Plant Science & Physiology

Under NaCl-dominated salinity stress, Na+ is the primary cause of the ion-specific damage of many plants such as rice. Therefore, understanding the mechanisms of Na+ uptake and its accumulation in various tissues/ organs is very crucial for enhancing salinity tolerance in rice. In the study, we investigated the uptake of Na+ and K+ through root and their transport up to the leaf in salt tolerant rice cultivar Pokkali and compared with salt sensitive rice cultivar BRRI dhan29 using fluorescence microscopy and flame photometry method. Both the methods confirmed higher uptake of Na+ in both root and leaf of salinity tolerant rice cultivar as compared to the salt sensitive one. Salinity stress also induced higher uptake of K+, partcultarly in the salt tolerant rice cultivar. Through inhibitor analysis it was found that high affinity potassium transporters play significant role in uptake and transport of

Na+ in rice, especially in the sensitive cultivar. However, an upragulation of OsHKT1;5 gene in response to salinity stress in the salt tolerant rice cultivar but not in the sensitive one indicates its significant role in recirculation of toxic Na+ ions from plant cells into the environment. Moreover, plasmamembrane Na+/H+ antiporter gene OsSOS1 and tonoplast Na+/H+ antiporter genes NHX1 and 2 were also unregulated several folds under salinity stress in the salt tolerant rice cultivar as measured by semi-quantitative RT-PCR and qRT-PCR. Upregulation of the genes under salinity stress was also found in the salt sensitive rice cultivar but not as high as in the tolerant one. The results suggest that salt tolerant rice cultivar Pokkali restricts the uptake of Na+ into the roots and its transports into the shoot, and once Na+ enters into the cell it is transported back into the apoplast and/or compartmentalized into the vacuole

conferring better salt tolerance.