Excretion of coumarins by the Mediterranean green alga Dasycladus vermicularis in response to environmental stress

The internal contents and excretion of 3,6,7-trihydroxycoumarin (THC) a UV- absorbing substance, were measured in the green alga Dasycladus vermiculari s from southern Spain under different conditions of photosynthetically acti ve radiation (PAR), temperature and salinity in the laboratory. Data were c orrelated to changes in the effective quantum yield or photosynthesis using PAM chlorophyll fluorometry. The concentrations of THC in the thallus were not significantly affected by the different experimental treatments after 24 h of exposure. However. excretion of THC was induced rapidly by high and low PAR irradiances, as well as by high temperature and by low salinity. I n some cases, enhanced dissolved THC concentration was correlated to increa sing photoinhibition of chlorophyll fluorescence. The results suggest that, apart from the previously reported induction by UV radiation, the excretio n of THC in D. vermicularis responds to multiple environmental factors. Bot h excreted and extracted forms of THC were characterized by means of high-p erformance liquid chromatography, indicating some changes in the molecule s tructure as observed by differences in the maximum of the absorption peak. However, no oxidation of the molecule occurs in the excretion process, sinc e a high antioxidant capacity of THC was evident, underlying its possible i nvolvement in the scavenging of oxidized radicals.