ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Vacuoles were isolated from leaves of Kalanchoë daigremontiana Hamet et Perrier de la Bathie, and the ionic sensitivity of the vacuolar ATPase was studied in vacuole homogenates desalted on Sephadex G-25. The ATPase activity was dependent on the presence of divalent cations (Mg2+≥ Mn2+≥ Ca2+, Co2+; Zn2+ had no effect). Mg2+-dependent ATPase activity was stimulated by anions (Cl− 〉 malate2+, HCO−3), with maximal stimulation at concentrations above 50 mM. Mg2+-Dependent activity was inhibited by NO−3 above 2 mM, but no saturation was observed up to 100 mM. No stimulation by K+ or Na+ was detected; stimulation by NH+4 was abolished by 0.01% (w/v) Triton X-100, suggesting that the NH+4 effect was due to the permeability of vacuolar membrane vesicles to NH3.Trans-tonoplast electrical potentials (Δψ) and intra-vacuolar pH were measured with glass microelectrodes and antimony covered glass micro-pH-electrodes, respectively. Free vacuofes isolated from Kalanchoë tubiflora (Harv.) Hamet were slightly positive with respect to the suspension medium. This Δψ was insensitive to the protonophore FCCP and depolarized by about 4 mV on addition of 50 mM KCl, still remaining about +5 mV. Upon addition of 7 mM Mg-ATP, vacuoles showed an FCCP-sensitive increase of Δψ from +9.2 ± 2.8 (13) to +17.8 ± 3.7 (12) mV [given as x̄± sd (n)] and an internal acidification from pH 5.4 ± 0.2 (11) to pH 4.3 ± 0.4 (12). Mg-ADP and ATP without Mg2+ had no effect on Δψ.It is concluded that the H4 pumping at the tonoplast is due to the functioning of the anion-sensitive vacuolar ATPase and that this is an essential part of the mechanism of nocturnal acid accumulation in CAM.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1984.tb04594.x
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