Copper uptake by ryegrass seedlings; contribution of cell wall adsorption

Net copper uptake by cellulose discs, isolated root cell walls, and by live and dead roots of whole ryegrass seedlings, were studied using 64Cu as a tracer. Uptake by cellulose discs stopped after around 10 h while uptake by isolated root cell walls continued for up to 50 h. An initial fast phase of uptake consisting predominantly of cell wall adsorption was similar in live and dead tissue for up to 19 h. A slower phase of uptake continued for up to 50 h, greater in live than in dead tissue, the slower phase of uptake in live tissue consisting of both a living and a dead component. Based on these results, an alternative to the desorption method for estimating the apoplastic contribution to total copper uptake is presented. Time-course studies with seedlings given a variety of growing solution/uptake solution regimes, and the relationship between copper uptake and external copper concentration, for short (4.8 h) and long (42.4 h) term uptakes, suggest that differing contributions of cell wall adsorption and symplasmic absorption may be responsible for differing effects of external copper concentration on uptake being expressed by the same tissue. Water flux had little effect on total uptake of copper although a possible effect on absorption could not be ruled out.