NaCl Alteration of Plasma Membrane of Allium cepa Epidermal Cells. Alleviation by Calcium

Abstract

Summary This research was undertaken to study ionic (NaCl) and osmotic (mannitol) effects on the plasma membrane properties of inner epidermal cells of onion bulb scales. The influence of Ca2+ in counteracting the Na-induced cellular alterations was also studied. Cell membrane permeability for individual intact cells and cell viability were determined by the plasmolytic method, and lipid partiality was evaluated. Na+, and not mannitol, a) increased membrane permeability to urea, methylurea and ethylurea, b) decreased membrane partiality to lipid permeators, and c) increased the number of cells showing swollen protoplasm and number of dead cells. These effects resulting from Na+ were prevented by Ca+ when it was added either simultaneously with Na+ or separately after Na+ exposure. The results suggested that NaCl disrupted the plasma membrane structure, which is most probably initiated by the loss of its Ca2+. The protoplasmic swelling is a symptom of salt injury resulting from membrane disruption and subsequent Na+ accumulation in the cytoplasm, which was a consequence of water uptake. A deleterious effect of salinity on the plasma membrane must be attributed to ion toxicity rather than to osmotic stress.