Nitrogen Modulates the Diurnal Regulation of Nitrate Reductase in Wheat Plants - Projections Towards Climate Change

This study investigates whether the diurnal regulation of nitrate reductase activity in the flag leaf of wheat is affected by combined increases of C02 and temperature in the air and to ascertain whether the nitrogen supply tnodifies these effects. Spring wheat was grown at ambient (360 pmol mol-') or elevated (700 pmol mol-') C02, under ambient and 4°C warmer temperatures, and with two levels of nitrogen supply in field temperature gradient chambers. At ear emergence, NR activity reaches a maximum in the early part of the light period and declines later in the light period and during the first part of the night. Although elevated COZ did not increase NR activity, it led to a modification of the diurnal regulation. During the last part of the photoperiod the decline of the activity was faster in plants grown in ambient Coz, in which the accumulation of amino acids was higher. The maximum reached in the first hours of the light period in plants grown in elevated COZ and nitrogen abundance was related to a higher accumulation of soluble carbohydrates. The dark inactivation of NR was prevented in plants grown in elevated COZ with low nitrogen. Additionally, the higher decline of NR activation in plants grown with ample nitrogen supply and higher temperatures was related to the accumulation of amino acids. It is concluded that nitrogen plays a role in the activity and posttranslational regulation of NR under the future climatic scenario