Molecular Insights into the Role of Reactive Oxygen, Nitrogen and Sulphur Species in Conferring Salinity Stress Tolerance in Plants

Salinity stress is the major abiotic stress that affects crop production and productivity as it has a multifarious negative effect on the growth and development of the plant. Salinity stress stimulates the accumulation of reactive oxygen species (ROS) which is toxic to cells at higher concentrations. At lower concentrations, these molecules help in the mitigation of salinity stress through a series of signal transduction mechanisms. The respiratory burst by NADPH oxidase leads to an increase in ROS generation. It is a key signalling node in the plant gene network and helps to integrate the signal transduction with ROS signalling. Reactive nitrogen species (RNS) are free radical and non-radical reactive molecules that are also produced under salinity stress and lead to nitrosative stress by regulating SOS, MAPK dependent, Ca2+ dependent and G-protein dependent pathways. The reactive sulphur species (RSS) is a strong oxidizing agent that preferably attacks the thiol functional group. Activation of the different signalling components like ROS, RNS, RSS, SOS, Calcium, MAPK signalling and cross-talk between different signalling pathways and phytohormones have been considered as the main mechanism for ion homeostasis and Na+ exclusion at the cellular level. These reactive species and their interaction upregulate the gene expression and phosphorylation level of different membrane transporters viz., PM H+-ATPase and Na+/ H+ antiporter which might endure salinity tolerance in plants. This review aims to describe the interplay/crosstalk amongst reactive species and phytohormones under salinity stress. Moreover, mechanistic insight of reactive species-mediated stress regulation and the response has also been discussed which will be helpful for the development of stress-tolerant cultivars.