA, Eisa SS, Kishk ET, Khafaga HS, Abd. El-Naby AS. Foliar application of thidiazuron, potassium chloride and boron with early cultivation date elevated growth and productivity of hybrid corn grown under adverse conditions. International Journal of Environment. 2017;**06**(2):31- 41

[70] Mahmoodabadi M, Yazdanpanah N, Sinobas LR, Pazira E, Neshat A. Reclamation of calcareous saline sodic soil with di\_erent amendments (I): Redistribution of soluble cations within the soil profile. Agricultural Water Management Journal. 2013;**120**:30-38

[71] Wang L, Sun X, Li S, Zhang T, Zhang W, Zhai P. Application of organic amendments to a coastal saline soil in North China: Effects on soil physical and chemical properties and tree growth. PLoS One. 2014;**9**:e89185

[72] Jishi Z, Jiang X, Xue Y, Li Z, Yu B, Xu L, et al. Closing yield gaps through soil improvement for maize production in coastal saline soil. Agronomy. 2019;**9**: 573

[73] Gondim FA, Gomes-Filho E, Costa JH, Alencar NLM, Prisco JT. Catalase plays a key role in salt stress acclimation induced by hydrogen peroxide pretreatment in maize. Plant Physiology and Biochemistry. 2012;**56**:62-71

[74] Hussein MM, Balbaa LK, Gaballah MS. Salicylic acid and salinity effects on growth of maize plants. Research Journal of Agricultural and Biological Sciences. 2007;**3**:321-328

[75] Monowara K, Shuvo AR, Salam TB, Rahman H, Tareq MBS, Tareq MS. Effect of organic amendments on soil salinity and the growth of maize (*Zea mays* L.). Plant Science. 2019;**6**(2):106- 111

[76] Oo AN, Iwai CB, Saenjan P. Soil properties and maize growth in saline and nonsaline soils using cassavaindustrial waste compost and vermicompost with or without earthworms. Land Degradation and Development. 2015;**26**(3):300-310

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[87] Kaya C, Ashraf M, Dikilitas M, Tuna AL. Alleviation of salt stress-induced

adverse effects on maize plants by exogenous application of indoleacetic acid (IAA) and inorganic nutrients—A field trial. Australian Journal of Crop Science. 2013;**7**(2):249-254

Deciphering *Staphylococcus sciuri* SAT-17

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

[101] Naseem H, Bano A. Role of plant growth-promoting rhizobacteria and their exopolysaccharide in drought tolerance of maize. Journal of Plant Interactions. 2014;**9**:689-701

[102] Aslam F, Ali B. Halotolerant bacterial diversity associated with *Suaeda fruticosa* (L.) Forssk. Improved growth of maize under salinity stress.

[103] Bano A, Fatima M. Salt tolerance in *Zea mays* L. following inoculation with rhizobium and pseudomonas. Biology and Fertility of Soils. 2009;**45**(4):405-

[104] Ullah S, Bano A. Isolation of plantgrowth-promoting rhizobacteria from rhizospheric soil of halophytes and their impact on maize (*Zea mays* L.) under induced soil salinity. Canadian Journal of Microbiology. 2015;**61**:307-313

[105] Gond SK, Torres MS, Bergen MS, Helsel Z, White JFJ. Induction of salt tolerance and up-regulation of aquaporin genes in tropical corn by rhizobacterium *Pantoea agglomerans*. Letters in Applied Microbiology. 2015;

[106] El-Esawi MA, Alaraidh IA, Alsahli AA, Alzahrani SA, Ali HM, Alayafi AA,

[107] Fukami J, de la Osa C, Ollero FJ, Megías M, Hungria M. Coinoculation of maize with *Azospirillum brasilense* and *Rhizobium tropici* as a strategy to mitigate salinity stress. Functional Plant

[108] Rojas-Tapias D, Moreno-Galván A, Pardo-Díaz S, Obando M, Rivera D, Bonilla R. Effect of inoculation with

et al. Serratia liquefaciens KM4 improves salt stress tolerance in maize by regulating redox potential, ion homeostasis, leaf gas exchange and stress-related gene expression. International Journal of Molecular

Sciences. 2018;**19**:3310

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413

**60**:392-399

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induced saline environment. Journal of Applied Microbiology. 2018;**124**:

[96] Yang J, Kloepper JW, Ryu CM. Rhizosphere bacteria help plants tolerate abiotic stress. Trends in Plant

[97] Nadeem SM, Zahir ZA, Naveed M, Arshad M. Preliminary investigations on inducing salt tolerance in maize through

[98] Nadeem SM, Zahir ZA, Naveed M, Arshad M. Rhizobacteria containing ACC-deaminase confer salt tolerance in maize grown on salt-affected fields. Canadian Journal of Microbiology.

