Carbon exchange between Polysiphonia lanosa (Rhodophyceae) and its brown algal host

Polysiphonia lanosa and its preferred Ascophyllum nodosum host exchange 14C-labeled photoassimilates. Exchange was demonstrated by injecting 14C-bicarbonate into air bladders on 15-30 cm cultured sections of field-collected host blades. Each section bore rhizoidally attached Polysiphonia. In a separate set of experiments, Polysiphonia on similar host material was surface treated with 14C-bicarbonate in sealed vessels. Movement of radioactive label was detected by autoradiographic and liquid scintillation techniques. On average, 10.5% of total label moved from host to hemiparasite following the first treatment, and 9.7% moved from hemiparasite to host following the second. Reciprocal exchange of tagged photoassimilates may play an important role in the specificity of the relationship between these two algal species.