Accumulation of Calcium in Exudate of Individual Barley Roots

Abstract

The accumulation of Ca in the xylem exudate from individual excised barley roots (Hordeum vulgare) occurred against a concentration gradient over a wide range of ambient concentrations. The concentration of Ca in the exudate ranged up to 58 times that of the ambient, and this was taken as evidence of a meta-bollcally mediated process. The rate of Ca accumulation in the exudate was compared to the rate of net uptake of Ca by bulk excised roots and was found to be 35 times more rapid at an ambient concentration of 5 meq/liter. It was concluded that the majority of the root cells were not active in Ca absorption and that a group of cells such as the endo-dermis was responsible for Ca accumulation into the xylem. It is suggested that the endodermie constituted a barrier to the free movement of ions across the root and that Ca moved metabolically across this barrier.