[99] Zafar-ul-Hye M, Farooq HM, Zahir ZA, Hussain M, Hussain A. Application

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Science. 2009;**14**(1):1-4

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**63**

of ACC-deaminase containing rhizobacteria with fertilizer improvesmaize production under drought and salinity stress. International Journal of Agriculture and Biology.

inoculation with rhizobacteria containing ACC deaminase activity. Canadian Journal of Microbiology. 2007;

1566-1579

**53**:1141-1149

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[88] Darra BL, Saxena SN. Role of IAA on the mineral composition of maize crop under various osmotic stressed conditions. Plant and Soil. 1973;**38**:657-

[89] Tuna AL, Kaya C, Dikilitas HD. The combined effects of gibberellic acid and salinity on some antioxidant enzyme activities, plant growth parameters and nutritional status in maize plants. Environmental and Experimental

Science. 2013;**7**(2):249-254

Botany. 2008;**62**(1):1-9

[90] Rashad RT, Rashad AH. A

Science. 2014;**59**(1):89-94

foxtail millet in a semi-arid

Microbiology. 2018;**8**:2580

88-111

161-172

[91] Niu X, Song L, Xiao Y, Ge W. Drought-tolerant plant growth-

promoting rhizobacteria associated with

agroecosystem and their potential in alleviating drought stress. Frontiers in

[92] Banaei-Asl F, Bandehagh A, Uliaei ED, Farajzadeh D, Sakata K, Mustafa G, et al. Proteomic analysis of canola root inoculated with bacteria under salt stress. Journal of Proteomics. 2015;**124**:

[93] Wang Q, Dodd IC, Belimov AA, Jiang F. Rhizosphere bacteria containing 1-aminocyclopropane-1-carboxylate deaminase increase growth and

photosynthesis of pea plants under salt stress by limiting Na+ accumulation. Functional Plant Biology. 2016;**43**(2):

[94] Akram MS, Shahid M, Tariq M, Azeem M, Javed MT, Saleem S, et al.

comparison study on the effect of some growth regulators on the nutrients content of maize plant under salinity conditions. Annals of Agricultural

661

[81] Lashari MS, Ye MSY, Ji H, Li L, Kibue GW, Lu H, et al. Biochar-manure

[82] Rita L, Vitti C. Use of organic amendments to reclaim saline and sodic soils: A review. Arid Land Research and

[83] Lomin SN, Krivosheev DM, Steklov MY, Arkhipov DV, Osolodkin DI, Schmulling TR, et al. Plant membrane assays with cytokinin receptors underpin the unique role of free cytokinin bases as biologically active ligands. Journal of Experimental Botany.

[84] Tomaz R, Mukesh J, Marina D, Prem C. Spatial and temporal profiles of

accumulation in developing caryopses of maize. Annals of Botany. 2011;**107**(7):

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[86] Salama FM, Awadalla AA. The effect of different kinetin application

parameters of two crop plants grown under salinity stress. Phyton. 1987;**27**:

[87] Kaya C, Ashraf M, Dikilitas M, Tuna AL. Alleviation of salt stress-induced

methods on some chlorophyll

Management. 2019;**33**(1):1-21

2015;**66**(7):1851-1863

1235-1245

2017;**40**:169-180

181-193

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cytokinin biosynthesis and

compost in conjunction with pyroligneous solution alleviated salt stress and improved leaf bioactivity of maize in a saline soil from Central China: A 2-year field experiment. Journal of the Science of Food and Agriculture. 2015;**95**:1321-1327

*Plant Stress Physiology*

212

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[96] Yang J, Kloepper JW, Ryu CM. Rhizosphere bacteria help plants tolerate abiotic stress. Trends in Plant Science. 2009;**14**(1):1-4

