Plant Salt Stress: Adaptive Responses, Tolerance Mechanism and Bioengineering for Salt Tolerance

Salinity is an important abiotic environmental stress factor threatening agricultural productivity throughout the world. The detrimental effects of salinity stress are observed at cellular, organ and whole plant level at osmotic phase (early/short-term response) and ionic phase (late/long-term response). High salinity exerts its negative impact on major plant processes such as disrupting the osmotic and ionic equilibrium, protein synthesis, photosynthesis, energy, and lipid metabolism. To adapt and tolerate salt stress, plants have evolved physiological and biochemical mechanisms orchestrated by multiple biochemical pathways of ion homeostasis, osmolytes synthesis, ROS scavenging, and hormonal balance. At the molecular level, such adaptation involves activation of cascade(s) of gene modulations and synthesis of defense metabolites. In recent years, several candidate genes have been identified and employed to facilitate genetic engineering efforts to improve salt tolerance in crop plants. However, there is a further need of improvement for successful release of salt tolerant cultivars at the field level. In this article we present the physiological, biochemical and molecular signatures of plant responses to salinity, and outline their use in genetic engineering to improve salt stress tolerance.