Dynamics of activity and structure of the tonoplast vacuolar-type H+-ATPase in plants with differing CAM expression and in a C3 plant under salt stress

Abstract

Summary. Differences in the activity and structure of the vacuolar H+-ATPase (V-ATPase, EC 3.6.1.3) were investigated in the C3/CAM intermediate plant Kalanchob" blossfeldiana Poellnitz cv. Tom Thumb, with lower or higher expression of CAM, and Hordeum vulgare cv. Carina, grown with or without 150 mM NaC1. In K. blossfeldiana ATP-hydrolysis and H+-transport activity were higher with higher expression of CAM than in plants with very weak CAM. This was mainly due to a larger amount of V-ATPase. Statistical analysis of the diameter of intramembrane particles (IMPs) on freeze-fractures of tonoplast vesicles showed that IMPs were larger in tonoplast vesicle preparations of K. blossfeldiana with strong CAM expression (9.1 nm) than in preparations of K. blossfeldiana with low CAM expression (7.3 nm). As there is evidence that the majority of IMPs on freeze-fractures of tonoplast vesicles corresponds to the V0 domain of V-ATPase, the higher activity of VATPase in K. blossfeldiana with stronger CAM could be a result of additional structural changes in its membrane-integral domain. The higher activity of V-ATPase in K. blossfeldiana with stronger CAM is discussed in relation to the requirement for a higher proton pumping capacity for nocturnal malate accumulation in the vacuole. The ATP-dependent H+-pumping activity in H. vulgare was higher under salt stress than in control plants, while the rates of ATP-hydrolysis and the size of IMPs were not affected by the salt treatment. The data presented here indicate that different mechanisms might increase the transport capacity of V-ATPase to meet the higher requirements of secondary active transport related to CAM expression and adaptation to salt stress.

SOS2 Promotes Salt Tolerance in Part by Interacting with the Vacuolar H+-ATPase and Upregulating Its Transport Activity

“…At least in the case of VHA-B, this appeared to be caused not by an increased amount of SOS2 or VHA-B under salt stress but rather another mechanism that altered binding affinity or stability of the SOS2 interaction with the V-ATPase. This is consistent with other reports showing that the amount of V-ATPase does not change in short-term salt treatments (26,28,46). While it is not known what modification could have altered the binding affinity of SOS2 for the V-ATPase complex, one possibility is posttranslational modification of SOS2 itself.…”

Activity of Ion Transporters and Salt Tolerance in Barley

“…The vacuolar ç + -ATPase (V-ATPase) manifested much larger changes. The activation of V-ATPase in the vesicles isolated from salt-stressed barley seedlings, at invariable ATP-hydrolase activity, was reported earlier [18,19]. We found that such activation of V-ATPase in the salt-tolerant barley cv.…”

“…Such regulation could arise via the modification of c-subunits in the hydrophobic region of V 0 enzyme and the change in the number of these subunits as already established for F 0 F 1 -ATPases [28]. However, in the salt-stressed barley plants, no restructuring was reported in the V 0 domain [18]. Presently we cannot assert which particular mechanism for V-ATPase coupling control is involved in our case.…”

Chill-induced changes in fatty acid composition of tonoplast vesicles from hypocotyls of Vigna unguiculata (L.) Walp.

“…The fresh weight of different parts of seedlings was measured using analytic balance. At the end of treatment (7 days) the hypocotyls from plants were harvested for the isolation of tonoplast-enriched vesicles (Mariaux et al 1997 modified by Otoch et al 2001). …”