FREE AMMONIA, FREE AMINO-ACIDS, AND ENZYME-ACTIVITY IN MAIZE TISSUE TREATED WITH METHIONINE SULFOXIMINE

Glutamine synthetase and glutamte dehydrogenase activity, free ammonia, and changes in free amino acid pools in tissue of three maize genotypes differing in enzyme activity were measured after 0, 2, 6, 12, and 24 hour incubation with 1 mM methionine sulfoximine (MSX) and 10 mM NH4+ in nutrient solution. Glutamine synthetase activity was almost nil in roots and decreased about 80 percent in shoots after six hr incubation with MSX. Glutamate dehydrogenase activity was not affected by MSX, but was very low in tissue of the -GDH maize mutant. In general, total amino acids decreased with time in MSX. Glutamate in root tissues of the Illinois N6 wild type decreased 80 percent after 24 hr incubation with MSX while it was reduced only 60 percent in the Illinois N6 mutant.