ABSTRACT
Being sessile, plants often encounter diverse environmental stresses including drought. Recently, drought stress received a lot of attention from scientists because of the significant yield loss in crops during the last few years. To improve drought tolerance in plants, the drought-tolerance mechanism should be understood. Phytohormones are the key regulator of various processes related to drought tolerance improvement. Among them, ABA is known to play a crucial role in responding to drought stress. Under drought conditions, ABA regulates stomatal conductance, root development, photosynthesis and other morpho-physiological and molecular processes. After ABA, JA is also involved in drought tolerance in various ways, including stomata closure, the scavenging of reactive oxygen species (ROS) and root development. Moreover, auxins, cytokinins, ethylene, gibberellins and brassinosteroids also take part in the regulation of drought tolerance. These phytohormones regulate protective responses of plants against both biotic and abiotic stresses by direct- or crosstalking with each other. In addition, a higher production of ROS compared to normal concentrations is deleterious to plant cells. However, enzymatic and non-enzymatic machinery work together to scavenge ROS and protect plants from being damaged. This chapter highlights the role of phytohormones and scavenging of ROS under drought conditions.
