Effects of xylopine on physiological activities of Scenedesmus obliquus

Xylopine, an aporphine alkaloid contained in the bark of Xylopiadiscreta strongly inhibits growth of Scenedesmus obliquus; 50%inhibition was caused by 2x10^–5 M of xylopine. Photosynthesis was also strongly inhibited by xylopine at concentrationsabove 10^–4 M. Effects on photosynthesis, however, differeddepending on the ratio of alkaloid concentration to cell concentrationin the reaction mixture, so that under certain experimentalconditions with concentrations of xylopine below 10^–4M, there was some acceleration of photosynthesis. Xylopine strongly inhibited the HILL reaction with benzoquinoneas the HILL oxidant. Respiration was not affected at concentrationscompletely inhibiting photosynthesisd growth of the alga. A probable role of the aporphine alkaloid in controlling lichengrowth in nature is discussed. (Received March 25, 1970; )