Phosphate uptake by the component parts of Chara hispida

Abstract

Mean daily rates of net phosphate uptake, as determined colorimetrically from phosphate depletion of the medium, were measured for Chara hispida shoots given 1 mmol m^-3 phosphate and isolated (split chamber technique) rhizoid-node complexes given 1-, 50-, 100-, 500- and 1000 mmol m^-3 phosphate. Under aerobic conditions phosphate uptake by the rhizoid-node complex expressed per g FW shoot increased with external phosphate concentration 1–100 mmol m^-3. At external phosphate concentrations 100–1000 mmol m^-3 uptake rates by the rhizoid-node complex were two to three times greater than that for the shoot at 1 mmol m^-3 phosphate. Anaerobic conditions substantially reduced uptake by the rhizoid-node complex. It is concluded that in aerobic sediments, the rhizoid could play a substantial, possibly major role in phosphate uptake by the whole plant but, in aerobic sediments, this will be the case only when phosphate levels in the open water are extremely low.

After 24-h exposure of the whole plant to ³²P-labelled 1 mmol m^-3 phosphate, 99% of the label taken up was found in the shoot. The concentration of labelled phosphorus was similar in apices and lateral branchlets but approximately 30% less in internodal cells. However, after 24-h exposure of detached parts of the shoot, concentrations of label were twice as high in lateral branchlets as in apices or internodal cells. Concentrations in apices were lower when detached; for lateral branchlets the opposite was the case. It is concluded that there is a net transfer of phosphate from lateral branchlets to apices in the intact plant. At an external phosphate concentration of 100 mmol m^-3, 79% of the labelled phosphate taken up by the rhizoid-node complex was translocated to the shoot, where highest concentrations were found in the apices, thus confirming the concept of the meristematic region as a sink.