Effects of salinity on sodium content and photosynthetic responses of rice seedlings differing in salt tolerance

Maribel L. Dionisio-Sese, Satoshi Tobita, 'Effects of salinity on sodium content and photosynthetic responses of rice seedlings differing in salt tolerance', Journal of Plant Physiology, vol. 157(1), pp.54-58, 2000

The effects of salinity on four rice (Oryza sativa L.) cultivars differing in salt tolerance were investigated with respect to gas-exchange parameters, chlorophyll fluorescence and Na+/K+ content in the youngest fully expanded leaf. During 1-week treatment at 6 and 12 dS m-1 salinity levels (equivalent to about 60 and 120 mmol/L NaCl, respectively), the salt-sensitive cultivars Hitomebore, IR28 and Bankat, but not the salt-tolerant cultivar Pokkali, showed significant increases in Na+/K+ content with increasing salinization. Salinity caused a substantial reduction in carbon assimilation rate and stomatal conductance in all cultivars. Chlorophyll fluorescence measured in intact leaves showed that the potential photochemical efficiency of PSII (maximum quantum yield F(v)/F(M)) was almost unaffected by salinity, whereas the overall or actual efficiency of photochemical energy conversion (actual quantum yield ?F/F(M)) declined with increasing salinity in all cultivars except Pokkali. The total non-photochemical quenching increased significantly with increasing salinity level in the salt-sensitive cultivars but not in the tolerant Pokkali. These results suggest that salt sensitivity in rice is associated with increased shoot Na+ accumulation, decreased PSII photochemical efficiency, and enhanced non-photochemical quenching.