H+-ATPase and H+-transport activities in tonoplast vesicles from barley roots under salt stress and influence of calcium and abscisic acid

Seedlings of two barley cultivars differing in NaCl sensitivity were treated with low (100 mM) or high (400 mM) concentration of NaCl for 6 days. Tonoplast vesicles were prepared from roots, and H+-ATPase and H+-transport activities associated with tonoplast were assayed. Both H+-ATPase and H+-transport activities in the two cultivars were increased at 100 mM NaCl. These activities also increased in the salt-tolerant cultivar at 400 mM NaCl, but in salt-sensitive cultivar were decreased. In vivo treatment with 10 mM Ca2+ stimulated H+-ATPase and H+-transport activities at two levels of NaCl, however, treatment with 10(-5)M (+/-) abscisic acid (ABA) inhibited these activities. From these results we propose that the increase of the vacuolar H+ pumps in barley roots reflects an adaptation to salt stress. The stimulation of H+-ATPase and H+-transport activities by calcium (Ca) depends mainly on its effect in maintaining stability of membrane under salt stress.