[97] Nadeem SM, Zahir ZA, Naveed M, Arshad M. Preliminary investigations on inducing salt tolerance in maize through inoculation with rhizobacteria containing ACC deaminase activity. Canadian Journal of Microbiology. 2007; **53**:1141-1149

[98] Nadeem SM, Zahir ZA, Naveed M, Arshad M. Rhizobacteria containing ACC-deaminase confer salt tolerance in maize grown on salt-affected fields. Canadian Journal of Microbiology. 2009;**55**(11):1302-1309

[99] Zafar-ul-Hye M, Farooq HM, Zahir ZA, Hussain M, Hussain A. Application of ACC-deaminase containing rhizobacteria with fertilizer improvesmaize production under drought and salinity stress. International Journal of Agriculture and Biology. 2014;**16**:591-596

[100] Zerrouk IZ, Benchabane M, Khelifi L, Yokawa K, Ludwig-Müller J, Baluska F. A Pseudomonas strain isolated from date-palm rhizospheres improves root growth and promotes root formation in maize exposed to salt and aluminum stress. Journal of Plant Physiology. 2016; **191**:111-119

[101] Naseem H, Bano A. Role of plant growth-promoting rhizobacteria and their exopolysaccharide in drought tolerance of maize. Journal of Plant Interactions. 2014;**9**:689-701

[102] Aslam F, Ali B. Halotolerant bacterial diversity associated with *Suaeda fruticosa* (L.) Forssk. Improved growth of maize under salinity stress. Agronomy. 2018;**8**:131

[103] Bano A, Fatima M. Salt tolerance in *Zea mays* L. following inoculation with rhizobium and pseudomonas. Biology and Fertility of Soils. 2009;**45**(4):405- 413

[104] Ullah S, Bano A. Isolation of plantgrowth-promoting rhizobacteria from rhizospheric soil of halophytes and their impact on maize (*Zea mays* L.) under induced soil salinity. Canadian Journal of Microbiology. 2015;**61**:307-313

[105] Gond SK, Torres MS, Bergen MS, Helsel Z, White JFJ. Induction of salt tolerance and up-regulation of aquaporin genes in tropical corn by rhizobacterium *Pantoea agglomerans*. Letters in Applied Microbiology. 2015; **60**:392-399

[106] El-Esawi MA, Alaraidh IA, Alsahli AA, Alzahrani SA, Ali HM, Alayafi AA, et al. Serratia liquefaciens KM4 improves salt stress tolerance in maize by regulating redox potential, ion homeostasis, leaf gas exchange and stress-related gene expression. International Journal of Molecular Sciences. 2018;**19**:3310

[107] Fukami J, de la Osa C, Ollero FJ, Megías M, Hungria M. Coinoculation of maize with *Azospirillum brasilense* and *Rhizobium tropici* as a strategy to mitigate salinity stress. Functional Plant Biology. 2018;**45**:328-339

[108] Rojas-Tapias D, Moreno-Galván A, Pardo-Díaz S, Obando M, Rivera D, Bonilla R. Effect of inoculation with

plant growth-promoting bacteria (PGPB) on amelioration of saline stress in maize (*Zea mays*). Applied Soil Ecology. 2012;**61**:264-272

[109] Chen L, Liu Y, Wu G, Veronican Njeri K, Shen Q, Zhang N, et al. Induced maize salt tolerance by rhizosphere inoculation of *Bacillus amyloliquefaciens* SQR9. Physiologia Plantarum. 2016;**158**: 34-44

[110] Li H, Jiang X. Inoculation with plant growth-promoting bacteria (PGPB) improves salt tolerance of maize seedling. Russian Journal of Plant Physiology. 2017;**64**(2):235-241

[111] Abdelkader AF, Esawy MA. Case study of a biological control: *Geobacillus caldoxylosilyticus* (IRD) contributes to alleviate salt stress in maize (*Zea mays* L.) plants. Acta Physiologiae Plantarum. 2011;**33**(6):2289

[112] Krasensky J, Jonak C. Drought, salt, and temperature stress-induced metabolic rearrangements and regulatory networks. Journal of Experimental Botany. 2012;**63**(4):1593-1608

