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

melibiose, and raffinose was induced during heat stress which eventually

enhanced glycolytic pathways along with significant increase in the level of

amino acids (valine, leucine, and arginine).

In addition to high temperature, temperature, lower than the optimum

level can also cause significant damage to the plants. Using HPLC and NMR,

Chen et al. (2020) reported that cold stress significantly altered the level

of metabolites in banana. They demonstrated that cold stress enhances the

level of proline, leucine, isoleucine, acetic acid, malic acid, linoleic acid, and

sucrose that contributed toward higher stress tolerance in plants. Similarly,

Jian et al. (2020) reported that 47 and 41 metabolites were significantly regu­

lated in the leaves of cold stressed winter and spring oilseed, respectively. Of

all the metabolites identified, 83 metabolites were directed toward primary

metabolism. Secondary metabolic pathways like flavonoid biosynthesis,

phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, and carot­

enoid biosynthesis also contributed toward stress tolerance in plants. Seeds

of the cold stressed rice plants on being analyzed via HPLC and LC-MS/

MS showed that the level of 35 metabolites out of 730 metabolites were

significantly altered that mostly participated in phenylpropanoid and amino

acid metabolism pathways (Yang et al., 2019). Additionally, the effects

of cold stress in the metabolome of other plant species such as Nicotiana

tabacum, Vitis amurensis, Vitis vinifera, Hordeum distichon and Triticum

aestivum have been reported which showed that plants significantly change

their metabolic pathway on being exposed to lower temperature (Xu et al.,

2020; Chai et al., 2019; Yang et al., 2020; Cheong et al., 2019).

14.6 HEAVY METAL INDUCED ALTERATION IN METABOLOME OF

PLANTS

During the past few decades, increased anthropogenic activities, modern

agricultural norms and rapid industrialization have drastically increased the

level of heavy metals in soil that causes toxicity to the plants (Miransari,

2011; Kavamura & Exposito, 2010). According to Jarup (2003), 53 elements

belonging to the d-block of the periodic table has been recognized as heavy

metals due to their density (> 5 g cm^–3). Of all the elements known, carbon

(C), oxygen (O), hydrogen (H), magnesium (Mg), sulfur (S), nitrogen (N),

calcium (Ca), phosphorus (P), and potassium (K) are regarded as macronu­

trients. Copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), molybdenum

(Mo), boron (B), nickel (Ni), cobalt (Co), and chlorine (Cl) are considered