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

Abstract

The internal contents and excretion of 3,6,7-trihydroxycoumarin (THC), a UV-absorbing substance, were measured in the green alga Dasycladus vermicularis from southern Spain under different conditions of photosynthetically active radiation (PAR), temperature and salinity in the laboratory. Data were correlated to changes in the effective quantum yield of 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. In some cases, enhanced dissolved THC concentration was correlated to increasing photoinhibition of chlorophyll fluorescence. The results suggest that, apart from the previously reported induction by UV radiation, the excretion of THC in D. vermicularis responds to multiple environmental factors. Both excreted and extracted forms of THC were characterized by means of high-performance liquid chromatography, indicating some changes in the molecule structure as observed by differences in the maximum of the absorption peak. However, no oxidation of the molecule occurs in the excretion process, since a high antioxidant capacity of THC was evident, underlying its possible involvement in the scavenging of oxidized radicals.