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Advances in Metabolomics Research in Environmental Stress Response in Plants

growth was maintained in the tolerant variety due to higher accumulation

of sugars (sucrose, maltose, and xylose), amino acid (proline) and organic

acids (shikimate and gluconate), thus indicating the potential role of these

metabolites in abrogation of salt toxicity. Additionally, similar reports have

also been reported in other plant species such as maize, tomato, wheat, and

barley (Zörb et al., 2013; Rouphael et al., 2018; Borrelli et al., 2018).

14.5 METABOLOMICS IN ATTENUATING THE NEGATIVE IMPACT

OF EXTREME TEMPERATURE

Temperature is one the major factors that regulates the development of the

plants. According to Pyl et al. (2012), plants are continuously exposed to

changes in diurnal or seasonal temperature and thus they must continuously

regulate their metabolism and physiology to ameliorate the negative effects

of extreme (higher or lower) temperature. On being exposed to either heat or

cold stress, plants can experience a severe degree of cellular, physiological,

molecular, and metabolic dysfunction (Guy et al., 2008). Plants on being

exposed to short-term cold stress become tolerant to freezing temperature

via cold acclimation. Similarly, earlier exposure to short-term heat stress

also induces the tolerance capability of plants to higher temperature known

as acquired tolerance which requires extensive metabolic reprogramming

(Espinoza et al., 2010; Caldana et al., 2011).

Various metabolome studies have shown that plants adapt themselves

according to the changes occurring in the surrounding environment by

altering their metabolite profile. Dhatt et al. (2019) showed that heat stress

altered the expression of 19 metabolites out of 57 metabolites as detected

by GC-MS in rice seedlings. They further reported that the level of sugar

molecules (glucose, fructose, and sucrose), starch biosynthesis and tricar­

boxylic acid cycle (TCA) were all enhanced in heat-stressed rice plants

during the early phase of grain filling. Recently, Wang et al. (2020) using

GC-MS technique, showed that the level of soluble sugar was enhanced in

heat-shocked Arabidopsis thaliana, whereas the plants which were exposed

to prolonged warming showed higher content of sorbitol and reduced level

of fumaric acid, citric acid, and L-malic acid. Thus, they inferred that plants

respond to heat by enhancing transpiration, photosynthesis, and respiratory

electron transfer, whereas on being exposed to prolonged heat, plants gener­

ally lower stomatal conduction and TCA cycle and increase photosynthetic

electron transfer rate. Similarly, Ren et al. (2019) analyzed the leaves of

Populus tomentosa using GC-MS and reported that the level of proline,