PHYSIOLOGICAL-RESPONSE TO SALINITY IN RICE PLANT .2. RELATIONSHIP OF SODIUM EXCLUSION TO TRANSPIRATION AND ROOT-RESPIRATION RATES IN NACL-TREATED RICE PLANT

In order to clarify the relationships of sodium exclusion to transpiration and root-respiration rates in 100 mmol l-1 NaCl-treated rice plant, transpiration stream concentration factor of Na+ (TSCFNa+) was measured at different oxygen concentrations, pH and temperatures of root medium under different humidity conditions. It was confirmed that TSCFNa+ decreased hyperbolically with the increase of the transpiraiton rate, namely, sodium-exclusion efficiency increased with transpiration rate. However, TSCFNa+ and top-Na content were not clearly related to root-respiration. Neither was a difference found in the relationship between TSCFNa+ and transpiration rate measured at 20-degrees-C and 32-degrees-C, and at pH 4.0 and 7.0 of culture solution. These results imply that root respiration is not directly related to the sodium exclusion mechanism. It was shown that the sodium-exclusion mechanism also works for chlorine because of a positive correlation between TSCFNa+ and TSCFCl-. These results suggest that ion exclusion in rice plants may be based on a non-metabolic process and it is important to maintain a high transpiration rate for exclusion and growth under saline conditions.