Modification of plasma membrane and vacuolar H+-ATPases in response to NaCL and ABA

The role of ABA in the modification of membrane proton pump activity in cucumber roots which had been stressed for 24 h with 200 mmol/dm3 NaCl was investigated. It was shown that treatment of plants with salt distinctly increased the activity of the plasma membrane H+-ATPase (EC 3.6.3.6) as well as of the vacuolar H+-ATPase (EC 3.6.3.14). In roots treated with NaCl, an increase of ABA level was observed. Moreover, 24-h treatment of seedlings with 50 μmol/dm3 ABA increased the activity of proton pumps in both membranes. However, when ABA was added to the reaction medium, no changes in ATPase activities were observed. The increased H+-ATPase activity in plasma membranes isolated from the ABA-treated roots was positively correlated with a higher level of PM-H+-ATPase transcript. These data have provided evidence that under salt stress conditions, the role of ABA action due to salinity on the induction of the PM-H+-ATPase could be at the level of gene expression.