Photosynthetic and cellular responses in plants under saline conditions

Abstract Salinity is one of the major challenges that the current agricultural system is facing. High salt concentration inhibits the uptake of water by plants and interrupts the cellular ions equilibrium resulting in osmotic stress, ion toxicity, and production of reactive oxygen species (ROS). It inhibits photosynthesis, disrupts the metabolic balance, and damages cellular structures, and ultimately results in the reduction of crop yield. It constrains the activity of the photosystem II complex and induces the loss of chlorophyll pigments. The indepth knowledge of the cellular and molecular mechanisms involved in plant tolerance to salinity can help to identify the candidate genes/proteins that mitigate crop losses due to high salt conditions in the soil. To minimize the salinity-induced damage plants possess some innate defense systems such as synthesis of osmolytes to maintain cell turgor, regulation of ion homeostasis to cater to ions imbalance in the cell, activation of the antioxidant system to limit excessive ROS generation, and maintain the cellular redox balance. At the molecular level, salt stress stimulates various transcriptions factors (AP2/ERF, bZIP, NAC, MYB, WRKY) and regulates the gene expression of both enzymatic (superoxide dismutase, peroxidase, catalase, ascorbic peroxidase, etc.) and nonenzymatic components (ascorbic acid, glycine betaine, tocopherols, flavonoids) of the antioxidant machinery, ion transporters (High-affinity K+ transporters, Na+/H+ exchanger, salt overly sensitive, etc.), photosynthesis-related proteins (OEE, cytochrome b6f, CAB, RuBisCO, etc.), proteins concerned with carbohydrate and energy metabolism (ATP synthase, GAPDH, citrate synthase, malate dehydrogenase, etc.) and signaling proteins (14-3-3-like proteins, annexin, calreticulin, etc.) to reduce the adverse effects induced by salinity especially in halophytes. In this chapter, recent advances on the deleterious effect of salinity on the plant processes and the various tolerance mechanisms used by plants are discussed. Besides, the latest integrative analysis of transcriptomics and proteomics, studies of plants under salinity stress were further taken into account to strengthen the understanding of plant response to salinity.