**4.1 Oxidative damage**

Drought stress triggers an array of biochemical mechanisms including fluidity of the plasma membranes, osmolytes production, lipid peroxidation, reactive oxygen species (ROS) generation, rigidity of the cellular membranes and activation of different enzymes which are involved in oxidative defense system [50, 51]. Previously, in various crop species ROS generation instigates significant damage to cellular components and also causing damages to lipid peroxidation, proteins [52]. The drought stress induced ROS generation had calamitous effects on lipid membrane and protein. Among all the ROS superoxide radical (O2•−), hydrogen peroxide (H2O2), singlet

*Drought Stress: Manifestation and Mechanisms of Alleviation in Plants DOI: http://dx.doi.org/10.5772/intechopen.102780*

## **Figure 5.**

*Production of various ROS by energy transfer (or) sequential univalent reduction of ground state triplet oxygen.*

oxygen (1 O2) and hydroxyl radical (OH• ) are mainly produced by enzymatic or nonenzymatic processes during photosynthesis (**Figure 5**). Their production occurs also in components of electron transport system in the mitochondria by partial reduction or oxidation of atmospheric oxygen [53]. In some current studies, it has been shown that ROS have dual role in plant biology; involvement in vital signaling processes and as toxic by-products of aerobic metabolism [53].
