Kinetic characteristics of photoassimilate translocation in Alaria esculenta (Laminariales,Phaeophyceae)

The kinetics of translocation of ¹⁴C-labeled photoassimilate were studied in the kelp, Alaria esculenta (L.) Grev., using a Geiger-Müller detector-probe to measure radioactivity in the source and sink regions of dumbbell-shaped explants cut from blades. Rapid tracer efflux from the source occurred for 4 days following a pulse of [¹⁴C]bicarbonate, with 40–60% of the initial activity remaining in the source after 10–14 days. Portions of source and sink tissue were analysed for distribution of radioactivity in mannitol, amino-acid, organic-acid and insoluble fractions. About 75% of the radioactivity in both source and sink at the end of the experiments was in soluble organic matter. The translocation velocity of the moving solute front (1.0-1.6 cm·h^-1) was derived from time-course profiles of tracer arriving in Alaria sinks. Relative rates of translocation, calculated from these profiles, yielded skewed curves, with maximum rates of import by the sink occurring 72–96 h after the source was pulsed.