Solute Leakage from the Isolated Parenchyma ofAllium cepaandKalanchoë daigremontiana

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Abstract
Efflux of different solutes from leaf slices of Kalanchoë daigremontiana and from slices of the onion bulb scale was reinvestigated with respect to (1) dependence on turgor, (2) selectivity, (3) integrity of protoplasts and cellular changes. In both materials efflux of solutes (electrolytes or sugars) is non-selective and strongly dependent on turgor. Treatment of tissue slices with hypotonic solutions (below a critical osmotic pressure) resulted in high leakage rates, an increase in free space and an increased number of damaged cells. Low concentrations of calcium did not prevent this loss of retention and cell stability. Part of the surviving cells were found to have a strongly decreased osmotic pressure of cell sap. Leakage did not occur simultaneously at all cells of the tissue slice. It can be concluded that efflux from parenchyma cells in hypotonic solutions results from irreversible osmotic breakdown and reversible membrane defects both favoured by high turgor.