Role of Internal Potassium in Maintaining Growth of Cultured Citrus Cells on Increasing NaCl and CaCl2 Concentrations

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Abstract
Shamouti orange (Citrus sinensis L. Osbeck) salt-tolerant cells were grown under low water potential conditions induced by polyethylene glycol (PEG), NaCl, and CaCl2. On the basis of equal osmotic potentials, PEG was the least inhibitory, NaCl next, and CaCl2 the most inhibitory. The relation between growth capacity and ion content can be summarized as follows. (a) Internal K+ concentration was a major factor which changed in the presence of PEG, NaCl, and CaCl2 and probably played a key role in determining growth capacity. (b) Internal concentrations of Na+, Ca2+, or Cl- could not be directly correlated with growth. (C) Internal Mg2+ concentration could be significant only on the presence of high external Ca2+ concentrations. (d) The contribution of nitrate and phosphate to the internal osmoticum was negligible. The ratio of external (Ca2+)/(Na+)2 concentration is crucial for growth. Ratios above 0.5 .times. 10-4 per millimolar gave maximal protection from adverse effects of NaCl. Growth capacity was found to be determined by the combination of (Ca2+)/(Na+)2 ratio and the absolute external concentration of NaCl. However, a correlation between internal K+ concentration and growth capacity seemed independent of external NaCl concentration.