Photoinduction of UV-absorbing compounds in six species of marine phytoplankton

High fluence PAR (photosynthetically active radiation, 400-700 nm), UV-A (3 20-400 nm), and UV-B (280-320 nm) radiation were tested for their ability t o stimulate the production of UV-absorbing mycosporine-like amino acids (MA As) in 6 diverse species of marine phytoplankton. Dunaliella tertiolecta, T halassiosira weissflogii, Pyramimonas parkeae, Pavlova gyrans and Isochrysi s sp, were grown under (1) low fluence PAR (LL, 25 to 75 mu mol photons m(- 2) s(-1)), (2) high fluence PAR (HL, 255 to 290 mu mol photons m(-2) s(-1)) , (3) PAR+UV-A (240 to 268 mu mol photons m(-2) s(-1) and 4910 mW m(-2), re spectively) and (4) PAR+UV-A+UV-B (103, 216, or 304 mW m-2 weighted UV-B). Amphidinium carterae was grown under similar conditions in LL but reduced l evels of PAR and UV radiation were used in the other treatments. UV-B suppl ementation caused a significant depression (23-57 %) in the chi a-specific growth rate of all species except P. gyrans, which received the second lowe st UV-B dose. The quantum yield of fluorescence for photosystem II declined by 4-17 % with exposure to UV-A and/or UV-A+UV-B. The 2 prymnesiophytes ex hibited the highest and the dinoflagellate the lowest resistance to UV-B ra diation. In vivo absorption spectra indicated that only P, gyrans has a pro nounced UV maximum. Of the 3 MAA compounds detected in P. gyrans, only 1 wi th peak absorption in the UV-A range was photoinducible. The other species examined exhibited relatively small in vivo UV absorption peaks. In these s pecies, only 1 MAA was detected, a compound with peak absorption in the UV- B range and limited inducibility. UV-B radiation more effectively induced M AAs than UV-A or HL in 4 of the 6 species. In P, gyrans large increases in the concentration of the inducible MAA were obtained with HL and with UV-AUV-B radiation. Relative to LL cells, W-B-exposed P. gyrans exhibited a 145 -fold MAA increase accompanied by an Ii-fold increase in the in vivo UV abs orption In all other species HL had minimal or no effect on MAA production. UV-A radiation effectively increased the chi a-specific MAA content in Iso chrysis sp. (77%), T. weissflogii (73%), and P, parkeae (43%), and UV-B sup plementation increased it by a further 141% in Isochrysis sp, and 95 % in P . parkeae. On a cell volume basis, UV-B also approximately doubled the MAA concentration in the latter 2 species. We conclude that, although MAAs may be commonly present in phytoplankton cells, an ability to produce significa nt amounts of these compounds through photoinduction is limited to certain species or taxa, particularly some prymnesiophytes and dinoflagellates.