*2.3.1 Salinity in the growth and development of the mother plant*

The growth conditions experienced by the mother plants affect the quality and behavior of the next generation, expressed in the physiological quality, size, and weight of the seed [8, 68]. Salinity stress during germination and early seedling growth affects crop growth and yield [83]. Shoot and root length are strongly affected by increased salinity of a stressed seed [79].

Stomatal conductance, transpiration rate, and CO2 concentration in cells decrease under salt stress affecting growth, development, and crop yield [38]. Ionic toxicity causes metabolic imbalance and protein synthesis in saline soils and also limits plant growth due to the replacement of K<sup>+</sup> by Na<sup>+</sup> ; biochemical reactions and conformational changes induced by Na<sup>+</sup> and Cl<sup>−</sup> occur in proteins [84–87]. In saline soils, the high concentration of toxic ions in the rhizosphere is a function of their level of interaction with mineral nutrients. The interaction of salts can result in considerable nutritional deficit and imbalance. The ionic imbalance in conditions of high soil salinity occurs in the cells due to the excessive accumulation of Na<sup>+</sup> and Cl<sup>−</sup> ions that reduces the uptake of other mineral nutrients such as K<sup>+</sup> , Ca2+, and Mn2+ [88]. The adverse effects of salinity on plant development are most profound during the reproductive phase and lead to cell cycle imbalance and differentiation. In trees, salt restricts the cell cycle by interfering with cyclin and kinase activities within the plant system and thus produces fewer cells in the meristem, limiting growth [89].

Faced with this type of stress, crops have complex physiological and biochemical response mechanisms and various factors, both inherent to the genotype, and to the morphology and physiology of the plant, influence these adverse conditions [87, 90, 91]. Proline, as an important osmoprotectant, contributes to osmotic adjustment, protecting enzymes from oxidative damage in saline conditions [67, 87]. The accumulation of other compounds such as soluble sugar facilitates the maintenance of turgor and/or the protection of the macromolecular structure against the destabilizing effects of decreased water activity [92].

In case of quinoa, considered facultative halophyte, it can grow at a high level of salinity up to 18 dS m−1, without having a decrease in seed yield and biomass with a salinity of up to 6 dS m−1 [11]. The accumulation of endogenous hormones at different NaCl concentrations during plant growth may be related to seed development and salt tolerance of brown and black Suaeda sauce seeds. These characteristics may help the species ensure seedling establishment and population succession in variable saline environments [93].

#### *2.3.2 Salinity effect on seed germination*

Seed germination is regulated by internal factors, such as proteins, plant hormones (gibberellins/ABA, ethylene, and auxin), related genes (maturation genes and genes regulating hormones and epigenetics), nonenzymatic processes, seed age, size of the seed, and structural components of the seed, including (endosperm and seed coat) and by external factors, such as soil moisture, light, salinity, temperature, acidity, and nutrients [94–96]. Plants subjected to salinization are affected from germination to more advanced stages of development; the presence of salts interferes with the water potential of the soil, reducing the potential gradient between the soil and the seed, restricting water absorption [70, 74, 97, 98]. When the osmotic potential of the solution is lower than that of the embryonic cells, the speed, the percentage of germination, and the formation of seedlings are reduced [64, 71, 72].

Changing the physiological activity of the seed can affect the protein content and therefore the nutrient reserve in the endosperm or cotyledons, affecting the processes of seed germination and with low vigor indices, as occurs in species such as broccoli and cauliflower. Absorption of excess Na<sup>+</sup> and Cl− ions from soils creates ionic stress and causes toxicity that contributes to the disruption of biochemical processes, including nucleic and protein metabolism, energy production, and respiration [99].

Salinity can negatively influence germination or delay seed germination by decreasing amounts of seed germination stimulants, such as GA, increasing amounts of ABA, and altering membrane permeability and water behavior in the seed. Delay in water uptake and a decrease in α-amylase activity with an increase in NaCl concentration may be the main reasons for delayed germination time [70].

