Kinetics of Sulfate Absorption by Barley Roots

Open Access
Publisher Website
Google Scholar
Abstract
Barley (Hordeum vulgare) was grown for 5 days over aerated 2 x 10-4 M Ca(H2PO4)2 in the dark at 24[degree] C, after a 24-hr, germination in aerated water. Roots were excised and absorp-tion of S35O4 was studied over a 3 hr. period. Diffusible labeled sulfur was removed by exposing the roots to 10-3 [image] CaSO4 (non-radioactive) for 1 hr., leaving for final measurement the actively absorbed fraction only. Over the concn. range 5 x 10-5 [image] , the rate, v, of SO4 absorption was related to the SO4 concn. ,(S), according to the equation [image] where V is the max. rate at infinite (S) and Ks the "Michaelis constant" of a postulated complex between SO4 and a carrier. The complex is considered to traverse a membrane not permeable to free SO4 ions. At higher concns., the rate of SO4 absorption was higher than expected on the basis of the equation. SeO4 competed with SO4, but H2PO4 and NO3 had no effect on the rate of SO4 absorption. Ca ions increased the rate of SO4 absorption.