Effects of salinity on sodium content and photosynthetic responses of rice seedlings differing in salt tolerance
2000
Dionisio-Sese, M.L. | Tobita, S.
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 deltaF/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.
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