[113] Halo BA, Khan AL, Waqas M, Al-Harras A, Hussain J, Ali L, et al. Endophytic bacteria (*Sphingomonas* sp. LK11) and gibberellin can improve *Solanum lycopersicum* growth and oxidative stress under salinity. Journal of Plant Interactions. 2015;**10**(1):117-125

[114] Kim K, Jang YJ, Lee SM, Oh BT, Chae JC, Lee KJ. Alleviation of salt stress by *Enterobacter* sp. EJ01 in tomato and *Arabidopsis* is accompanied by upregulation of conserved salinity responsive factors in plants. Molecular Cell. 2014;**37**(2):109

[115] Abd El-Ghany TM, Masrahi YS, Mohamed A, Abboud A, Alawlaqi MM, et al. Maize (*Zea mays* L.) growth and metabolic dynamics with plant growthpromoting rhizobacteria under salt stresses. Journal of Plant Pathology and Microbiology. 2015;**6**:305

[116] Upadhyay S, Singh J, Singh D. Exopolysaccharide-producing plant growth promoting rhizobacteria under salinity condition. Pedosphere. 2011;**21** (2):214-222

priming in maize (*Zea mays*): Prospect for salt tolerance. African Journal of Biotechnology. 2017;**16**(5):209-223

*DOI: http://dx.doi.org/10.5772/intechopen.92213*

*The Response of Maize Physiology under Salinity Stress and Its Coping Strategies*

in maize: Effects, resistance mechanisms, and management. A review. Agronomy for Sustainable Development. 2015;**35**:461-481

19-54

[133] Gosal SS, Wani SH, Kang MS. Biotechnology and drought tolerance. Journal of Crop Improvement. 2009;**23**:

[134] Li B, Li N, Duan X, Wei A, Yang A, Zhang J. Generation of marker-free transgenic maize with improved salt

[135] Pitann B, Mohamed A-K, Neubert

antiporters of newly developed maize (*Zea mays*) hybrids contribute to salt resistance during the second phase of salt stress. Journal of Plant Nutrition and

/H+

tolerance using the FLP/FRT recombination system. Journal of Biotechnology. 2010;**145**:206-213

AB, Schubert S. Tonoplast Na<sup>+</sup>

Soil Science. 2013;**176**:148-156

[136] Chen M, Chen Q-J, Niu X-G, Zhang R, Lin H-Q, Xu C-Y, et al. Expression of OsNHX1 gene in maize confers salt tolerance and promotes plant growth in the field. Plant, Soil and

Environment. 2007;**53**:490-498

M, Dong Z, et al. Comparative

a water stress-specific cDNA

2006;**170**:1125-1132

**166**:141-149

2004;**46**:854-861

[137] Zheng J, Zhao J, Zhang J, Fu J, Gou

expression profiles of maize genes from

macroarray in response to high salinity, cold or abscisic acid. Plant Science.

[138] Quan R, Shang M, Zhang H, Zhao Y, Zhang J. Improved chilling tolerance by transformation with betaA gene for the enhancement of glycinebetaine synthesis in maize. Plant Science. 2004;

[139] Yin XY, Yang AF, Zhang KW, Zhang JR. Production and analysis of transgenic maize with improved salt tolerance by the introduction of AtNHX1 gene. Acta Botanica Sinica.

[125] Abraha B, Yohannes G. The role of seed priming in improving seedling growth of maize (*Zea mays* L.) under salt stress at field conditions. Agricultural

[126] Farahbakhsh H, Saiid MS. Effect of seed priming with NaCl on maize germination under different saline conditions. African Journal of Agricultural Research. 2011;**6**:6095-

[127] Carvalho RF, Piotto FA, Schmidt D, Peters LP, Monteiro CC, Azevedo RA. Seed priming with hormones does not alleviate induced oxidative stress in maize seedlings subjected to salt stress. Journal of Scientific Agriculture. 2011;

[128] Khodary SEA. Effect of salicylic acid on the growth, photosynthesis and carbohydrate metabolism in saltstressed maize plants. International Journal of Agriculture and Biology.

