Introductory Chapter: Inevitable Cytogenetic, Genetic, and Epigenetic Changes Contributing to Phenotypic Plasticity for Plant Defence Mechanisms in Dynamic Environmental Conditions

*Josphert Ngui Kimatu*

## **1. Introduction**

Plants are currently encountering many changes in the environment, which are being brought about by human activities due to increasing population demands and land fragmentations. Studies show that over 50% of the regions on the earth are expected to suffer from water scarcity by 2050 [1, 2]. These activities include pollutions, increase in temperature, lack of pollinators and dispersal mechanisms. The observed morphological changes in plants are due to changes in gene expressions [3]. These gene expression changes do not involve permanent changes in the DNA sequences; otherwise, the species would either become extinct or modified to be another. However, these changes have been identified in the functional genomics and names as mainly epigenetic. Epigenetic variations can be used to indicate the degree of plant responses due to environmental stresses. Plant adaptations in stress conditions can be induced by long-term or short-term stress exposures [4]. In stressful conditions, plants use three main strategies to survive. They either tolerate, resist, or escape but also employ stress recovery mechanisms after the stress challenging environmental conditions [5–7].

Climate change coupled with other environmental pressures is making the rate of formation of new plant gene combinations to seem quite slow compared with the occurrence of the environmental pressures [8]. Plants employ processes such as stress avoidance via regulating characteristics such as leaf structure, root growth, flowering patterns, seed development, so as to optimize prevailing morphological and physiological processes.

## **2. The relationship between environmental stress and epigenetic variability**

Plants have to endure adverse environmental conditions at all times. This is because plants are sessile and do not physically escape stresses by changing locations. Plants defend themselves by employing epigenetic mechanisms [9]. Experiments have been done using plants of similar genetic compositions, which have grown in varied environmental conditions. For example, dandelion plants were grown in conditions of high salinity, low nutrients, and pathogenic induced by jasmonic acid or salicylic acid showed DNA methylation polymorphisms [10]. To confirm the results, the experimental control plants showed less epigenetic variations. Thus, epigenetic changes are important abiotic plant defense biomarkers in plant defense. Plants employ various mechanisms to sense environmental changes and then initiate epigenetic gene expression responses to enable adjustments in such situations [11]. More research should be done because, to date, only one transgenic maize cultivar has been commercialized among so many crop plants [6, 12].

### **3. The relationship between plant metabolism and epigenetic variability**

Metabolism is defined as all chemical reactions in a cell that occur to maintain life. The level of acceptable rate of metabolism is determined by the number of environmental and cellular resources available for the plant. For example, water is a major plant resource that if there is water stress, much metabolism activity is shut down. This is done mainly via cytosine DNA hypermethylation. The mechanism that most plants use to respond to water stress is the expression of the abscisic acid (ABA) genes. For example, studies using repeated dehydration steps upregulated several ABA-induced genes in the model plant *Arabidopsis thaliana* [13, 14], while review studies by [4], suggested that changes in DNA methylation served as regulatory mechanisms affecting gene expression responses to drought stress. Previously, transposon mobility, activation of methyltransferase, and siRNA-mediated methylation have been implicated in phenotype variation in stress conditions [15].

### **4. The relationship between plant microbes, pests, abiotic stresses, and epigenetic variability**

Plants establish biotic relationships, which are either beneficial or harmful. The beneficial relationships include those with the bacteria *Rhizobia*, *mycorrhiza*, with insect pollinators and seed dispersers. The harmful relationships involve viral, fungal, protozoan, bacterial pathogens and other competitors [16]. Thus, studies show that infection of plants by RNA viruses triggers epigenetic changes. For example, plants have been observed to recognize inserted viral double-strand RNA molecules and then inducing DCL2 and DCL4 for their degradation into siRNAs [17]. Other complex mechanisms to deal with single-stranded RNA (ssRNA) have also been observed. In this process, the genomes of ssRNA viruses are first converted into dsRNA molecules by RNA-dependent RNA polymerases and then the DCL family endoribonucleases act on the dsRNA,

Studies in *Arabidopsis* showed that an infection by a bacterial pathogen such as *Pseudomonas syringae* pv. *tomato* (Pst) elicited a defense response in plants that was suppressed by bacterial virulence factors. The data showed that cytosine DNA methylation pattern changes of some genes are associated with plant defense mechanisms. For example, *de novo* methylation can occur in a process where previously unmethylated DNA cytosine residues are methylated. This leads to new DNA methylation patterns being formed [18]. Other DNA expression related modifications include acetylation, phosphorylation, biotinylation, sumoylation, and ubiquitination at specific amino acid residues [19]. Furthermore, epigenetic changes were related to transcriptional changes of defense-related root genes [20–22].

#### *Introductory Chapter: Inevitable Cytogenetic, Genetic, and Epigenetic Changes Contributing… DOI: http://dx.doi.org/10.5772/intechopen.102991*

Plants trigger gene expressions to survive all kinds of biotic and abiotic stresses. However, if the stress occurs in a short term, the plant can trigger rapid epigenetic changes to survive. Cassava plants have been observed to rapidly produce hydrogen cyanide (HCN) in case of biotic environmental disturbance and also could mistake a long-term abiotic stress and continually produce HCN to defend itself [23, 24]. Plants such as *Arabidopsis* when subjected to several cycles of water stress were found to spring back to normal metabolism faster than plants that experienced the water stress for the first time [25]. This is because even the mechanisms employed by plants to overcome various kinds of stresses are metabolically expensive and can drain plant resources. Plants transmit the epigenetic changes to the next generation in a phenomenon called transgenerational inheritable epigenetic changes or epimutations [25–27]. Extremes of most essential substances for plant growth and development can trigger extensive DNA methylations. For example, water stress can interfere with almost all metabolic processes, and if not checked, the plant can die. Furthermore, studies have shown essential trace elements such as Cu2+ and Cr3+ caused gross changes in DNA methylation only at high concentrations. Studies on *Laguncularia racemosa* showed that same plant species can be in different environmental conditions and be genetically similar but be varied epigenetically [28]. The mechanisms underlying these epigenetic changes remain largely unknown.

