Biochemical aspects of shoot differentiation in sugarcane callus: I. Nitrogen assimilating enzymes

The developmental patterns of the nitrogen assimilating enzymes were investigated and compared in the non-shoot forming and the shoot forming callus cultures of sugarane. In the shoot forming tissue the pre-emergence period od shoots was characterised by increasing activities of glutamine synthetase and glutamate synthase. The activity of these enzymes during the corresponding period in the non-shoot forming callus was found to decline. Although the activity of glutamate dehydrogenase in the shoot forming callus during the period of pre-emergence of shoots did not show any appreciable change, in the non-shoot forming callus, it increased during the corresponding period. The developmental patterns of nitrate reductase in both the programmes were identical except for the fact that in the shoot forming tissue the nitrate reductase activity was higher at all times than in the non-shoot forming callus. The data suggest that (a) shoot differentiation occurs concomitant with peak glutamine synthetase, glutamate synthase, and nitrate reductase activity, whereas the glutamate dehydrogenase activity is at its lowest, (b) better mobilization of nitrate occurs in the shoot forming callus and (c) the glutamine synthetase/glutamate synthase pathway becomes operative prior to shoot differentiation.