Vacuolar H +-ATPase (V-H+-ATPase) has been suggested to play a pivotal role in maintenance of ion homeostasis inside plant cells.In the present study,the expression of V-H+-ATPase genes was analyzed in the roots and leaves of a woody plant Broussonetia papyrifera stressed with 50,100 and 150 mM NaCl.Moreover,the expression and distribution of subunit E protein were investigated by Western blot and immunocytochemistry.It showed that treatment of B.papyrifera with NaCl distinctly changed the hydrolytic activity of V-H+-ATPase in the roots and leaves.Salinity induced a dramatic increase in V-H+-ATPase hydrolytic activity in the roots.However,only slight changes in V-H+-ATPase hydrolytic activity were observed in the leaves.In contrast,increase in H+ pump activity of V-H+-ATPase was observed both in the roots and leaves.In addition,NaCl treatment led to increase in H+-pyrophosphatase (V-H+-PPase) activity in the roots.NaCl treatment triggered enhancement in mRNA levels for subunits A,E and c in the roots,whereas only subunit c mRNA was observed to increase in the leaves.By Western blot and immunocytological analysis,subunit E was shown to be augmented in response to salinity stress in the roots.These findings provided evidence that under salt stress,the increase of V-H+-ATPase activity in the roots was positively correlated with a higher transcript and protein level of V-H+-ATPase subunit E.Taken together our results suggest an essential role for V-H+-ATPase subunit E in plant response to salinity stress.