Co-Authors:
Yermiyahu, U., Department of Field and Vegetable Crops, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot, 76-100, Israel
Nir, S., Seagram Center for Soil and Water Sciences, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot, 76-100, Israel
Ben-Hayyim, G., Institute of Horticulture, The Volcani Center, Bet Dagan, 50250, Israel
Kafkafi, U., Department of Field and Vegetable Crops, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot, 76-100, Israel
Abstract:
The presence of Ca2+ ions in solution is vital for root growth. The plasma membrane is one of the first sites where competition between Ca2+ and other ions occurs. We studied the competition between Ca2+ and Na+ or Mg2+ for sorption sites on the plasma membrane of melon root cells. Sorption of 45Ca2+ to right-side-out PM vesicles of melon (Cucumis melo L.) roots (prepared by aqueous two-phase partitioning) was studied at various Ca2+ concentrations, in the presence of increasing concentrations of Na+ or Mg2+ chlorides. Experimentally determined amounts of Ca2+ sorbed to the plasma membrane vesicles agreed fairly well with those calculated from a competitive sorption model. The best fit of the model to the experimental data was obtained for an average surface area of 370 Å2 per charge, and binding coefficients for Na+, Mg2+ and Ca2+ of 0.8, 9 and 50 m-1, respectively. Our results suggest that nonphospholipid components in the plasma membrane contribute significantly to Ca2+ binding. The high affinity of Ca2+ binding to the plasma membrane found in this study might explain the specific role of Ca2+ in relieving salt stress in plant roots. © 1994 Springer-Verlag New York Inc.
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