Increase in Proton-Transport Activity of Tonoplast Vesicles as an Adaptive Response of Barley Roots to NaCl Stress

H+-Transport activity of the vesicles prepared from barley roots was studied at the early phase after application of NaCl stress. The activity reached maximal level at 3 days after the treatment with 200 mM NaCl which moderately reduced the growth. This activity increase could be suppressed in the presence of cycloheximide and actinomycin D. The properties of the membrane vesicles associated with H+-transport activity prepared from both control and NaCl-stressed roots suggested that it was of tonoplast origin based on the following findings: optimal pH at 7.5, strong inhibition by nitrate but not by vanadate, and stimulation by chloride. The density gradient centrifugation of vesicles with Dextran T70 did not show any detectable difference in the distribution patterns of H+-transport activities between control and NaClstressed roots. Furthermore, Km values for ATP of the H+-transport activity of vesicles prepared from control and NaCl-stressed roots were the same. Therefore, H+-transport activity with properties similar to those of the control roots was increased by NaCl stress. The results are discussed in terms of an adaptive mechanism of barley against salt stress.