In most herbaceous plants, NR activity takes place predominantly in the leaves(Scheurwater et al., 2002; Reda et al., 2011). In our results under control conditions, where the plants have free access to nutrients,NR activity was higher in leaves than in roots in all plant combinations at T1 and T2. The reduction of NO 3−in the leaves mayprovide the advantage of enabling the direct use of excess reductants produced by photosynthesis (Pate, 1983).