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

to even plant death on being exposed to sever water scarcity (Ullah et al.,

2017).

Environmental stresses such as drought stress can trigger the accumula­

tion of large array of protective metabolites (Krasensky & Jonak, 2012).

According to Patel et al. (2020), the survival ability of plants in the presence

of drought stress mostly depends on the appropriate level of primary and

secondary metabolites in plants. Analysis of these metabolites can present

the key difference between drought tolerant and drought susceptible plant

species which can further be utilized for enhancing the tolerance capability of

plants (Llanes et al., 2018). Non-targeted or targeted metabolome study can

be used to decipher the metabolic changes that occur in plants in response to

stressed environment. Non-targeted metabolomics study helps to understand

an overall change in the level of metabolites in plants, whereas targeted

metabolomics study detects, analyze, and estimate the level of any known

metabolites in plants (Roberts et al., 2012; Van Meulebroek et al., 2016).

Drought stress directly hampers the metabolism of plants, thus forcing the

plants to reprogram the biosynthesis and transport of primary and secondary

metabolites (Ma et al., 2020). Regulation of metabolism is the key step for

implicating safeguarding of cellular osmotic potential during drought stress.

According to Liu et al. (2014), alteration in molecular pathways, activation

of signaling network, transcription, metabolism, and regulatory response

improve the resistance of the plants against drought stress. Kim et al. (2010);

and Joshi et al. (2016) reported that transcription factors such as NAC, MYB,

AP2/ERF, AREB/ABF and bZIP regulate the stomatal movement along with

regulating the expression of drought-responsive genes which eventually

regulate the metabolic pathways in plants. Thus, it can be mentioned that

drought tolerance in plants is a multi-genic trait. Various metabolomics

studies have shown the involvement of several metabolites in inducing

drought stress tolerance in several plants. On analyzing the leaves of drought

stressed Avena sativa via GC, Sanchez-Martin et al. (2018) reported that the

level of mono-, di-, and triacylglycerol, free fatty acid, linoleic acid, and

palmitic acid was induced in drought tolerant cultivar (Patones) whereas

no significant change was noted in drought susceptible cultivar, i.e., Flega.

They further showed that upon targeted measurements, the level of jasmonic

and isoleucine-jasmonic acid was initially enhanced in the tolerant variety

as compared to that of the susceptible variety. Similar studied was also

performed by Wenzel et al. (2015); Lanzinger et al. (2015); and Hein et al.

(2016) in Hordeum vulgare where they showed that the level of metabolites

like mannitol, galactinol, raffinose, myoinositiol, putrescine, proline, isocitric