Uptake and Excretion of Dissolved Organic Phosphorus by Two Toxic Dinoflagellates, Alexandrium tamarense Lebour (Balech) and Gymnodinium catenatum Graham

摘要

We performed experiments on the uptake and excretion of dissolved organic phosphorus (DOP) using two toxic dinofiagellates, Alexandrium tamarense Lebour (Balech) and Gymnodinium catenatum Graham, isolated from Hiroshima Bay, Japan. ATP (adenosine triphosphate), UMP (uridine-5-monophosphate), G-6-P (glucose-6-phosphate) and Glycero-P (glycerophosphate) were used as DOP sources in preliminary uptake experiments. ATP was selected as the DOP species for the short-term uptake experiment because preliminary experiments showed it to be the DOP source used by both species. Although the K_s values of A. tamarense and G. catenatum (5.63 and 7.61 mu M, respectively) obtained from the short-term experiments for ATP were only slightly higher than those reportedfor dissolved inorganic phosphorus (DIP), the rho_(max) values (5.04 pmol/cell/h and 13.4 pmol/cell/h, respectively) were much higher. The DOP excretion rate in batch-culture experiments was estimated at 0.084 pmol/cell/h for A. tamarense and 0.012 pmol/cell/h for G. catenatum, accounting for about 30 and 25, respectively, of the assimilated phosphorus. Our results suggest that the DIP-depleted conditions of Hiroshima Bay favor these two species by supporting their ability to use DOP.