Under saline conditions, the physiological quality of the seeds in each cultivar or species can have variable behaviors (**Table 3**). The grass species ryegrass (*Lolium perenne* L.); barley (*Hordeum vulgare* L.); vetch (*Vicia sativa* L.) and *Cicer arietinum* L.; alfalfa (*Medicago sativa* L.); oats (*Avena sativa* L.) under conditions of 0, 50 and 100 mM NaCl show a germination percentage greater than 70% [80]. However, the germination rate of all species is reduced to 200 and 400 mM respectively, producing an important reduction in water absorption levels compared to seeds not subjected to salt stress [80]. In the case of barley, as it is a highly salt-tolerant crop, it can germinate at 400 mM of NaCl, reaching 24% germination with a reduction of 76% compared to the control. The reduction in the percentage of seed germination is due to the reduction in germination with the increase in NaCl concentrations, it is the result of a decrease or delay in the absorption of water in the seeds due to the toxic effects that the ions exert on them since the functions of the membrane and the cell wall of the embryo are affected; as a result of the plasmatic membranes permeability reduction, an accumulation of external ions and loss of cytosolic solutes [100].

Some species are salt dependent, prolonged absence of NaCl in the soil inhibits seed development, results in lower seed quality and thus limits progeny seedling growth as is the case of *Suaeda salsa*, typical annual extreme halophytic herb with succulent leaves, develops well and produces high-quality seeds when is grown under high salinity conditions [5].

### **3. Conclusion**

High-quality seed is the main input to obtain high crop yields; the physical, physiological, genetic, and sanitary quality of the seeds depend on the genetic material

used in sowing, management of the mother plant, temperature conditions, humidity, solar intensity, and soil fertility. The environmental effects of seed production are complex, the environment of the mother plant has a significant influence on seed traits, including seed size, dormancy, and germination. Seed germination is regulated by internal factors, such as proteins, plant hormones (gibberellins/ABA, ethylene, and auxin), related genes (maturation genes and hormone and epigenetic regulatory genes), nonenzymatic processes, seed age, size of the seed and structural changes, seed components, including (endosperm and seed coat), and by external factors, such as soil moisture, light, salinity, temperature, pH, and nutrients.

During the seed formation stage, the final quality of the seed can be affected by water, mineral, salinity, and temperature deficiencies. Water deficiency during grain filling, flowering, or pod formation reduces germination potential and seed vigor and damage can be greater when water deficit is complemented by high temperatures, causing the production of a high proportion of small seeds due to loss of nonstructural starch and sugar reserve. At the level of the mother plant, water deficit affects the growth and development of the mother plant, due to the decrease in the activity of the photosynthetic enzyme galactinol synthase.

The increase in the internal temperature of the plant causes the closure of the stomata and causes damage to the seed due to the decrease in the thermoregulatory effect of water, which influences seed germination. The decrease in photosynthesis at high temperatures reduces the flow of the substances produced toward the seed; in this condition they are used to sustain respiration, creating an imbalance in the stage of spike formation or seed filling, and affecting the quality and size of the seeds. Consequently, the cumulative effects of these changes often result in poor growth and reduced plant productivity.

High temperatures affect the development of gametes and the process of double fertilization and therefore the number of seeds formed. It also affects pollen production and viability, stigma receptivity, pollen germination, and pollen tube elongation. In high-temperature conditions, there is a higher production of superoxides (ROS) reducing the metabolic activity of the seed necessary for the germination process.

High salinity levels reduce the germination potential of seeds or may retard the germination process or affect plant growth by interfering with seed germination as well as enzyme activity and unbalance mitosis mainly in glycophytic plants. Some plant species of the halophytic type can tolerate high levels of salinity, but the levels of germination and vigor of the seeds can be affected in the absence of salts. Most cultivated plants are salt-sensitive glycophytes. In contrast, halophytic species such as quinoa (*C. quinoa* Willd.) and *Suaeda aralocapsica* are capable of reducing stomatal density when grown under hypersalinity conditions. Quinoa can tolerate and function without a significant decrease in seed yield and biomass in salinity up to 6 d S m −1, in halophytes, the absence.

*Water Stress, Heat, and Salinity in the Physiological Quality of the Seeds DOI: http://dx.doi.org/10.5772/intechopen.107006*