Other questions that linger are, for example, if plant epigenetic plasticity could be the cause invasive plants to be established in new habitats or it is new habitats that caused epigenetic variability? [4, 29]. More information is still needed in deciphering the significance of epigenetic mechanisms in influencing activities of specific plant growth regulators (PGRs) in the regulation of plant drought resistance and plant-microbiome interactions [6]. Studies have already been done on various tolerance-enhancing PGRs such as agonists, polyamines, antioxidants, and osmoprotectants [30–32] while further studies on the model grass *Brachypodium distachyon* gave more light on the genetic, epigenetic, and cytogenetic polymorphism mechanisms in plants. This is because the plant has a small genome and has fully been sequenced. It has a fast growth and is also almost cosmopolitan. This makes it to portray a great deal of observable phenotypic plasticity [33]. Statistical modeling can be used to establish the relationship between genetic distance and epigenetic variability or phenotypic variance and additive genetic effects [4].

#### **5. Conclusions and prospects**

Recent studies have confirmed the perceived relationship between epigenetic variations and environmental adaptations. The phenomenon of phenotypic plasticity as guided by varied epigenetic expressions enables plants to survive in changing environments while maintaining DNA sequence integrity. An understanding of the correction between genetic distances, epigenetic variations, heritability, and stability in the face of climate change in future might be used as a measure of selectable features in environmentally induced adaptations (**Figure 1**). Plant stress driven changes can be either temporal or permanent and stable. These are carried to the next generations and make the plant adaptable to future higher levels of stresses [34].

Epigenetic changes can be observed in same species in different habitats and can provide raw materials for natural selection in climate change induced stresses. For example, changes in DNA methylation patterns were correlated to morphological modifications abundance of trichomes and spines in plants [35], modified leaf

#### **Figure 1.**

*The impact on the plant cells, genetic and epigenetic constitution by various intensity levels and durations of biotic and abiotic environmental stresses. The short-term effects are mainly for survival strategies while the long-term effects drive a plant into dimensions of adaptive speciation. Most epigenetic changes occur more in short durations and are highly reversible unlike long-term genetic and mutational changes. However, epigenetic changes can be assimilated into phenotypes in long-term evolutionally durations.*

palatability [10], and later long-term differential vegetation browsing was observed [36]. This is because environmental stresses have been known to alter growth and productivity of even agricultural crop plants [15]. These epigenetic variations occur rapidly and can be used to predict the long-term effect of similar environmental stresses or hazards including heavy metals, air pollution, electromagnetic radiations, and high temperatures.

Epigenetic changes can affect genetic processes including DNA replication, DNA repair, transcription, transposon stability, and even cell differentiation [37]. These predictions can be simulated and studied in controlled laboratory environments, for example, recent analysis of plant mutations showed that epigenomeassociated mutation bias could contribute to environmental effects on mutation [38, 39]. Studies in cosmopolitan plants can give an idea of the particular key mechanisms, which make them to survive and thrive in diverse environmental conditions. Species such as grasses can survive extreme temperature by shutting down entire metabolism and seem as if they are dead. They, however, rejuvenate rapidly at the onset of favorable conditions. The seeds of such plants can serve as study materials for such studies. They actually make all their processes to be in dormant state in adverse conditions.

Recent studies on plant microbiome show interactions that have symbiotic relationship, which reduce plant stress signaling [40]. Another epigenetic plant molecule of interest in abiotic stress that has been given recent attention is melatonin. The exogenous application of melatonin influences both physiological and molecular activities in a plant [41–44]. Furthermore, chitosan has been found to have multifaceted effects in various plant crops such as maize, sun flower, and potato in adjusting in abiotic stresses and improving on crop productivity. Studies in the correlations between epigenetics and biotic interactions also are addressing morphological plasticity to identify epigenome markers to improve crop productivity [45]. The molecular basis of such effects is still yet to be fully understood [46, 47], although recent bioengineering predicts possibilities of more precision genome editing using the CRISPRCas9 system application in the generation of alleles to improve plant yields under various abiotic stresses [2]. This is future, which was predicted by [48].

*Introductory Chapter: Inevitable Cytogenetic, Genetic, and Epigenetic Changes Contributing… DOI: http://dx.doi.org/10.5772/intechopen.102991*

## **Author details**

Josphert Ngui Kimatu Department of Life Sciences, School of Sciences and Computing, South Eastern Kenya University, Kitui, Kenya

\*Address all correspondence to: jkimatu@seku.ac.ke

© 2022 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.

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## **Chapter 2**

## Protein Metabolism in Plants to Survive against Abiotic Stress

*Bharti Thapa and Abhisek Shrestha*

## **Abstract**

Plants are frequently subjected to several abiotic environmental stresses under natural conditions causing profound impacts on agricultural yield and quality. Plants can themselves develop a wide variety of efficient mechanisms to respond environmental challenges. Tolerance and acclimation of plants are always related to significant changes in protein, cellular localization, posttranscription, and posttranslational modifications. Protein response pathways as well as pathways unique to a given stress condition shared by plants under different stressed environment are discussed in this chapter. The various signaling of protein such as fluctuation, overexpression, and silencing of the protein gene are observed to be modulated in drought-tolerant plants. Similarly, gene expression, RNA processing, and metabolic process take place to cope with drought conditions. For adaption in water-submerged conditions, plants undergo reactive oxygen species (ROS), cell wall modification, proteolysis, and post-recovery protein metabolism. Heat shock protein and protein and lipid contents vary and play pivotal role in resisting low and high temperatures. In a nutshell, this paper provides an overview of several modification, synthesis, degradation, and metabolism of protein in plants to cope with and revive again to normal growing conditions against abiotic stress, emphasizing drought, submerged, extreme cold, and heat temperatures.

**Keywords:** protein, abiotic stress, tolerance, acclimation, yield

## **1. Introduction**

Plants have developed a wide variety of highly sophisticated and efficient mechanisms to sense, respond, and acclimatize to a wide range of environmental changes. They have responded by activating tolerance mechanisms at multiple levels of organization (molecular, tissue, anatomical, and morphological), through the adjustment of membrane systems and cell wall architecture. This includes altering the cell cycle and rate of cell division and also by metabolic tuning [1]. Many molecular genes are induced and repressed by abiotic stresses at molecular level involving a precise regulation of extensive stress-gene networks [2, 3], and their products may function in stress response and tolerance at cellular level. Proteins involved in multiple protein functions, such as biosynthesis of osmoprotectant compounds, detoxification enzyme systems, proteases, transporters and chaperones, act as a first line of direct protection from stress. Moreover, regulatory proteins, for instance, transcription factors, protein phosphatases and kinases, and signaling molecules activation are essential in regulation of signal transduction and stress-responsive gene expression [4, 5].

