Salt effect on K influx by two rice cultivars differing in salinity tolerance

Rice cultivars differ in their ability to absorb ions from the soil solution under non-saline conditions. Cultivar differences in kinetic parameters that describe influx of nutrients absorbed through active uptake in response to salinity might be used to develop fertilisation strategies under saline conditions. Potassium depletion studies were conducted to determine the effect of Na and Ca salts on K influx into roots of salt-tolerant (Jasmine 85) and salt-sensitive (Newbonnet) rice cultivars. Depletions could not be described by Michaelis-Menten for Jasmine 85 subjected to 50 mol m(-3) Cl added as NaCl, or for Newbonnet subjected to 50 mol m(-3) Cl of all salts and 25 mol m(-3) Cl as NaCl. Thus, kinetic parameters for these treatments could not be calculated. No salt concentration differences in I-max and Km were calculated for Jasmine 85 subjected to CaCl2 or the combination of NaCl and CaCl2. The I-max value for Jasmine 85 subjected to CaCl2 was 81% greater than for plants subjected to zero salt addition. Values of I-max for Jasmine 85 and Newbonnet for the other salt treatments where I-max was calculated were not different from the zero salt control. Addition of the combination of NaCl and CaCl2, increased Km for Newbonnet by 171% to 5.7 mu mol L-1 compared to plants subjected to zero salt addition. In contrast to Newbonnet, Km values for Jasmine 85 subjected to NaCl decreased by 61% to 3.3 mu mol L-1 Salt addition to Jasmine 85 resulted in apparent increases in C-min levels that were three to six times greater than with no salt addition. Newbonnet subjected to CaCl2 or the combination of NaCl and CaCl2 had C-min levels that were the same as the zero salt control. Results of this experiment suggest that uptake kinetics were affected by salt and appeared to correspond to salt sensitivity of the plant. Potassium influx by the salt-sensitive cultivar was inhibited with salts that contained Na at 25 mol m(-3) Cl. At 50 mol m(-3) C1, influx of K by the salt-sensitive cultivar subjected to additions of Na or Ca was inhibited. Potassium influx by the salt-tolerant cultivar was inhibited with Na salts at the high Cl concentration. For both cultivars, Ca appeared to reduce Na-induced reduction in K uptake in some instances.