Abstract

High salinity of the soil hinders the plant germination, growth and development. Salt stress causes osmotic stress, nutritional stress, stomatal closure, ion stress, reactive oxygen species accumulation. Nearly one third of the irrigated land is affected by salinity. More than half of the world population depend on rice as staple food source. Soil salinity affects the rice planting and yield. Better understanding of the morphological, physiological and biochemical properties of the rice plant towards the salt stress provide us regulatory mechanisms that control salt stress tolerance. As of now more than 85 QTLs and genes that are associated with salt stress tolerance in rice are identified so far. SKC1 is the first isolated salt stress related QTL in rice that encodes sodium ion transporter. OsNHX1 encoding vacuolar Na+/ H+ antiporter aids in the transport of Na+ that accumulates in the cytoplasm to the vacuole. OsSOS1 is the Na+ efflux transporter that is activated by OsCBL4-OsCIPK24 complex. OsKAT1 and OsAKT2 encode potassium channel proteins that play a role in the absorption of the potassium ions+ by rice roots. Several of the QTLs and the genes are characterized for understanding of the salt stress mechanism. Several studies were conducted in genomics, transcriptomics, proteomics, metabolomics, and epigenetics that enhance our understanding of the salt stress. The data obtained from these studies can be integrated for precise breeding for the development of the salt stress.

One of the recent studies screened OsPM1 containing nearly 30 amino acid residues by using the microarray technology. The analysis of the promoter region revealed that this gene contains multiple cisregulatory elements that respond to the abiotic stress. QT PCR and promoter GUS transgenic plant analysis revealed that OsPM1 was induced by multiple abiotic stress. GFP analysis revealed that OsPM1 was localized in the cell membrane. Overexpression of the OsPM1 resulted in the hypersensitivity of the rice plants to the salt stress but enhanced drought stress. Alternately the plants expressing antisense OsPM1 were hyposensitive to salt stress and weak to the drought stress.

One of the recent studies showed that foliar application of the 24-epibrassinolide replenished the negative effect of the salt stress in the rice seedlings. It also improved the plant growth and the physiology, reduced the oxidative injury, enhanced the antioxidant enzyme and phenolic compounds in ice plants by reducing the endogenous levels of the ABA. It also resulted in the upregulation of the carotenoids and flavonoids genes .