Generally, observed tolerance responses toward abiotic stress in plants are composed of stress-specific response mechanisms and adaptive responses that confer strategic advantages in adverse conditions. In energy maintenance, general response mechanisms related to central pathway are involved, including calcium signal cascades [6], reactive oxygen species (ROS) signaling elements [7, 8], and energy deprivation signaling (energy sensor protein kinase, SnRK1) [9]; and induction of these central pathways is observed during plant acclimation toward different stress. Protein kinase SnRK1, despite being central metabolic regulator of the expression of genes related to energy-depleting conditions, also get activates when plants face different sorts of abiotic stresses such as drought, salt, flooding, or nutrient depravation [10, 11]. SnRk1 kinases alter over 1000 stress-responsive genes expression allowing the re-establishment of homeostasis by repressing energy consuming processes, thus promoting stress tolerance [10, 12]. Optimization of cellular energy resources during stress for plant acclimation has been found to be imperative; and partially arrested energetically expensive process, such as reproductive activities, translation, and some biosynthetic pathways [13]. For instance, in maize, during salt stress and potassium deficiency stress, nitrogen and carbon assimilations are impaired; also, the synthesis of free amino acids, chlorophyll, and protein is also affected [14, 15]. After cessation of energy-expensive process, energy resources can be redirected to activate protective mechanisms [16].

#### **1.1 Plant stress tolerance and resistance**

Plants are sessile organisms, which are continuously being confronted with several detrimental factors rising from ever-changing environment, and to cope with these problems, they have developed sophisticated and delicate defense mechanisms. In fact, diverse defense signal including the production of reactive oxygen species (ROS), change in redox potential or cellular level of Ca2+ ion, disruption of ion homeostasis, and membrane fluidity adjustments are activated [17, 18]. Once external stress is sensed via specific receptors, foreign signal is induced into intracellular downstream signaling pathways including the activation of protein kinase or phosphatase, stimulation of downstream target proteins, and biosynthesis of phytohormones for the control of plant growth/development [19, 20].

#### **1.2 Role of amino acid during stress**

Gene expression can be adversely affected by salinity, drought, and temperature stress, and many genes coding for enzymes involved in cellular metabolism are differentially expressed upon stress, thus modeling some stress-related transcription factors to induce changes in stress-associated metabolite levels [4].

For the synthesis of secondary metabolites and signaling molecules, several amino acids can act as precursors, for instance, polyamines are derived from Arg [21], Met synthesized the plant hormone ethylene [22], and conversion of Lys to N-hydroxy pipecoline is necessary for immune signaling [17, 23]. Moreover, several aromatic amino acids, such as Phe, Tyr, and Trp, or intermediates of their synthesis pathways produce a broad spectrum of secondary metabolites possessing multiple biological functions and health-promoting properties [24]. Usually, plants exposed to different abiotic stresses tend to accumulate free amino acids [25, 26], as exemplified to this response, [27] reported extensive accumulation of amino acid in response to drought stress in maize, cotton, tomato, and the resurrection plant. Also, recent studies conducted by [26, 28–30] suggest increment in free amino acids as a result of autophagy and abscisic acid. Similarly, plants surviving in stressed environment can use amino acids as an alternative for mitochondrial respiration

*Protein Metabolism in Plants to Survive against Abiotic Stress DOI: http://dx.doi.org/10.5772/intechopen.102995*

substrates during inadequate carbohydrate supply due to a decrease in photosynthesis rates [29, 31]. Although ambiguity still remains for the specific role of catabolic pathways, the degradation pathways for Lys and the branched-chain amino acids Val, Leu, and Ile have already been identified as crucial factors for dehydration tolerance for *Arabidopsis* [32]. And, soon after reviving of plants to favorable growth conditions, reprogramming their metabolism to switch back for survival and active growth is necessary.

Members of the AP2/EREBP (Apetala2/ethylene-responsive element binding protein) family of transcription factors, CBF/DREB1 proteins (C-repeat binding factor or dehydration responsive element binding proteins), such as CBF1/DREB1B, CBF2/DREB1C, and CBF3/DREB1A play an important role in the transcriptional response to osmotic stress [33–37] and stated improved tolerance of *Arabidopsis* to freezing, drought, and/or salt stress via overexpression of these transcription factors, and [38, 39] supported above researchers confronting plants overexpression of CBF/DREB1 accumulated higher levels of proline and soluble sugars (glucose, fructose, sucrose, and raffinose) when grown under normal growth conditions and during cold acclimation. Conclusion made from [39, 40] suggested overall metabolic profile of CBF3/DREB1A overexpressers grown at normal growth temperatures resembled that of cold-exposed plants.

#### **2. Proteomic overview on abiotic responses in plants**

The biological research of abiotic stress in plants can be studied in broad range of transcriptomic and proteomic-based, provides the comprehensive information, during and following stress condition, on alteration of gene expression and proteome profile, the study about 30 min to 1 day after induction, and time lapse between transcriptomic and proteomic suggest more than 50% of genes responsive to flood, heat, and other stress were found to encode transcription regulators [41].

#### **2.1 Protein metabolism in plant roots and shoots due to drought stress**

Prolonged water deficit in the soil causes drought, which vastly affects the metabolism and physiological function in growing plant especially roots and responsive for water supply from soils to leaves and photosynthesis, respectively. Most of the proteomic evidence has been noticed due to drought condition, six steps prominently occur in the responsive drought stress. Signaling and sensing receptor, yet not specially but drought-responsive photoreceptor, phytochrome C1, found in maize, phytochrome gene (i.e., *PHYA*, *PHYB*, and *PHYE*) in *Arabidopsis*, believed to regulated the transcription of light responsive genes by modulating the activity of several transcription factors and involved in suppressing drought tolerance. Other signaling cascades, G protein subunits (alpha and beta), small G protein (e.g., Rasrelated protein Rab7 and Ras-related nuclear protein Ran), and Ran-binding protein 1 (play important role in cell cycle and DNA synthesis) regulate positive role in drought stress [42], involved in vesicle trafficking, intercellular signaling, polar growth, plant hormone signal cross talk, and stress response [43]. The *PgRab7* gene was upregulated by dehydration in *Pennisetum glaucum* [44], while overexpression of the peanut *AhRabG3f* exhibited an enhanced tolerance to drought stress in transgenic peanut (*Arachis hypogaea* L.) [45] but negative role in Arabidopsis. Calciumbinding proteins (CaBs), such as calmodulin (CaM), calcium-sensing receptor (CaSR), calreticulin (CRT), and calcium-dependent protein kinase (CDPK), enhanced the survival of *Triticum aestivum* [46], and several protein kinases (e.g., serine/threonine-protein kinase, germinal center kinase (GCK)-like kinase

MIK, receptor-like protein kinase HERK 1-like, phototropin family protein kinase, and salt-inducible protein kinase), imply their role in drought response signaling pathway, in addition to phosphorylation level of protein phosphate 2C (PP2C), acts as negative regulator for plant drought tolerance in the abscisic acid (ABA) signaling pathway, which can inhibit the activity of SnRK, leading to a decrease of the phosphorylation of its substrates in the signaling cascade [47]. Similarly, 14-3-3 protein availability fluctuation shows the drought condition and reported that drought stress can directly alter the abundance of 14-3-3 proteins [48]. In addition, overexpression or silencing of the 14-3-3 protein genes can modulate drought tolerance of transgenic plants (e.g., *Gossypium hirsutum* and *Arabidopsis*) [49, 50].

