Enzymes of Glutamine and Asparagine Metabolism in Developing Wheat Grains

Total protein, glutamate dehydrogenase, and aspartate pyruvate transaminase activities per grain increased during wheat grain development. Glutamate synthase and glutamate-pyruvate transaminase activities increased mainly during the early stages. Asparagine synthetase and glutamate-oxaloacetate transaminase activities declined at maturity. Activity of glutamine synthetase followed a decreasing pattern. Specific activities as well as activities per unit dry weight decreased at maturity. Compared to C-306 (low-protein variety), grains of Shera (high-protein variety) had higher activities of glutamate dehydrogenase, glutamate synthase, glutamate-pyruvate transaminase, and aspartate-pyruvate transaminase during later stages of grain development. It is suggested that in developing wheat grains, both the glutamate synthase cycle and glutamate dehydrogenase pathway may be operative in ammonia assimilation, the former predominating during early stages and the later playing a more active role during the later stages.