PHYSIOLOGICAL-RESPONSE TO SALINITY IN RICE PLANT .6. INDUCED SALT-TOLERANCE BY LOW NACL PRETREATMENT

The objective of the study was to investigate the possibility of inducing salt-tolerance in rice by pretreatment with low concentrations of NaCl. At the 6th leaf stage, salt tolerant Kala Rata 1-24 (KRI) and Bhura Rata, and salt susceptible Taichung 65 and IR28 were pretreated with 0, 9, 18, 52 mmol l(-1) NaCl for 14 d, then, growth was analyzed after transferring to 0, 18, 52 and 104 mmol l(-1) NaCl for 7 d. The amount of accumulated Na and cell-wall constituents of the leaf blades, sheaths and stems, and roots of KR1 and IR28 were analyzed. Moreover, the transpiration stream concentration factor (TSCFNa+) of sodium was observed in KR1. The results showed that, except for IR28, the pretreated plants exhibited increased salt tolerance as measured in terms of dry weight increase. The response to pretreatment and the subsequent increase in salt tolerance depended on the variety and on the pretreatment NaCl concentrations. The increase in the capability to grow in high salinity was attributed to the ability of pretreated seedlings to reduce and/or regulate the Na ion accumulation in the shoots and roots. At the same amount of transpiration, the TSCFNa+ of pretreated KR1 was lower than that of the control plant, which implies an increase in the ion exclusion capacity of the roots. In relation, an increase in the amount of lignin in shoot and cellulose in roots were found in pretreated KR1, while cell-wall constituents of IR28 were almost unaffected by pretreatment.