Phytohormones play important role in signal transduction pathways such as drought-increased ethylene-responsive transcription factor (ERF) in *Gossypium herbaceum* [2] (and some members of drought-responsive auxin-binding protein (ABP) family in *Quercus robur* [51] *Zea mays* (41) and polar clones [52]. Under drought stress, *ERF* gene was induced in *G. herbaceum* [53, 54], and its overexpression in various plants, such as sugarcane *SodERF3* overexpression in tobacco, tomato *TERF1* in rice, and *Brassica rapa BrERF4* in *Arabidopsis*, can improve plant drought tolerance. *BpERF11* was found to negatively regulate osmotic tolerance in *Betula platyphylla* [42] ABP members (i.e., ABP2, ABP20, and ABP19a) are in response to drought stress, additionally TRIP-1 was phosphorylated by the brassinosteroid (BR)-insensitive I (BRI-1) protein, drought-increased TGF-β-receptor interacting protein 1 (TRIP1) was found in *Sporobolus stapfianus* and triggered the BR signaling pathways in water deficit condition.

Gene expression plays important role in the transcriptional regulatory networks, requires chromatin structure modification, i.e., histone, major protein of chromatin, and regulates the expression and high mobility group protein (HMG), involved in cell cycle progression. Among several histones, histone H1 was decreased in a drought-sensitive *Z. mays* cultivar, but increased in a drought-tolerant one [55], and H2B histone H1 was decreased in a drought-sensitive *Z. mays* cultivar, but increased in a drought-tolerant one [55]. Similarly, the phosphorylation level of HMG was significantly decreased in a drought-tolerant wheat cultivar, but increased in a drought-sensitive one [42] that reduced its binding to DNA, inhibiting replication and transcription.

Several RNA processing-related proteins changed over the stress condition, represent the critical for plants to cope with. Five glycine-rich RNA-binding proteins (GR-RBPs) increased with drought and three GR-RBPs decreased with drought, which bind to RNA molecules for transcriptional gene regulation and suspected to function in the regulation of specific gene expression. For instances, transgenic rice consists of GR-RBPs gene showing higher yield and drought recovery rate as compared with wild rice [56], besides overexpressed in *Camelina sativa,* reduced the drought tolerant. Similarly, S-like ribonucleases (RNases) specialized function as stress regulation, defense against microorganisms, phosphate scavenging, and even nitrogen storage, increased in rice under drought [57]. Additionally, an intron splicing-related protein, and maturase K (MatK) and multiple organelle RNA editing factor 9, involved in RNA editing in mitochondria and plastids, was found fluctuated in *Brassica napus* with the extension of drought stress [58] indicating the transcriptional regulation.

Most fundamental metabolic process to cope with drought stress, a plant can attribute to protein synthesis and turnover. Several proteins are involved in protein biosynthesis, such as ribosomal protein (RP), elongation factor (EF), translation initiation factor (TIF), tRNA synthase (TRS), and ribosome recycling factor (RRF), beneficial to protein synthesis, besides protein folding and processing varies cultivars and species. Instances, peptidyl-prolyl *cis*-*trans* isomerases (PPIases)

#### *Protein Metabolism in Plants to Survive against Abiotic Stress DOI: http://dx.doi.org/10.5772/intechopen.102995*

were significantly increased in *Oryza sativa* [6] and *Q. robur* [51], but decreased in a drought-sensitive cultivar of *Phaseolus vulgaris* [59]. Protein disulfide isomerases (PDIs) were increased in barley and *B. napus*, but decreased in *Agrostis stolonifera*, *Q. robur*, and poplar. Additionally, ER-luminal binding protein (BiP), trigger factor-like protein (TIG), most heat shock proteins (HSPs), and other molecular chaperones (i.e., calnexin, endoplasmin) were increased, but T-complex protein and HSP70-HSP90 organizing protein were decreased in drought-treated leaves. This protein helps in maintaining the normal protein folding, repairing, and renaturation of the stress-damaged protein, whereas HSP must popular function in protein folding in Arabidopsis and yeast to improve the drought tolerance.

Protein degradation, process of removing the abnormal, damaged protein, and maintenance of certain level of regulatory proteins during drought, includes the components such as ubiquitin/26S proteasomes, small ubiquitin-like modifier (E3 SUMO) ligase, and proteases/peptidases (ATP-dependent Clp proteas, cysteine proteinase, zinc metalloprotease, aspartic proteinase, serine carboxypeptidase, and aminopeptidases (APs)). These components show positive response in *P. vulgaris* [59] *Hordeum vulgare* [60], *B. napus* [58], and *Medicago sativa* [61] under drought condition, involved in ubiquitination, exhibited significantly increased values in drought tolerant and decreased in drought-sensitive leaves.

Due to drought condition, it interrupts the normal cellular mechanism, results to produce the ROS. Plants evolve diverse mechanism to keep ROS homeostasis in cells, including antioxidative enzymes, e.g., SOD (first defense mechanism by converting O2 into H2O2) and CAT (convert H2O2 into H2O and O2) and chemical antioxidant (e.g., glutathione and ascorbate). Diverse abundance of SODs in cystolic, peroxisomeas as well as in chloroplast helps in the drought tolerance and avoidance. For instance, increment of cystolic Cu-Zn SODs drought avoidance CT9993 and drought tolerance IR62266), while e chloroplast Cu-Zn SODs were increased in CT9993, but decreased in IR62266 [57], additionally in cultivar of *Malus domestica*, Cu-Zn SOD decreased and Fe SOD increased [54]. Similarly, in Ascorbate-Glutathione (AsA-GSH) pathways, the ascorbate peroxidase (APX) reduces H2O2 to H2O using ascorbate (AsA) as an electron donor, then the oxidized AsA is restored by monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) [62]. GR catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form GSH and work out for the drought tolerance. In addition, some proteins that involved in glutathione-mediated ROS scavenging: glyoxalse (GLO), phospholipid hydroperoxide glutathione peroxidase, glutamate-cysteine ligase (GCL), glutaredoxin (Grx), and monothiol. GLo catalyzes the detoxification of methylglyoxyl, whereas GCL, first enzymes in GSH biosynthesis pathways found in drought stressed *B. napus* [58]*.* Additionally, Prx/Trx also catalyzes the reduction of H2O2, whose abundance response to drought. Trx-linked enzyme, methionine sulfoxide reductase (MSR), involved in conversion of methionine sulfoxide to methionine, protects cells and tissues from H2O2-induced stress. Besides, Glutathione Peroxidase/Glutathione S-Transferase pathways, GPX catalyzes the reduction of H2O2 using Trx [63], and GST catalyzes conjugation reactions between GSH and a number of xenobiotics, playing a crucial role in the degradation of toxic substances. To cope with drought, GPXs found increased in *Boea hygrometrica* [64], *E. elongatum* [65], and *B. napus* [58].

