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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

which in turn damages the lipid membrane and also causes DNA and protein

disintegration.

The plant enhances their survival ability against salt stress through various

strategies and approaches such as ion homeostasis and compartmentalization,

osmotic adaptation, transport of ions, upregulating the formation of poly­

amines and antioxidants (de Freitas et al., 2019). Plants adapt themselves by

enhancing the formation of protective metabolites which eventually detoxify

the cytotoxic metabolites. The study of the metabolome profile of plants

exposed to salt stress gives a comprehensive knowledge about the change

in the level of these metabolites contributing towards higher tolerance level

of plants. Plants respond to salinity stress by enhancing the level of certain

amino acid such as phenylalanine, methionine, ornithine, glutamate, dihy­

droxy isoleucine, L-methionine, L-homomethionine, 3-methoxytyramine,

tetra-homomethionine, 1-(3-aminopropyl)-4-aminobutanal, feruloylagma­

tine, and methionine derivatives, whereas the level of other amino acids

like glutamine, cysteine, tyrosine, D-alanyl-D-serine, D-alanyl-D-alanine,

L-alanyl-L-glutamate were reduced (Benjamin et al., 2019; Seo et al., 2018;

D’Amelia et al., 2018). According to Hildebrandt et al. (2015), the higher

level of glycine betaine, proline, and ethanolamine maintains the enzymatic

activity and protein structure and also acts as an osmoregulator in plants

subjected to severe salt toxicity. The other group of secondary metabolites

like flavonoids and phenolic compounds also take part in the amelioration of

negative effects of salt stress in plants. Benjamin et al. (2019) reported that

the level of flavonoids (dihydroquercetin, 4’-methoxyisoflavone, flavonol

3-O-galactoside, epicatechin-3-O-gallate, and sakuranin) was enhanced in

the roots of halophytes on being exposed to salt stress. Additionally, GC-MS

based metabolome profiling of salt-stressed rice seedlings showed hyperac­

cumulation of some major amino acids like valine, leucine, isoleucine, and

proline (Gayen et al., 2019). In another study, Gupta & De (2017) demon­

strated that the level of two signaling molecules, i.e., serotonin and gentisic

acid was enhanced in the seedlings of salt stressed-tolerant rice cultivars

(Nonabokra and Bhutnath) as compared to that of the sensitive varieties

(MTU, 7029 and Sujala), Thus, these two molecules are important biomarker

compounds in the tolerant varieties. Similarly, Chang et al. (2019) reported

that the level of mannitol and sucrose was enhanced, whereas the level of

shikimate and quinate was lowered in the salt-tolerant rice variety. GC-MS­

based approach was followed by Shelden et al. (2016) to demonstrate the

changes in the root metabolome profile of the salt-stressed tolerant barley

cultivar (Clipper) and susceptible variety (Sahara). They showed that the root