Tolerant root stocks (12 and 14) showed increased root NR activity at only T 2 in 7% PEG, although to a lesser extent. This couldbe because the remaining water transpiration flux (highest E val-ues) enables reductions through the NO 3−transport to the leaves.The significant increase in root NR activity may indicate that nitrate flux to roots was not restricted by water stress and that active NO 3−reduction occurs in the roots, possibly due a minor transpiration flux to leaves.