Preferential Absorption of Potassium by Leaf Tissue of the Mangrove, Avicennia Marina: An Aspect of Halophytic Competence in Coping with Salt

Abstract

One aspect of the salt tolerance of the mangrove, Avicennia marina, was investigated: the preferential absorption of potassium by leaf tissue in the presence of high concentrations of salt (sodium chloride). The rate of absorption of potassium, over the concentration range 0·02 to 1·5 mM, follows the Michaelis-Menten relation, approaching the theoretical maximum, V max, at 1· 5 mM. The apparent Michaelis constant is 0·20 mM. At higher concentrations, up to 50 mM potassium, the rate of potassium absorption reaches values several times higher than the theoretical maximum calculated on the basis of the relation applying over the low range of concentrations, indicating the operation of a second mechanism of absorption. At both low (1 mM) and high (10 mM) concentrations of potassium, its absorption was little affected by sodium chloride concentrations up to 200 mM. At 10 mM potassium, sodium chloride at concentrations up to and including 500 mM (more than its concentration in sea.water) failed to interfere with the absorption of potassium.