Abstract
Vacuoles of Japanese artichoke (Stachys sieboldii) tubers accumulate up to 180 mM stachyose ([alpha]-galactose-[1->6]-[alpha]-galactose-[1->6]-[alpha]-glucose-[1 <->2]-[beta]-fructose) against a concentration gradient, probably by means of an active stachyose/H+ antiporter situated on the tonoplast. The goal of this study was to use isolated tonoplast vesicles to provide further evidence for the existence of such a transport mechanism. Therefore, vesicles were prepared from purified vacuoles of dormant tubers. ATP- and pyrophosphate (PPi)-dependent fluorescence quenching of the [delta]pH probe 9-amino-6-chloro-2-methoxyacridine (ACMA) indicated that these vesicles were capable of building up a pH gradient ([delta]pH, inside acid). The potent V-type H+-ATPase inhibitor bafilomycin prevented the formation of a [delta]pH in the vesicles. Bafilomycin (as well as nitrate, but not vanadate) also inhibited ATP hydrolysis, confirming the tonoplast origin of the isolated vesicles. Addition of stachyose (or sucrose, but not of mannitol) to energized vesicles caused a recovery of ACMA fluorescence, indicating a sugar-dependent dissipation of [delta]pH. The rate of fluorescence recovery was dependent on the external sugar concentration used. It displayed a single saturable response to increasing sugar concentrations. Apparent Km values of 52 and 25 mM were computed for stachyose and sucrose antiporter activities, respectively. It was also demonstrated that energized vesicles showed a much higher rate of [14C]stachyose (3 mM) and [14C]sucrose (1 mM) uptake than deenergized vesicles. The results obtained with isolated tonoplast vesicles were very similar to those obtained earlier with intact vacuoles and, therefore, confirm the existence of active stachyose and sucrose/H+ antiporters on the tonoplast of Stachys tuber vacuoles.
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Selected References
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- Blumwald E., Poole R. J. Kinetics of Ca/H Antiport in Isolated Tonoplast Vesicles from Storage Tissue of Beta vulgaris L. Plant Physiol. 1986 Mar;80(3):727–731. doi: 10.1104/pp.80.3.727. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bowman E. J., Siebers A., Altendorf K. Bafilomycins: a class of inhibitors of membrane ATPases from microorganisms, animal cells, and plant cells. Proc Natl Acad Sci U S A. 1988 Nov;85(21):7972–7976. doi: 10.1073/pnas.85.21.7972. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bradford M. M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. doi: 10.1006/abio.1976.9999. [DOI] [PubMed] [Google Scholar]
- Briskin D. P., Thornley W. R., Wyse R. E. Membrane Transport in Isolated Vesicles from Sugarbeet Taproot : II. Evidence for a Sucrose/H-Antiport. Plant Physiol. 1985 Aug;78(4):871–875. doi: 10.1104/pp.78.4.871. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bush D. R., Sze H. Calcium transport in tonoplast and endoplasmic reticulum vesicles isolated from cultured carrot cells. Plant Physiol. 1986 Feb;80(2):549–555. doi: 10.1104/pp.80.2.549. [DOI] [PMC free article] [PubMed] [Google Scholar]
- WILKINSON G. N. Statistical estimations in enzyme kinetics. Biochem J. 1961 Aug;80:324–332. doi: 10.1042/bj0800324. [DOI] [PMC free article] [PubMed] [Google Scholar]