Influence of cytokinins and phytochrome on nitrate reductase activity in etiolated leaves of maize

Of the different hormones tested, cytokinins stimulated nitrate-induced nitrate reductase (NR) activity in the dark. The optimal stimulation was obtained at 16 hr and this was sensitive to tungstate, 6-methylpurine and cycloheximide. The cytokinin stimulation of NR activity was further enhanced by brief irradiation with red light, but this effect was not noticed when leaves were exposed to far-red light. Both kinetin and red light, when given together, or given with a darkness interruption, stimulated the NR activity more than with either of them alone.