Plant Responses in Saline and Arid Environments: An Overview.

Salinity is the most serious threat to agriculture and to the environment in many parts of the world. It is estimated that over 6% of the world's land is affected by either salinity or sodicity. Using saline lands for conventional agriculture requires either improving the soil or enhancing the salt tolerance limit of field crops, the majority of which cannot survive with the levels of average soil salinity prevailing in the fields. Plants exposed to salt stress undergo changes in their environment. The ability of plants to tolerate salt is determined by multiple biochemical pathways that facilitate retention and/or acquisition of water, protect chloroplast functions, and maintain ion homeostasis. Essential pathways include the synthesis of osmotically active metabolites, specific proteins and certain free radical scavenging enzymes that control ions and water flux and support scavenging of oxygen radicals or chaperones. The ability of plants to detoxify radicals under conditions of salt stress is probably the most critical requirement. Many salt-tolerant species accumulate metabolites which play crucial dual roles as osmoprotectants and as radical scavengers. In this paper, plant responses to salinity stress are reviewed with emphasis on physiological and biochemical mechanisms of salt tolerance. Understanding the biochemical and physiological plant responses to salinity may favour the identification of new salt-tolerant cultivars or species and it provides a framework to identify breeding targets for improving salt tolerance. This review may help in interdisciplinary studies to assess the ecological significance of salt stress.