Changes in leaf nitrate reductase activity in vivo and in vitro during light-dark transitions

Nitrate reductase activity in the leaves of a number of plants after transf er from light to dark was assayed both by in vivo and in vitro methods. The initial activity persisted during the dark phase for a considerable length of time and declined gradually. After exposure to light again, the NR acti vity increased rapidly. The possibility of nitrate assimilation in complete darkness is discussed.