1996 Fiscal Year Final Research Report Summary
Research on Active Calcium Transport Systems of Plant Vacuoles
| Project/Area Number |
07660106
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
応用微生物学・応用生物化学
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| Research Institution | Nagoya University |
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Principal Investigator |
MAESHIMA Masayoshi Associate Professor School of Agricultural Sciences Nagoya University, 農学部, 助教授 (80181577)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Vacuole / Proton pumps / Ca2+-ATPase / Ca2+ / H+ antiporter / Calcium homeostasis |
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| Research Abstract |
In plant cells, vacuole is the main pool of calcium ions. The concentration of Ca^<2+> in the cytosol is kept at low levels, about a few hundred nanomolar. There are two different active Ca^<2+> transport systems on the plant vacuolar membranes. In this work, we established the assay method for the activity of Ca^<2+> uptake into the vacuolar membrane vesicles and determined the activities of Ca^<2+>-ATP ase and Ca^<2+>/H^+ antiporter individually. The Ca^<2+>/H^+ antiporter is driven by the proton gradient of the membrane vesicles generated by the vacuolar proton pumps. We determined the activity by a membrane filtration method with radioactive ^<45>Ca. Both activities were strongly inhibited by a calcium ionophore A23187. It means that ^<45>Ca was actively transported into the membrane vesicles. The Ca^<2+>-ATP ase and Ca^<2+>/H^+ antiporter exhibited different properties in the Km for Ca^<2+>. The Km values of Ca^<2+>-ATP ase and Ca^<2+>/H^+ antiporter for Ca^<2+> were about 2muM,and 20muM,respectively. The maximal activity of the antiporter was 3-times higher than the Ca^<2+>-ATP ase. From our observation, it was concluded that the Ca^<2+>-ATP ase is a high affinity, low capacity Ca^<2+> transporter, and that the Ca^<2+>/H^+ antiporter is a low affinity, high capacity Ca^<2+> transporter. It is estimated that a large quantity of cytoplasmic Ca^<2+> is taken up by Ca^<2+>/H^+ antiporter. The Ca^<2+>-ATP ase may reduce the cytoplasmic Ca^<2+> concentration less than a micromolar. Now we are sequencing the cDNAs for the Ca^<2+>/H^+ antiporter.
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[Publications] Becker, A., Canut, H., Luttge, U., Maeshime, M., Marigo, G.and Ratajczak, R.: "Purification and immunological comparison of the tonopplast H^+-pyrophosphatase from cells of Catharanthus roseus and leaves from Mesembryanthemum crystallinum performing C^3-photosynthesis and the obligate CAM-plant Kalanchoe daigremontiana." J.Plant Physiol. 146. 88-94 (1995)
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[Publications] Robinson, D.G., Haschke, H.-P., Hinz, G., Hoh, B., Maeshima, M.and Marty, F.: "Immunological detection of tonoplast polypeptides in the plasma membrane of pea cotyledons." Planta. 198. 95-103 (1996)
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[Publications] Fleurat-Lessard, P., Fragne, N., Maeshima, M., Ratajczak, R., Bonnemain, J.L., and Martinoia, E.: "Highly increased expression of vacuolar aquaporin and H^+-ATPase related to motor cell function in Mimosa pudica L." Plant Physiol.(in press). (1997)
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「研究成果報告書概要(欧文)」より
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