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 24h with 200 mmol/dm(3) 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 micro mol/dm(3) 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.