There will be occurrence of pathogen when left plant for water deficit condition, but some pathogenesis-related protein, namely chitinase, disease resistance protein (DRP), polyphenol oxidase (PPO), oryzacystain, pathogen defense-related protein 10 (PR10), and disease resistance gene analog PIC15 increased in the response of drought condition. These proteins act as the pathogen by acting on insect exoskeleton and fungi cell walls, catalyzing the oxygen-dependent oxidation of

phenols to quinines' during plant defense, acting as cysteine proteinase inhibitor in the phytocystatin family of proteinase inhibitors. For example, overexpression of oryzacystain gene in Tobacco displayed an increase of drought tolerance by improving total SOD and guaiacol POD activities.

Osmotic regulation will be hindered due to exposed to water deficit, but important osmotic homeostasis-related protein, namely embryogenesis abundant (LEA) protein, dehydrin (DHN), and betaine aldehyde dehydrogenase (BADH), which function as cellular protectants to stabilize cellular components, protein structure through detergents and chaperone like properties, act as calcium buffer. LEA proteins were also increased in *Z. mays* [55] and *B. napus* [58] under certain drought conditions.

Cell division and cell wall formation decreased due to decrease of phosphorylation of several protein (cell division cycle protein, division protein ftsZ1, and cyclin A2) when exposed to drought, which implies the suppression of cell growth. Cytoskeleton and cell wall component require for cell division, morphogenesis, and signal transduction, while cytoskeleton protein, namely actin, kinesin motor protein, tubulin, profilin, actin depolymerizing factor, and fibrillin to check the cell growth during stress. Additionally, the translationally controlled tumor protein homolog (TCTP) is a Ca2+-binding protein, which protect against stress and apotosis, cell growth, and microtubule organization, which was significantly drought increased in *H. vulgare* [60], *T. aestivum* [66], and *B. napus* [58], which would facilitate plant adaptation to drought stress.

Cell wall extensibility was directly affected by water loss, while cell wall polysaccharide synthesis/hydrolysis, lignin biosynthesis, and cell wall loosening in leaves were drought-responsive enzymes. Two enzymes, glycosylated polypeptide and pectinacetylesterase, involved for polysaccharides synthesis, another two enzymes xylanase inhibitor and polygalacturonase inhibitor, involved in polysaccharide hydrolysis inhibition. Three lignin biosynthesis-related proteins, phenylalanine ammonia-lyase (PAL), caffeic acid 3-*O*-methyltransferase, and caffeoyl-CoA *O*-methyl-transferase, catalyze the transformation of phenylalanine to cinnamylate of lignin biosynthesis, while two drought-increased cell wall structural proteins (i.e., glycine-rich protein and fasciclin-like arabinogalactan protein) enhance cell wall synthesis in response to drought by providing the UDP-glucose directly to the cellulose synthases and/or callose synthases [67], hence, improve the mechanical strength for minimizing water loss and cell dehydration. Another important activity of cell wall loosening/expansion, important aspect in the adaption to drought, which was related enzymes, polygalacturonase/pectin depolymerase (PG) in *O. sativa* [6] and xyloglucan endotransglycosylase (XTH), where PG degrade pectin, while XTH can cleave and reform the bonds between xyloglucan chains to regulate cell wall rigidity.

Membrane trafficking localized in mitochondrion, plasma, and vacuole. Two mitochondrion protein carriers (dicarboxylate/tricarboxylate carrier (DTC) and 2-oxoglutarate/malate carrier protein (OMC)), catalyze the transport of various metabolites (e.g., dicarboxylates, tricarboxylates, amino acids, and keto acids), play important role in gluconeogenesis, nitrogen metabolism, as well as biotic stress [68]. Another, Remorin, aquaporin and PEG, plant-specific plasma membrane protein have importance in plant-microbe interaction and signal transduction [69]. In addition, vacuolar H<sup>+</sup> -pyrophosphatase (V-PPase), vacuolar-ATPase (V-ATPase), and ABC transporter ATPase, important for or translocating H+ into the vacuoles to generate a gradient of H<sup>+</sup> , which provide a driving force for the accumulation of ions and other solutes in the vacuole and function for abiotic stress.

Photosynthesis inhibition is the primary detrimental effect due to drought stress, and related protein decrease. To cope with this situation, drought increased

#### *Protein Metabolism in Plants to Survive against Abiotic Stress DOI: http://dx.doi.org/10.5772/intechopen.102995*

protein involved in the photoreaction and Calvin cycle in leaves. Light-harvesting chlorophyll a/b-binding proteins (LHCB), involved in ABA signaling partially by modulating ROS homeostasis, besides, abundance of sedoheptulose-1,7-bisphosphatase (SBPase) and carbonic anhydrase (CA), catalyzes the reversible hydration of CO2, and influence in internal conductance and abundance of protein involved in photorespiration, significantly increases and decreases glycolate oxidase, glycine dehydrogenase, serine glyoxylate aminotransferase, and serine transhydroxymethyl transferase, aminomethyl transferase (AMT), and glycine dehydrogenase to adapt the drought stress. The mechanism in photorespiration can protect the photosynthesis from photoinhibition and prevent ROS accumulation in green tissues.

Involvement in carbohydrate and energy metabolism is important step to cope with drought condition. Phosphoglucomutases (PGluMs), fructose-bisphosphate aldolase (FBPA) in glycolysis and aconitate hydratases in TCA cycle increased in drought condition, which inhibit the accumulation of sugars as osmolyte or energy source for recovery, while the increase of glycolysis and TCA may act as a strategy for providing energy during the activation of stress defenses, especially when the photosynthesis was inhibited. The change in mitochondrial electron transport chain and ATP synthesis related protein implies ability to enhance energy production to maintain physiological activity and inhibit stress damage.

