Behind the scene: Critical role of reactive oxygen species and reactive nitrogen species in salt stress tolerance

Salinity is one of the most important abiotic factors which affects plant growth and development and reduces crop productivity. Plants have stress tolerance ability to respond to a particular type of stress. For salt stress alleviation, plants retain specific mechanisms, such as activation of signalling cascades, ion channels, receptors, hormonal stimulation, ion exchange, osmolytes and antioxidant enzymes which are involved either directly or indirectly in plant protection. In plants, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in different cell compartments and involved in the "oxidative signalling" mechanism. Based on the recent studies in signalling and mechanisms for salt tolerance in plant, we explored the role of the salt overly sensitive system (SOS) related to antiporters of plasma and mitogen-activated protein kinase (MAPK) cascades. Considering the importance of ROS and RNS, the present review has focused on different aspects and mechanisms that play key role in plants cell signalling network in response to salinity stress. In addition, this review highlights the differential expression of ROS, RNS and various antioxidative enzymes in C3, C4 and CAM plants. Moreover, the strategies for alleviation of salt stress such as magnetopriming, nanopriming, biopriming and arbuscular mycorrhizal fungi (AMF) in plants to achieve improved salt tolerance in crops under field conditions and their effects through ROS and RNS is also discussed. We conclude the review with a discussion of unseen issues and suggestions for future researches.