Reactive nitrogen species: Paradigms of cellular signaling and regulation of salt stress in plants

Reactive nitrogen species (RNS) have gained a significant attention in recent years due to their indispensable role in mechanisms regulating various biological processes of plant growth and development under normal as well as in stress conditions. RNS, including nitric oxide, nitrogen dioxide, nitrous acid, peroxynitrite, and dinitrogen tetroxide play a pivotal role in seed dormancy and germination, plant growth and development, stomatal movements, reproduction and pollen tube growth, aging and senescence, as well as in plant responses to environmental stresses. Current review aims to accentuate on the position of RNS in plant response and adaptation to salt stress through various local and systemic signal transduction pathways. The generation of RNS or exogenous application of nitric oxide (NO) donor under salt stress and their inter- and intra-molecular mechanisms in plants are reviewed. Moreover, under salt stress the interplay between RNS and other signaling pathways such as the regulation of ion homeostasis through salt overly sensitive (SOS) pathway, G-protein linked signaling and calcium-dependent signaling will be discussed. The precise role of long-distance signaling and regulation of RNS molecules through post-translational modifications of proteins and fatty acids in the salt stress context will be highlighted. The recent progress and research gaps in the RNS signaling under salinity, the crosstalk of RNS with reactive oxygen species (ROS) and several phytohormones such as auxin, gibberellin, abscisic acid, and salicylic acid will be discussed. The present review will provide an overall update on the involvement of RNS in salt stress response mechanisms and highlight its applications in the development of salt stress-tolerant plants.