Due to the drought condition, nitrogen assimilation decreased in the reduction of NR, GS, and GOGAT, which was main reason for yield reduction. Similarly, the decline of aspartate aminotransferase (AST) and alanine aminotransferase (ALAT) indicates that drought stress inhibits the amino-acid metabolism and synthesis of other metabolites. At the same time, *S*-adenosyl-l-methionine (SAM) cycle was generally increased in leaves, including drought-increased. 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase (MetE), *S*-adenosyl-lhomocysteine hydrolase (SAHase), *S*-adenosylmethionine synthase (SAMS), and methionine synthase (MS), which implies that it enhances the methionine and osmo-regulant metabolism for plants to cope with drought stress.

Acetyl-coenzyme A carboxylase carboxyl transferase, acyl carrier protein, enoyl-acyl carrier protein reductase, and lipoxygenase 6 involved in fatty acid biosynthesis, and enzymes thiolase I, thiolase II, and acyl-CoA dehydrogenase used for fatty acid degradation. Greater composition of unsaturated fatty acid in membrane lipids contribute to superior leaf dehydration tolerance and maintain membrane integrity and preserve cell compartmentation under water stress, in addition, two flavonoid biosynthesis related proteins (i.e., chalcone isomerase (CHI) and dihydroflavonol-4-reductase) involved in secondary metabolism were also changed in response to drought.

#### **2.2 Protein metabolism under flooding and submerged stress condition**

Deprivation of the soil oxygen due to consequence of flooding and forced the plant to shift from aerobic to anerobic respiration [70], which regenerate NAD<sup>+</sup> , through ethanol fermentation by selectively synthesizing flooding-inducible proteins involved in sucrose breakdown, glycolysis, and fermentation [13]. Several glycolysis-related proteins, including fructose-bisphosphate aldolase, phosphoglycerate kinase [64], glyceraldehyde-3-phosphate dehydrogenase [71], enolase [72], sugar isomerase, phosphofructo-kinase [73], and pyruvate kinase [72] are increased in soybean under flooding stress, indicate the glycolysis and fermentation pathways activation, initiating for plants protecting plant from flooding induced damage, whereas decrease of fructose-1,6-bisphosphate aldolase and sucrose-fructan 6-fructosyl transferase in wheat show response to flooding stress. Othersides, fermentation under anaerobic condition, influence the accumulation of fermented related

proteins such as alcohol dehydrogenase (ADH) and pyruvate carboxylase, and indicates that activation of the alcohol fermentation pathways, to cope the hypoxic condition. The conversion of acetaldehyde to ethanol by ADH with concurrent reoxidation of NAD<sup>+</sup> for the continuation of glycolysis. The fermentation related enzyme pyruvate decarboxylase, and aldehyde dehydrogenase increase to accelerate the energy production via nonoxidative pathways, even growth is suppressed.

In other sides, flooding stress induces impairment of the electron transport chain in plants. Protein related to complexes II, IV, and V of the electron transport chain decreased in abundance and while, succinate-semialdehyde dehydrogenase, 2-oxoglutarate dehydrogenase, and gamma-amino butyrate are significantly increased, which are required for energy production via non-oxidative pathways [72]. Oxaloacetate produced in TCA cycle stimulates phosphoenol pyruvate synthesis and provides the indirect simulation for the continuation of glycolysis. Reduction of energy metabolism-related proteins, including citrate synthase, glutamate dehydrogenase, and adenosine kinase, in wheat roots under waterlogging stress [74]. In addition, energy-related proteins such as beta-amylase, malate dehydrogenase, fructose-1,6-bisphosphatase, and phosphoenol pyruvate carboxykinase are decreased in response to flooding stress, indicating that gluconeogenesis is suppressed in wheat under these conditions [10]. RuBisCo sub unit binding protein alpha sub unit and RuBisCO activate degraded and senescence in high ROS condition and decreased the chlorophyll content, results to decrease in net energy production.

ROS recognized as toxic byproduct of aerobic metabolism and controlled by anti-oxidants and anti-oxidative enzymes. The plant development of wellorganized scavenging mechanism to overcome ROS toxicity likely to led to the use of reactive molecules as signal transducers in plant cells. ROS production in cellular organelles, such as plastids, mitochondria, and peroxisomes, involved in signaling cascades controlled by production and scavenging of ROS intermediates [27]. ROS scavengers, such as peroxidase, APX, cytosolic APX, and superoxide dismutase (SOD), linked to bio photon emissions and decreased photosynthesis and beneficial for normal metabolism and cell signaling.

Cell wall modification related proteins, namely polygalactouronase inhibitorlike and expansion-like B1-like proteins and cell wall synthesis related protein such as cinnamyl-alcohol dehydrogenase and cellulose synthase-interactive protein-like protein abundance response under water logged condition. Flooding stress induces the assimilation of methionine and promotes cell wall hydrolysis, thereby restricting growth so, under the waterlogged stress, cell wall synthesis related proteins decrease, cell wall loosening related protein increase and cell wall lignification is suppressed.

Proteolysis, protein folding and storage plays important role in the removing the flooding damage induced non-active proteins [40]. Heat shock proteins act as molecular chaperones in preventing protein aggregation, translocation of nascent chains across membranes, assembly or disassembly of multimeric protein complexes, and targeting proteins for lysosomal or proteasomal degradation [40]. The ubiquitin/proteasome-mediated proteolysis of enzymes involved in glycolysis and fermentation pathways may be negatively controlled under the hypoxic condition caused by flooding stress [40].

Post recovery protein metabolism is less studied but studied by [75] Gro-EL-like chaperone ATPase, 26 S proteasome regulatory subunit 7, 26 S regulatory subunit S 10B, and cyclophilin were decreased in seedlings recovering from flooding stress, whereas globulin-like protein, Kunitz trypsin protease inhibitor, and peptidylprolyl cis-trans isomerase 1 were increased, and soybean root recovers from flooding by altering cell structure, strengthening cell wall lignification, and scavenging toxic ROS.

## **2.3 Cold stress**

One of the major abiotic stresses is cold or low temperatures (LTs) that severely affect plant growth and survival. Chilling or freezing with temperatures <20°C and < 0°C respectively can induce ice formation in plant tissues which causes cellular dehydration [39]. To be able to withstand in this adverse condition, plants adopt several strategies, such as production of more energy via activation of primary metabolisms, leveling up of antioxidants content and chaperones, and maintenance of osmotic balance by altering membrane structure [76].