[129] Arora N, Bhardwaj R, Sharma P, Arora HK. 28-Homobrassinolide alleviates oxidative stress in salt treated maize (*Zea mays* L.) plants. Brazilian Journal of Plant Physiology. 2008;**20**:

[130] Rehman H, Hassan I, Basra SMA, Afzal I, Farooq M, Wakeel A, et al. Seed priming improves early seedling vigor, growth and productivity of spring maize. Journal of Integrative Agriculture. 2015;**14**(9):1745-1754

[131] Giaveno CD, Ribeiro RV, Souza GM, de Oliveira RF. Screening of tropical maize for salt stress tolerance.

[132] Muhammad F, Hussain M, Wakeel A, Kadambot H, Siddique M. Salt stress

Crop Breeding and Applied Biotechnology. 2007;**7**:304-313

Sciences. 2013;**4**(12):666-672

6099

**68**:598-602

2004;**6**:5-8

153-157

**65**

[117] Miller G, Suzuki N, Ciftci-Yilmaz S, Mittler R. Reactive oxygen species homeostasis and signalling during drought and salinity stresses. Plant, Cell and Environment. 2010;**33**(4):453-467

[118] Rossi F, De Philippis R. Role of cyanobacterial exopolysaccharides in phototrophic biofilms and in complex microbial mats. Life. 2015;**5**(2):1218- 1238

[119] Zhang H, Kim MS, Sun Y, Dowd SE, Shi H, Paré PW. Soil bacteria confer plant salt tolerance by tissue-specific regulation of the sodium transporter HKT1. Molecular Plant-Microbe Interactions. 2008;**21**(6):737-744

[120] Timmusk S, El-Daim IAA, Copolovici L, Tanilas T, Kännast A, Behers L, et al. Drought-tolerance of wheat improved by rhizosphere bacteria from harsh environments: Enhanced biomass production and reduced emissions of stress volatiles. PLoS One. 2014;**9**(5):e96086

[121] Sivritepe N, Sivritepe HO, Eris A. The effects of NaCl priming on salt tolerance in melon seedlings grown under saline conditions. Scientia Horticulturae (Amsterdam). 2003;**97**: 229-237

[122] Ibrahim EA. Seed priming to alleviate salinity stress in germinating seeds. Journal of Plant Physiology. 2016; **192**:38-46

[123] Paparella S, Araujo SS, Rossi G, Wijayasinghe M, Carbonera D, Balestrazzi A. Seed priming: State of the art and new perspectives. Plant Cell Reports. 2015;**34**:1281-1293

[124] Gebreslassie GB, Qufa CA. Plant physiological stimulation by seeds salt *The Response of Maize Physiology under Salinity Stress and Its Coping Strategies DOI: http://dx.doi.org/10.5772/intechopen.92213*

priming in maize (*Zea mays*): Prospect for salt tolerance. African Journal of Biotechnology. 2017;**16**(5):209-223

plant growth-promoting bacteria (PGPB) on amelioration of saline stress in maize (*Zea mays*). Applied Soil

[116] Upadhyay S, Singh J, Singh D. Exopolysaccharide-producing plant growth promoting rhizobacteria under salinity condition. Pedosphere. 2011;**21**

[117] Miller G, Suzuki N, Ciftci-Yilmaz S, Mittler R. Reactive oxygen species homeostasis and signalling during drought and salinity stresses. Plant, Cell and Environment. 2010;**33**(4):453-467

[118] Rossi F, De Philippis R. Role of cyanobacterial exopolysaccharides in phototrophic biofilms and in complex microbial mats. Life. 2015;**5**(2):1218-

[119] Zhang H, Kim MS, Sun Y, Dowd SE, Shi H, Paré PW. Soil bacteria confer plant salt tolerance by tissue-specific regulation of the sodium transporter HKT1. Molecular Plant-Microbe Interactions. 2008;**21**(6):737-744

[120] Timmusk S, El-Daim IAA, Copolovici L, Tanilas T, Kännast A, Behers L, et al. Drought-tolerance of wheat improved by rhizosphere bacteria from harsh environments: Enhanced biomass production and reduced emissions of stress volatiles. PLoS One.

