In our work, the predominant site of NO3−reduction (leaves or roots) was dependent on the water stress intensity and time of exposure. NR activity in leaves decreased considerably in all plant combinations under drought, but especially in ungrafted plants, as well as 5/cul tivar and 8/cultivar plants. However, since NR activity was calculated ona FW basis, and PEG treatment affected the RWC of the leaves, the absolute value of NR activity could be overestimated in these treatments. The utilization of nitrate in the leaves is governed by CO2 fixation (Larsson et al., 1989).