Differential Ion Stimulation of Plasmalemma Adenosine Triphosphatase from Leaf Epidermis and Mesophyll of Nicotiana rustica L.

An ATPase preparation, presumed to be associated with plasma membrane due to the coincidence on isopycnic gradients of cellulase and beta-glucan synthetase at high substrate, has been isolated from the epidermal and mesophyll of tobacco leaf. The ATPase from both tissues was found to prefer ATP over other nucleotides. The pH optimum was 7.0 in the presence of 3 millimolar MgCl(2) and pH 6.5 in the presence of 3 millimolar MgCl(2) and 100 millimolar KCl. Monovalent ion stimulation patterns of the ATPases from these tissues were found to differ and ion accumulation patterns in these tissues reflect this difference: mesophyll accumulated roughly equal amounts of Na(+) and Rb(+) and its plasma membrane ATPase is also equally stimulated by these ions; on the other hand, epidermal ATPase preparations showed a stronger stimulation by Rb(+) than Na(+) and this tissue was found to accumulate Rb(+) in preference to Na(+). Abscisic acid and fusicoccin affected both ATPase activity and ion uptake, the former inhibiting and the latter stimulating these parameters. These data support the hypothesis that the epidermal plasmalemma ATPase is involved in stomatal opening.