EFFECT OF CHILLING ON ASSIMILATORY SULFATE REDUCTION AND GLUTATHIONE SYNTHESIS IN MAIZE

The contents of cysteine, gamma-glutamylcysteine and glutathione, as w ell as the activity of enzymes of assimilatory sulfate reduction and g lutathione synthesis in second leaves and root tips of maize seedlings (Zea mays L. cv. LG 11) cultivated at low temperatures, were compared with controls grown at 25 degrees C. In vitro nitrate reductase (EC 1 .6.6.1) activity was measured for comparison. Compared with the contro ls, adenosine 5'-phosphosulfate sulfotransferase activity was 3.5- and 5.5-fold higher at 12 degrees C in second leaves and root tips, respe ctively. After 3 days of growth, the activity of gamma-glutamylcystein e synthetase (EC 6.3.2.2) and glutathione synthetase (EC 6.3.2.3) in t he second leaves was also significantly higher at 12 degrees C compare d with 25 degrees C. Consistent with these enzyme activities, there wa s an increase in cysteine and glutathione contents both in second leav es and root tips after 3 days of growth at 12 degrees C. Nitrate reduc tase activity of second leaves and root tips was not affected by growt h at 12 degrees C, indicating that the increase in adenosine 5'-phosph osulfate sulfotransferase activity and of the enzymes of glutathione s ynthesis was specific. Our results demonstrate that the increased acti vity of a key enzyme of assimilatory sulfate reduction and of the enzy mes of glutathione synthesis contribute to the increased glutathione l evels measured at 12 degrees C.