Effects of Ca Upon Metabolic and Nonmetabolic Uptake of Na and Rb by Root Segments of Zea mays

Abstract
The results obtained support the hypothesis that Ca exerts 2 antagonistic effects. The 1st effect is inhibiting and results from a modification of the permeability of the outer cell membrane. This effect reduces the nonmetabolic penetration rates of K, Na, and Rb. The 2nd effect is stimulatory and results from an involvement of Ca with metabolic uptake mechanisms. The site of this effect apparently lies deeper in the cell than the plasmalemma. Only the 1st effect was demonstrated for Na uptake. Both effects are apparent in the effect of Ca upon Rb uptake and K depletion.