Nitric oxide in drought stress signalling and tolerance in plants

The limited availability of water for agricultural usage and recurrent droughts resulting from the changes in the climatic patterns has significantly affected agriculture worldwide. In the light of the current global scenario, understanding physiological and molecular mechanisms adapted by plants to combat water deficit becomes essential to minimize multibillion dollar losses to the industry. The knowledge acquired would be further employed to enhance the tolerance of the agricultural crops to drought by adopting gene-manipulating techniques. This present chapter highlights the physiological and molecular basis of plant adaptive response to drought regulated by the nitric oxide (NO). Being a bioactive molecule, NO is involved in many physiological processes in animals and has also been known as a mediator of biotic and abiotic stress responses in plants. In recent years, various enzymatic and non-enzymatic pathways for its synthesis have been elucidated. Several important advancements have been made to reveal the roles NO plays in plant growth and development, and the role of NO as a signal molecule in activating ROS scavenging enzymes under abiotic stresses including drought has been established. In this review, we discuss how NO aids to the regulation of the antioxidative systems, stomatal closure and adventitious root formation under drought conditions. Apart from direct regulatory role at the physiological level, NO also plays an important role in plant acclimation to water deficit by activating stress defence genes via post-translational modifications.