Abiotic stress responses are of the utmost importance for plants because they cannot survive unless they are able to cope with environmental changes, such as high and low temperatures, drought, flooding, salinity, freezing, change in pH, strong light, UV, and heavy metals. Plants respond to various stresses at different levels, including molecular and cellular levels, as well as by modifying their metabolomes. Hence, studies on plant responses to stresses can be conducted at any of these levels to provide an understanding of the mechanisms involved. The present chapter focuses on the metabolomic approach to understand the responses of plants to different abiotic stresses, which can then be utilized to evolve strategies to combat such stress. Osmoprotectant metabolites, such as proline, glycine betaine, and polyamines, as well as carbohydrates, play important roles in the protection of plants against osmotic disbalances due to abiotic stresses. In addition, oxidative stresses are also overcome by an array of antioxidants, such as phenols, ascorbate, carotenoids, and a-tocopherol, as well as antioxidative enzymes. Signaling cascades activated during abiotic stresses lead to overexpression of protein kinases and stress proteins, and also involve molecules such as jasmonic acid and salicylic acid. Protein kinases and protein phosphatases that are encoded by large gene families often act in tandem to perform the phosphorylation and dephosphorylation leading to their activation and inactivation involved in stress signaling in plants. Analysis of microRNAs and transcriptomes has provided sufficient understanding of the gene expression levels during periods of stress. Hence, taken together, all these results can be utilized for identifying genes and/or metabolites overexpressed in tolerant species during periods of stress, and can be utilized to achieve higher tolerance and survivability during stresses.
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