Magnesium uptake by soybeans.

Magnesium contents of soybean (Glycine max) roots increase and the K and Ca contents decrease with increased MgCl(2) concentrations in ambient solutions. The Mg uptake is inhibited when both Ca and K are present in the solution, but not by K or Ca alone. Chloride uptake, which is very low from the MgCl(2) solution, is greatly enhanced by the presence of K. The selectivity against Mg imparted by K + Ca appears to be at an external barrier for cation uptake as shown by its dependence on the presence of Ca in the external solution. The Ca content of roots is influenced only slightly by changes in external Ca concentrations from 10(-4) to 10(-2)m, but that of shoots is greatly enhanced as the Ca concentration is increased or the K concentration is decreased. These effects on Ca contents are explained as arising from transport to the shoot without involvement of vacuoles of root cells.