Relation Between Calcium and Strontium Transport Rates as Determined Simultaneously in the Primary Root of Zea mays

Abstract

Root segments of Zea mays 55 mm long, were exposed to nutrient containing Sr85 and Ca45 tracers. Translocation rather than uptake was measured, using a newly-designed glass compartmentation system and validated tracer analytic model. Ca transport from solutions containing between 0.25 and 5.0 m[image] Ca was only slightly affected by concentration, but translocation from 0.25 to 0.05 m[image] solutions was markedly reduced. Maximum transport of Sr from nutrient containing 0.05 m[image] Ca was twice that from 2.5 m[image] Ca, and also twice the maximum calcium transported. Thus, under the condition simulating Ca depletion, i.e., 0.05 m[image] Ca, greater amounts of Sr were transported. In these cases the solutions also contained stable Sr at concentrations between 0.25 and 5.0 m[image]. In simultaneous determinations, the ratio of Sr to Ca moved was exactly equal to the ratio of their concentrations in nutrient solution, and there was no evidence of discrimination. Dinitrophenol reduced transport of Sr and Ca to an equivalent extent, amounting to between 2 and 9% of non-treated control levels.