Enhanced H⁺ transport capacity and ATP hydrolysis activity of the tonoplast H⁺-ATPase after NaCl adaptation

Tonoplast enriched membrane vesicle fractions were isolated from unadapted and NaCl (428 millimolar) adapted tobacco cells (Nicotiana tabacum L. var Wisconsin 38). Polypeptides from the tonoplast enriched vesicle fractions were separated by SDS-PAGE and analyzed by Western blots using polyclonal antibodies to the 70 kilodalton subunit of the red beet tonoplast H⁺-ATPase. These antibodies cross-reacted exclusively to a tobacco polypeptide of an apparent molecular weight of 69 kilodaltons. The antibodies inhibited ATP-dependent, NO₃^- sensitive H⁺ transport into vesicles in tonoplast enriched membrane fractions from both unadapted and NaCl adapted cells. The relative H⁺ transport capacity per unit of 69 kilodalton subunit of the tonoplast ATPase of vesicles from NaCl adapted cells was fourfold greater than that observed for vesicles from unadapted cells. The increase in specific H⁺ transport capacity after adaptation was also observed for ATP hydrolysis.