Influence of drought stress on photosynthetic characteristics and protective enzymes in plants

Drought stress as one of the major growth limiting factors in natural environments influences photosynthetic components and electron transfer process, elevating the production of reactive oxygen species (ROS), leading to damage to the cell. Furthermore, ROS are toxic by-products resulted from stress and are involved in signaling pathways, causing major transcriptional changes. ROS scavenging enzymes, localized in the thylakoid membrane of chloroplasts, play a key role in the detoxification of ROS. The capacity of ROSscavenging enzymes depends on several factors including plant species, duration and intensity of drought stress, stages of plant development, and gene expression patterns of various isoforms. In this regard, novel functional and regulatory genes related to ROS-scavenging enzymes in plants are identified that play a key role in response to drought stress. These genes are differentially expressed in sensitive and tolerant species that may be related to the drought tolerance level of plant species themselves; but the overexpression of those genes in transgenic plants mainly improves drought stress tolerance. However, in some conditions, high drought stress severely damages the photosynthesis apparatus. This damage has a direct relationship to photochemical activities of both PSII and PSI that are required for protecting photosystems against photoinhibition. The photosystem protections are related to precise regulation in D1 protein accumulation under high light conditions, contributing to avoid excessive ROS accumulation. This review describes the influence of drought stress on photosynthetic characteristics, also discusses that the overexpression of genes associated with ROS scavenging enzymes in transgenic plants results in higher drought tolerance and improved photosynthetic characteristics.