Uptake of magnesium & its interaction with calcium in excised barley roots

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Abstract
Mg was found to be rapidly absorbed by 6-day-old excised barley roots. The absorption of Mg was sensitive to both low temperature and dinitrophenol. In addition, excess Mg absorption was found to be related to organic acid production in the root. These facts establish the metabolic nature of Mg absorption. In general, the absorption of Mg from single salt solutions was more similar to the alkali cations than to Ca. A lag phase was observed in the time curves for Mg uptake. The lag phase could be eliminated by a 30 minute pre-treatment of the roots in a dilute acid solution. It is suggested that there is a labile fraction of the initial Mg content which is easily lost from the root, even to a solution which contains Mg. A large fraction of the Mg absorption was blocked very effectively by small amounts of Ca. The blocking action was quite pronounced, even at Ca concentrations where there was a net loss of Ca from the root. It is proposed that Ca acts by altering the permselective properties of the cell surface region.
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