Absorption of Magnesium and Chloride by Excised Corn Root

Absorption characteristics of Mg(2+) and Cl(-) were investigated with 5-day-old excised corn (Zea mays) roots. Uptake from both 0.5 and 10 milliequivalents per liter MgCl(2) solutions occurred at steady state rates for the first 6 hours. Inhibition by dinitrophenol and low temperatures established that absorption during this period was metabolically mediated in the absence and presence of Ca(2+). Absorption isotherms indicated dual mechanisms of Mg(2+) and Cl(-) absorption from solutions above 1 milliequivalent per liter. The effect of H(+) on absorption of Mg(2+) and Cl(-) was typical of that generally reported for other plant roots and other ions. In the physiological pH range, Ca(2+) greatly suppressed the rate of Mg(2+) absorption but had little effect on Cl(-). The influence of Ca(2+) on Mg(2+) appeared to be noncompetitive and independent of its effect on membrane permeability.