Glutathione synthesis in maize genotypes with different sensitivities to chilling

The effect of chilling on enzymes, substrates and products of sulfate reduction, glutathione synthesis and metabolism was studied in shoots and roots of maize (Zea mays L.) genotypes with different chilling sensitivity. At full expansion of the second leaf, chilling at 12° C inhibited dry weight increase in shoots and roots compared to controls at 25° C and induced an increase in adenosine 5´-phosphosulfate sulfotransferase and γ-glutamylcysteine synthetase (EC 6.3.2.2) activity in the second leaf of all genotypes tested. Glutathione synthetase (EC 6.3.2.3) activity was about one order of magnitude higher than γ-glutamylcysteine synthetase activity, but remained unchanged during chilling except for one genotype. During chilling, cysteine and glutathione content of second leaves increased to significantly higher levels in the two most chilling-tolerant genotypes. Comparing the most tolerant and most sensitive genotype showed that chilling induced a greater incorporation of 35S from 35S-sulfate into cysteine and glutathione in the chilling-tolerant than in the sensitive genotype. Chilling decreased the amount of35S-label incorporated into proteins in shoots of both genotypes, but had no effect on this incorporation in the roots. Glutathione reductase (EC 1.6.4.2) and nitrate reductase (EC 1.6.6.1) activity were constitutively higher in the chilling-tolerant genotypes, but showed no changes in most examined genotypes during 3 d at 12° C. Our results indicate that in maize glutathione is involved in protection against chilling damage