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Metabolic regulation is the key mechanism implicated in plants maintaining cell osmotic potential under drought stress. Understanding drought stress tolerance in plants will have a significant impact on food security in the face of increasingly harsh climatic conditions. Plant primary and secondary metabolites and metabolic genes are key factors in drought tolerance through their involvement in diverse metabolic pathways. Physio-biochemical and molecular strategies involved in plant tolerance mechanisms could be exploited to increase plant survival under drought stress. This review summarizes the most updated findings on primary and secondary metabolites involved in drought stress. We also examine the application of useful metabolic genes and their molecular responses to drought tolerance in plants and discuss possible strategies to help plants to counteract unfavorable drought periods.

Nitric oxide (NO) and salicylic acid (SA) are important signaling molecules in plant system. In the present study both NO and SA showed a protective role against arsenite (As) stress in rice plants when supplied exogenously. The application of NO and SA alleviated the negative impact of As on plant growth. Nitric oxide supplementation to As treated plants greatly decreased arsenic (As) accumulation in the roots as well as shoots/roots translocation factor. Arsenite exposure in plants decreased the endogenous levels of NO and SA. Exogenous supplementation of SA not only enhanced endogenous level of SA but also the level of NO through enhanced nitrate reductase (NR) activity, whether As was present or not. Exogenously supplied NO decreased the NR activity and level of endogenous NO. Arsenic accumulation was positively correlated with the expression level of OsLsi1, a transporter responsible for As uptake. The endogenous level of NO and SA were positively correlated to each other either when As was present or not. This close relationship indicates that NO and SA work in harmony to modulate the signaling response in As stressed plants.

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