Influence of calcium on selectivity of ion absorption process

Abstract

Several polyvalent cations affect absorption by excised plant roots similarly to calcium. Magnesium appears to be an exception. It is suggested that either the particular mechanism involved is not specific for calcium or that the polyvalent cations act via a calcium interaction. Calcium was found to have the property of drastically altering the ratio of absorption of scdium and potassium from a mixture of the two. Using lithium and Na + K solutions it was shown that the absorption system was extremely sensitive to smal1 concentrations of calcium. As little as 10/sup -6/ M calcium was suificient to cause a detectable change in absorption rates. The effect of calcium is enhanced in mixtures of sodium and potassium compared to its effect in single salt solutions. The essentially constant sum of the absorptions of sodium and potassium in spite of large changes in the ratio of absorbed sodium and potassium caused by the presence of calcium suggests a common metabolic carrier. The controlling behavior of calcium was found in the roots of six different species of plants. This may indicate a widespread occurrence. (auth)