[121] Sivritepe N, Sivritepe HO, Eris A. The effects of NaCl priming on salt tolerance in melon seedlings grown under saline conditions. Scientia Horticulturae (Amsterdam). 2003;**97**:

[122] Ibrahim EA. Seed priming to alleviate salinity stress in germinating seeds. Journal of Plant Physiology. 2016;

[123] Paparella S, Araujo SS, Rossi G, Wijayasinghe M, Carbonera D,

Reports. 2015;**34**:1281-1293

Balestrazzi A. Seed priming: State of the art and new perspectives. Plant Cell

[124] Gebreslassie GB, Qufa CA. Plant physiological stimulation by seeds salt

2014;**9**(5):e96086

229-237

**192**:38-46

(2):214-222

1238

[109] Chen L, Liu Y, Wu G, Veronican Njeri K, Shen Q, Zhang N, et al. Induced maize salt tolerance by rhizosphere inoculation of *Bacillus amyloliquefaciens* SQR9. Physiologia Plantarum. 2016;**158**:

[110] Li H, Jiang X. Inoculation with plant growth-promoting bacteria (PGPB) improves salt tolerance of maize seedling. Russian Journal of Plant

Physiology. 2017;**64**(2):235-241

2011;**33**(6):2289

[111] Abdelkader AF, Esawy MA. Case study of a biological control: *Geobacillus caldoxylosilyticus* (IRD) contributes to alleviate salt stress in maize (*Zea mays* L.) plants. Acta Physiologiae Plantarum.

[112] Krasensky J, Jonak C. Drought, salt,

metabolic rearrangements and regulatory networks. Journal of Experimental Botany. 2012;**63**(4):1593-1608

[113] Halo BA, Khan AL, Waqas M, Al-Harras A, Hussain J, Ali L, et al. Endophytic bacteria (*Sphingomonas* sp. LK11) and gibberellin can improve *Solanum lycopersicum* growth and oxidative stress under salinity. Journal of Plant Interactions. 2015;**10**(1):117-125

[114] Kim K, Jang YJ, Lee SM, Oh BT, Chae JC, Lee KJ. Alleviation of salt stress by *Enterobacter* sp. EJ01 in tomato and

[115] Abd El-Ghany TM, Masrahi YS, Mohamed A, Abboud A, Alawlaqi MM, et al. Maize (*Zea mays* L.) growth and metabolic dynamics with plant growthpromoting rhizobacteria under salt stresses. Journal of Plant Pathology and

*Arabidopsis* is accompanied by upregulation of conserved salinity responsive factors in plants. Molecular

Cell. 2014;**37**(2):109

Microbiology. 2015;**6**:305

**64**

and temperature stress-induced

Ecology. 2012;**61**:264-272

*Plant Stress Physiology*

34-44

[125] Abraha B, Yohannes G. The role of seed priming in improving seedling growth of maize (*Zea mays* L.) under salt stress at field conditions. Agricultural Sciences. 2013;**4**(12):666-672

[126] Farahbakhsh H, Saiid MS. Effect of seed priming with NaCl on maize germination under different saline conditions. African Journal of Agricultural Research. 2011;**6**:6095- 6099

[127] Carvalho RF, Piotto FA, Schmidt D, Peters LP, Monteiro CC, Azevedo RA. Seed priming with hormones does not alleviate induced oxidative stress in maize seedlings subjected to salt stress. Journal of Scientific Agriculture. 2011; **68**:598-602

[128] Khodary SEA. Effect of salicylic acid on the growth, photosynthesis and carbohydrate metabolism in saltstressed maize plants. International Journal of Agriculture and Biology. 2004;**6**:5-8

[129] Arora N, Bhardwaj R, Sharma P, Arora HK. 28-Homobrassinolide alleviates oxidative stress in salt treated maize (*Zea mays* L.) plants. Brazilian Journal of Plant Physiology. 2008;**20**: 153-157

[130] Rehman H, Hassan I, Basra SMA, Afzal I, Farooq M, Wakeel A, et al. Seed priming improves early seedling vigor, growth and productivity of spring maize. Journal of Integrative Agriculture. 2015;**14**(9):1745-1754

[131] Giaveno CD, Ribeiro RV, Souza GM, de Oliveira RF. Screening of tropical maize for salt stress tolerance. Crop Breeding and Applied Biotechnology. 2007;**7**:304-313

