The effect of cytokinins on nitrate reductase activity

Cytokinins in addition to nitrate induce nitrate reductase activity (NRA) in some plants. Effects of cytokinins on NRA was investigated in stem pith parenchyma of kale, intact wheat and barley seedlings and isolated cucumber cotyledons. The most profound effect on NRA was found in barley and wheat seedlings. NRA in seedlings sprayed with 100 μM 6-benzylaminopurine (BAP) for three subsequent days was increased in leaves and decreased in roots. These changes were further enhanced in seedlings grown in nutrient solution lacking nitrate: NRA in wheat and barley leaves was increased by 57% and 202%, respectively, in plants supplied with nitrate the NRA increase was not significant: in wheat and barley leaves by 22% and 9%, respectively. Similar effect of BAP and kinetin was found in kale stem parenchyma and cucumber cotyledons. The cytokinin kinetin or BAP alone increased NRA about twice in kale and three times in cucumber. Addition of nitrate to the medium enhanced the effect of kinetin in kale discs, but the two effects were not additive. Additive effect of nitrate and BAP on NRA was found in cucumber cotyledons in light. In general NRA was more affected by cytokinins in intact seedlings of wheat and barley as compared to explanted tissue of kale and cucumber, and lack of nitrogen made their effect more expressive.