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. 1985 Dec;79(4):1111–1117. doi: 10.1104/pp.79.4.1111

A Ca2+/H+ Antiport System Driven by the Proton Electrochemical Gradient of a Tonoplast H+-ATPase from Oat Roots 1

Karen S Schumaker 1, Heven Sze 1
PMCID: PMC1075037  PMID: 16664540

Abstract

Two types of ATP-dependent calcium (Ca2+) transport systems were detected in sealed microsomal vesicles from oat roots. Approximately 80% of the total Ca2+ uptake was associated with vesicles of 1.11 grams per cubic centimeter and was insensitive to vanadate or azide, but inhibited by NO3−. The remaining 20% was vanadate-sensitive and mostly associated with the endoplasmic reticulum, as the transport activity comigrated with an endoplasmic reticulum marker (antimycin A-insensitive NADH cytochrome c reductase), which was shifted from 1.11 to 1.20 grams per cubic centimeter by Mg2+.

Like the tonoplast H+-ATPase activity, vanadate-insensitive Ca2+ accumulation was stimulated by 20 millimolar Cl− and inhibited by 10 micromolar 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid or 50 micromolar N,N′-dicyclohexylcarbodiimide. This Ca2+ transport system had an apparent Km for Mg-ATP of 0.24 millimolar similar to the tonoplast ATPase. The vanadate-insensitive Ca2+ transport was abolished by compounds that eliminated a pH gradient and Ca2+ dissipated a pH gradient (acid inside) generated by the tonoplast-type H+-ATPase. These results provide compelling evidence that a pH gradient generated by the H+-ATPase drives Ca2+ accumulation into right-side-out tonoplast vesicles via a Ca2+/H+ antiport. This transport system was saturable with respect to Ca2+ (Km apparent = 14 micromolar). The Ca2+/H+ antiport operated independently of the H+-ATPase since an artifically imposed pH gradient (acid inside) could also drive Ca2+ accumulation. Ca2+ transport by this system may be one major way in which vacuoles function in Ca2+ homeostasis in the cytoplasm of plant cells.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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