Accumulation of Calcium in Exudate of Individual Barley Roots

Metabolic absorption of Ca by plant roots has been reported to be extremely slow in comparison to the alk?li cationis ad Mg (A,77 14, 15, 16). In certain root tissues, metabolic absorption of Ca was difficult to detect if it occurred at all (1, 9, 14, 18). Since the intact plants of most species are known to take up a large amount of Ca, these results appeare(l to support the hypothesis of solute uptake bv bulk flow of the solution (1, 3, 14). In contrast to the above findings, Handley and Overstreet (8) reported a sizeable metabolic absorptioin of Ca by maize root segments 1.8 to 11.8 mm behind the root tip. A small. but nonetheless significant, metabolic absorption of Ca by bulk excised wheat roots has been reported by Johnson and Jacksoni (12). In addition, Lopushinsky (13) reported that Ca was accumulated against a concentration gradient in the exudate of decapitated tomato plants, indicating that a metabolic process was responsible for the movement of Ca. Evans (6) demonstrated that polar transport of Ca in corn roots was under metabolic control. In an attempt to reconcile these differences, the absorption of Ca by excised barley roots has been examined further. In the present study, the accumulation of Ca in the exudate of individual excised barley roots has been compared with the Ca absorption by bulk excised roots. The roots used in this study were essentially the same kind of material as that which showed little or no net metabolic absorption of Ca previous'y reported for excised roots in bulk ( 14).