Correlation between the Suppression of Glucose and Phosphate Uptake and the Release of Protein from Viable Carrot Root Cells Treated with Monovalent Cations.
Treating carrot (Daucus carota L.) discs with ice-cold NaCl solutions for 30 minutes caused three effects that appear to be functionally related: the exchange of tissue Ca(2+) and Mg(2+) for Na(+), the release of protein, and the suppression of active uptake of glucose and orthophosphate. Cyclosis continued apparently unabated after treatment with NaCl at concentrations of up to 0.25 m, so the cells remained viable and energetically competent. The correlation between the release of Ca(2+) and Mg(2+) and release of protein, and between these effects and the suppression of glucose and orthophosphate uptake, supports the hypothesis that divalent cations maintain, and monovalent cations disrupt, linkages between the outer cell surface and proteins required for active solute uptake. Calcium preserved uptake activity only when it was added in time to prevent the release of protein. Cells gradually recovered some glucose uptake activity after it had been completely inactivated by treatment with 0.25 m NaCl. This recovery occurred in the absence of added Ca(2+). It was inhibited by puromycin and so appears to require some protein synthesis. Beet (Beta vulgaris L.) discs were more resistant than carrot discs to treatment with NaCl solutions, thus reflecting the difference in tolerance of the two species to sodicity.
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United States Salinity Laboratory, Soil and Water Conservation Research Division, Agricultural Research Service, United States Department of Agriculture, Riverside, California 92502.
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