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 excisedsenescing leaves of rice (Oryza sativa L.) of asalt-sensitive (Ratna) and a salt-tolerant (Getu) cultivar subjected toNaCl-stress. Glutamine synthetase activity declined during senescence indarkness, but increased initially and then decreased under light treatment,which is correlated with the degree of leaf senescence. In NaCl-stressed leavesthe declining trend of this enzyme activity was accelerated in the fastersenescing cv. Ratna in both light or darkness. However, it was partiallyretarded in the dark and fully in the light in the slower senescing cv. Getu.This probably indicates that the control mechanism of enzyme activities isdifferent in the sensitive and the tolerant cultivar under saline condition. Thehigher activity of glutamine synthetase and consequently higher syntheticactivity in the tolerant cultivar may be a biochemical adaptation for salttolerance in rice.