## *2.3.1 Protein metabolism in cold stress*

Several articles and reviews deals with the metabolic responses of plants at low temperature, where some attempted correlating metabolic and biochemical responses with cold tolerance. Solaw [77] noted correlative studies of biochemical changes does not enable understanding of cold acclimation (CA) leading to increased freezing tolerance and till date no any new approaches in molecular biology and genetics have been extensively enlisted on study of cold-tolerance and injury mechanisms. However, few studies of CA started focusing on some of the more rapid plant physiological and molecular responses subjected to LTs, which revealed that within the hours of LT exposure, plant and algal cells can rapidly initiate to alter membrane lipid composition [78], RNA [79], and protein content. These findings of rapid biochemical alterations in response to L T convince the rapid induction of freezing tolerance at inductive temperatures and by desiccation and ABA at non inductive temperatures [80] and ABA [10]. This suggests a possible molecular basis, at minimum, for the adjustment of metabolism to low nonfreezing temperature, and perhaps for freezing tolerance. Also, upon exposure to LT, it consists of repeated observations that a number of enzymes show shifts in isozymic composition, whereas both quantitative and qualitative differences in the protein content is shown by numerous electrophoretic studies between non-acclimated and cold acclimated tissues.

## *2.3.2 Enzyme variation*

Compared with plants maintained at warm temperature, [20] reported changes in activity, freeze stability, and isozymic variation in plants subjected to LTs. He mentioned increased peroxidase activity in hardened stems of four widely unrelated woody species when electrophoretic techniques to separate enzymes from non-hardened and hardened tissues. Here, peroxidase isozymes present in hardened tissues were not found in other three non-hardened tissues. Similarly, during deacclimation, no change in peroxidases, glucose-6-phosphate, 6-phosphogluconate, and malate dehydrogenases was observed in willow stem [81], however, differences were observed in lactate dehydrogenase where the activity increased during deacclimation. Similarity as above findings was illustrated by [82] in which invertase enzyme in wheat leaves undergoes a shift from a lower-molecular weight form to a higher-molecular-weight form at LT. Different kinetic properties is exhibited in larger form functionally replacing small form in cold-hardened plants [83]. Also, Krasnuk and colleagues [6, 84] observed increased activity of a number of dehydrogenases associated with respiratory pathways, including glucose-6-phosphate dehydrogenase, lactate, and isocitrate dehydrogenase [6] during a comprehensive studies with alfalfa. Thus [85] suggests higher amounts of enzyme may increase in activity and soluble protein content indicating increased soluble protein content and enzyme activity could be part of the adjustment of metabolism to the kinetic constraints imposed by LTs.

A more recent study of glutathione reductase from spinach carried out by [26] demonstrated not only additional isozymic forms in cold-acclimated tissue but also increased activity, freezing stability, and altered kinetic behavior and the activity of this particular enzyme was decreased by freezing/thawing both in vitro and in vivo. However, the enzyme found in cold-acclimated plants was less sensitive than its counterpart from non-acclimated plants to freezing from nonacclimated plants. In contrary, kinetic parameters and freeze/thaw inactivation was observed identical in ferredoxin NADP reductase from nonacclimated and cold-acclimated wheat [86], whereas activity was increased during CA. Therefore, [85] illustrated the potential for alterations in enzymes in response to low temperature exposure and the apparent selective basis where such changes can occur.

Ribulose bisphosphate or oxygenase from winter rye is the best-characterized enzyme relative to non-acclimated and cold-acclimated plants. Early in vitro studies studied by [87] noted purified enzyme from both non- and cold-acclimated plants demonstrated an increased stability of catalytic activity to denaturants and storage at −25°C of the enzyme from cold-acclimated plants. Moreover, [87] presented evidence of a stability in vivo conformational change during low-temperature adaptation that was not altered by purification of the enzyme. Also, osmotic concentration of the purified enzyme caused a greater degree of aggregation through intermolecular disulfide bond formation of the large subunit from non-acclimated plants [4] also claimed, similar to rye, the enzyme purified from freezing sensitive and -tolerant potato species demonstrated structural differences that paralleled variation in freezing tolerance much in the same way. However, the study still remains in ambiguity for the stable change in conformation, kinetic properties, and differential cryostabilities of this enzyme from cold-acclimated leaves or cold tolerant potato species. Given that a single chloroplastic gene encodes for large subunit and not possess even a minute chance for the synthesis of an alternative cryostable large subunit from another gene. Also, in many plants, always, a small gene family codes the small subunit, a change in the small subunit may possess subtle effect on the cryostability and other properties of the holoenzyme. Equally possibility occurs in LT -specific posttranslational processing, although there is no evidence to support this concept. In addition to isozymic and conformational differences of enzymes in response to L T exposure, Griffith, stated supramolecular interactions can also be affected.

#### *2.3.3 Protein content*

According to [88], accumulation of soluble protein in cold-acclimated cortical bark cells of black locust trees was first correlated with freezing tolerance about 40 years ago. These study may not be explained as simply as stated in past, [88] suggests there are many reasons why some plants might accumulate soluble proteins during CA; but with the exception of a protoplasmic augmentation hypothesis without clear mechanistic rationale for conferring greater freezing tolerance for this hardening response. In temperate deciduous perennials like black locust could provide the nitrogen source for the accumulation of proteins in the cortical cells of the living bark, in expense of nitrogenous materials during senescence. Parsell and Lindquist [89] supports a possible functional role of the increased soluble protein in cold tolerance was the fact that an evergreen, red pine, also accumulated soluble proteins during the winter, similarly, cortical bark cells need not to act as vegetative storage in evergreens nevertheless, it cannot be refused that one or more minor components of the total protein content could function in freezing-tolerance mechanisms.

Most of the studies have confirmed the presence of new protein species in cold-acclimated and freezing-tolerant plants. When these plants are compared to non-acclimated plants, subtle shift in protein content in cold-acclimated tissues involving mostly the appearance and disappearance of minor bands in gel can be observed [85]. Existing evidence at present includes several studies of purified plasma membranes from non-acclimated and cold-acclimated tissue. Tzin and Galili [90] emphasized on declination of more than 20 proteins in cold-acclimated leaf plasma membranes, whereas 11 had increased their concentration, while 26 proteins were new and unique to membranes from hardened tissue, yet increased levels of high-molecular-weight glycoproteins were other alterations included during CA.

