NaCl-stress induced alteration in glutamine synthetase activity in excised senescing leaves of a salt-sensitive and a salt-tolerant rice cultivar in light and darkness

Alteration in glutamine synthetase activity was studied in excised senescing leaves of rice (Oryza sativa L.) of a salt-sensitive (Ratna) and a salt-tolerant (Getu) cultivar subjected to NaCl-stress. Glutamine synthetase activity declined during senescence in darkness, but increased initially and then decreased under light treatment, which is correlated with the degree of leaf senescence. In NaCl-stressed leaves the declining trend of this enzyme activity was accelerated in the faster senescing cv. Ratna in both light or darkness. However, it was partially retarded in the dark and fully in the light in the slower senescing cv. Getu. This probably indicates that the control mechanism of enzyme activities is different in the sensitive and the tolerant cultivar under saline condition. The higher activity of glutamine synthetase and consequently higher synthetic activity in the tolerant cultivar may be a biochemical adaptation for salt tolerance in rice.