Radial Movement of Calcium and Magnesium to the Xylem in Roots of Zea mays

Abstract

The appearance of calcium and magnesium in xylem exudate of excised roots of Z. mays seedlings has been used to compare movement of the two ions from the external solution to the xylem vessels. The ratio of calcium to magnesium in exudate was found to be higher than the ratio of the ions absorbed by the root, indicating a preference of root cells for magnesium over calcium. Whilst both ions follow a radial pathway predominantly in the apoplast, the capacity of plants for discriminatory absorption and transport of the two ions would appear to lie in differential absorption by the root cells of the ions moving in the apoplast.