## **2.4 Heat stress**

Some defense mechanisms can be triggered in response to several stresses, such as expression of obvious genes which were not expressed under normal situations, resulting increased synthesis of protein groups [60]. These groups in cases of heat are called as Heat Shock Proteins (HSPs), "Stress-induced proteins" or "Stress proteins" [49].

According to [14] declination in normal protein synthesis occurs when exposed to high temperatures, thereby increasing selective translation of mRNAs for characteristic sets of HSPs. Heat responding phenomena in plants generally observed with concomitant reduction in protein synthesis of new or constitutive HSPs. Jin et al. [35] observed reduction in total protein synthesis at of 40°C and above in soybean. The HSPs, in plants, consists an abundant group of low mo1 wt polypeptides with higher molecular weight families [91], where some of them found to function as chaperones minimizing high-temperature stress damage partially denaturing proteins and preventing breakdown or aggregation. Response toward heat includes increase in binding of ubiquitin to conglomerated high molecular weight protein [11] which both increase and decrease ubiquitin transcripts expression [17].

## *2.4.1 Role of heat shock proteins*

Levitt et al. [92] reported formation and folding patterns of any protein in three dimensional structure determines their function and [93] favored above statement and confronted with the findings illustrating 50% of principle amino acids sequence is necessary for formation of three dimensional structure which signifies the importance of HSPs in folding of other proteins. As plants were induced in heat stress, HSPs protects cells from injury and facilitates their recovery and survival to normal growth conditions [49]. Also, [94] specified the role of HSps as molecular chaperones during heat stressed condition, apart from ensuring maintenance of correct protein structure, which is basically different than in non-thermal stress where proteins unfolding is not the primary effect and protection could occur in any ways.

Seo et al. [95] also focused the general role of HSPs as molecular chaperones, regulating folding and accumulation of proteins as well as localization and degradation in all plant and animal species, thus preventing the irreversible aggregation of other proteins and participate in refolding proteins during heat stress conditions [96].

Different HSPs with their unique role are described below:

## *2.4.1.1 Small heat shock proteins (sHSPs)*

These contains a common alpha-crystallin domain containing 80–100 amino acid residues contained in the C-terminal region [97]. The characteristics features of this proteins is degradation of protein having unsuitable folding [11]. Another attributes

that make it indifferent from other class is independency of its activity from ATP [98]. A recent review from [99] concluded the presence of some indications that sHSPs play crucial role in membrane quality control, thereby potentially contributing the maintenance of membrane integrity under stress conditions.

## *2.4.1.2 HSP60*

This class, called as chaperonins, is known to be important in assisting plastid proteins such as Rubisco [100]. Some studies like [101] pointed out that they might participate in folding and aggregation of proteins that were transported to chloroplasts and mitochondria. These proteins are different from other proteins, after transcription and before folding, to prevent their aggregation [42].

## *2.4.1.3 HSP70*

These HSP70 functions as chaperones, in almost all organisms, for newly formed proteins to check their accumulations as aggregates and folds in a proper

#### *Protein Metabolism in Plants to Survive against Abiotic Stress DOI: http://dx.doi.org/10.5772/intechopen.102995*

way during their transfer to final location [102]. Furthermore, cooperation in the activity of HSp70 and sHSPs primarily function as molecular chaperone and play an important role in protecting plant cell from detrimental effects of heat stress [83] stressed on crucial role played by HSp70 and sHSP17.6 in the development of cross adaptation to temperature stress in grape vines induced by heat acclimation (HA) and cold acclimation (CA).

## *2.4.1.4 HSP90*

The protein from HSP90 class shares the role in many chaperone complexes and has important role in signaling protein function and trafficking [89]. Furthermore, other important attributes retained by these class includes regulation of cellular signals, such as the regulation of glucocorticoid receptor (GR) activity [103].

## *2.4.1.5 HSP100*

What makes it unique from other class is the reactivation of aggregated proteins [42] by re-solubilizing nonfunctional protein aggregates and also by degrading irreversibly damaged polypeptides [104, 105]. Members of this class are not restricted only to acclimation to high temperatures but also housekeeping functions necessary in chloroplast development are also provided by specific member (**Figures 1** and **2**) [106].

**Figure 2.** *Transcription [100].*

## **3. Conclusion and future prospective**

Abiotic stresses are major limiting factors for plant growth and yields and with various acclimation responses at morphological, physiological, metabolic, and molecular level coordinated by complicated regulatory networks comprising genes, phytohormones, ROS, and other signaling components. The abundance of ion channels protein and trans-membrane water found indicated the change in ions/ osmotic balances, but the phenomenon was not observed in flooding conditions. In addition, the preventive measure against the oxidative damage caused due to ROS levels under abiotic stress, higher abundance of ROS scavengers plays a great role in this matter, whereas the abundance of ROS scavengers was low in the flooding condition. On the other hand, protein folding due to molecular chaperone and disease, defense-related proteins such as proteolytic enzymes and proteosomal factors under stress, indicating the refolding of denatured proteins and proteolytic elimination of damaged proteins. This review paper showed the different protein metabolism occurs during the metabolic stages, and secondary metabolism-associated proteins escape and tolerate mechanism under different abiotic stress.

At the recovery stages, increased lignin biosynthesis results in enhanced mechanical strength by hardening of cell wall. Changes in abundance for cyto-skeletons associated proteins can be overlooked upon compensation against the reduced cell size as well as repairing injuries caused by drought and flood stress. Moreover, the levels of proteins related to *de novo* proteins synthesis*, growth-related* signaling and secondary metabolism are enhanced during flood replenishment of the stress induced effects. These stress-induced effects can be recovered by compensatory mechanism.

Only after proteomic studies could make us aware about the mechanism involved in abiotic stress condition. Analyzing of the plant response and abundance of protein and stress tolerant crops will lead to better understanding of the mechanism of plant to overcome the stress and recover. Moreover, some proteins showed the dynamic changes depending on plant species and stress intensity, which gives a clear interpretation of the mechanism in stress response. The integration of those finding from physiological, gene expression, and other large scale "omics" will help us to establish molecular networks of stress response and tolerance.

*Protein Metabolism in Plants to Survive against Abiotic Stress DOI: http://dx.doi.org/10.5772/intechopen.102995*

## **Author details**

Bharti Thapa1 and Abhisek Shrestha<sup>2</sup> \*

1 Centre for Biotechnology, AFU, Rampur, Chitwan, Nepal

2 National Sugarcane Research Program, NARC, Jitpur, Bara, Nepal

\*Address all correspondence to: shrestha.avi1425@gmail.com

© 2022 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.

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## **Chapter 3**
