POLYAMINE TRANSPORT IN THE SEAWEED ULVA-RIGIDA (CHLOROPHYTA)

The excessive growth of Ulva rigida C. Agardh, a green seaweed present in the Northern Adriatic Sea, is a problem for the inhabitants and th e economy of the region. As information about hormonal control of grow th in seaweeds is scarce, our aim was to investigate the presence of e ndogenous polyamines and their absorption by algal cells and to correl ate the findings with terrestrial plants. Free polyamines (putrescine, spermidine, and spermine) were present endogenously in the algal thal lus at concentrations ranging from 4 to 134 mu M. Putrescine and sperm idine were also present in the seawater in which the alga usually grow s at concentrations between 0 and 0.9 mu M. Uptake of labeled polyamin es occurred, but it was inhibited by cations present in the seawater. Uptake was investigated also by incubation in distilled water. In this case, uptake displayed characteristics similar to those observed in h igher plant systems. Uptake studies in seawater showed that polyamine accumulation in algal cells occurred and that it followed a concentrat ion gradient and displayed linear kinetics. The mechanism proposed tha t of a passive uptake, as indicated also by the inability of metabolic inhibitors to block transport, There was evidence for polyamine bindi ng to external cell sites, but polyamine uptake by protoplasts as well as polyamine translocation and secretion by the whole thallus was als o demonstrated. Since cultured and actively growing thallus discs disp layed a higher uptake ability than freshly collected ones, a role for polyamines in sustaining growth is discussed.