[132] Muhammad F, Hussain M, Wakeel A, Kadambot H, Siddique M. Salt stress

in maize: Effects, resistance mechanisms, and management. A review. Agronomy for Sustainable Development. 2015;**35**:461-481

[133] Gosal SS, Wani SH, Kang MS. Biotechnology and drought tolerance. Journal of Crop Improvement. 2009;**23**: 19-54

[134] Li B, Li N, Duan X, Wei A, Yang A, Zhang J. Generation of marker-free transgenic maize with improved salt tolerance using the FLP/FRT recombination system. Journal of Biotechnology. 2010;**145**:206-213

[135] Pitann B, Mohamed A-K, Neubert AB, Schubert S. Tonoplast Na<sup>+</sup> /H+ antiporters of newly developed maize (*Zea mays*) hybrids contribute to salt resistance during the second phase of salt stress. Journal of Plant Nutrition and Soil Science. 2013;**176**:148-156

[136] Chen M, Chen Q-J, Niu X-G, Zhang R, Lin H-Q, Xu C-Y, et al. Expression of OsNHX1 gene in maize confers salt tolerance and promotes plant growth in the field. Plant, Soil and Environment. 2007;**53**:490-498

[137] Zheng J, Zhao J, Zhang J, Fu J, Gou M, Dong Z, et al. Comparative expression profiles of maize genes from a water stress-specific cDNA macroarray in response to high salinity, cold or abscisic acid. Plant Science. 2006;**170**:1125-1132

[138] Quan R, Shang M, Zhang H, Zhao Y, Zhang J. Improved chilling tolerance by transformation with betaA gene for the enhancement of glycinebetaine synthesis in maize. Plant Science. 2004; **166**:141-149

[139] Yin XY, Yang AF, Zhang KW, Zhang JR. Production and analysis of transgenic maize with improved salt tolerance by the introduction of AtNHX1 gene. Acta Botanica Sinica. 2004;**46**:854-861

**67**

**Chapter 4**

**Abstract**

ssp. Maritima)

*Shahzad Ahmed and Alvina Gul*

scarce times and salinity amelioration.

**1.1 Origin, history, and adaptation**

**1. Introduction**

Production and Salinity Tolerance

of Fodder Beet (*Beta vulgaris* L.

*Sami Ullah Khan, Zulfiqar Ali Gurmani, Waseem Ahmed,* 

Fodder beet (*Beta vulgaris* L. ssp. maritima) belongs to the Amaranthaceae family. It was introduced first in the Europe and then to USA in 1800 and is currently being grown under cool environmental conditions of the world. It can be cultivated at temperature ranging from 8°C to 25°C. Both shoots and roots of fodder beet can be used as a feed for livestock. In the face of changing climate, there is a dire need to find out climate-resilient crops in new niches that can fulfill the growing needs of farming communities. In this context, fodder beet could be a good option for growers having sizable marginal as well as salt-affected soils. The chapter discusses in detail the efficient salinity-tolerance mechanism of fodder beet that enables it to survive under moderate salinity. Selective ion uptake mechanism, efficient antioxidant defensive mechanism and osmoregulation by accumulation of compatible solutes enable it to thrive well under saline environment. Hence, fodder beet is a relatively salt-tolerant crop that can be successfully grown on normal, marginal as well as salt-affected soils to fulfill the fodder requirements of livestock in fodder-

**Keywords:** fodder beet, salinity, compatible solutes, salt tolerant crop, livestock

Fodder beet (*Beta vulgaris* L. ssp. maritima) is known to have been originated in Mesopotamia (Middle East) and ancient Greece in 500 BC chiefly used as animal fodder [1]. It belongs to the Amaranthaceae family, which consists of about 105 genera separated into 1400 species, mainly herbaceous dicotyledonous plants [2]. *It was introduced firstly in Europe and then to USA in 1800 and is currently grown under cool environmental conditions of the world, mainly Northern America and New Zealand at 600–1000 m altitudes in the tropics*. *It can be cultivated at a temperature ranging from* 8 to 25°C. However, frost can damage the seedlings below −3°C. Suitable soil pH for beet cultivation is greater than 6.5 but acid soils are not adequate for beet growth. The crop is relatively salt tolerant and can also be cultivated with brackish water. It is drought tolerant and could be grown

### **Chapter 4**
