Fluctuations in spinach leaf nitrate reductase during light-dark transitions

In vivo nitrate reductase (NR) activity declined gradually either in absence or presence of Mg2+ In dark grown plants of spinach. The increased sensitivity of the extracted NR from the dark grown plants to Mg2+ and ATP is indicative of the post-translational modification as one of the mechanisms to control NR activity. The response of extracted NR was gradual and not instantaneous suggesting a complex interplay of NR regulation, as the dark acclimatized plants when exposed to light caused significant nitrate reduction within 15 min of light exposures even in the presence of Mg2+ and ATP.