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

High fluence PAR (photosynthetically active radiation, 400-700 nm), UV-A (320-400 nm), and UV-B (280-320 nm) radiation were tested for their ability to stimulate the production of UV-absorbing mycosporine-like amino acids (MAAs) in 6 diverse species of marine phytoplankton.Dunaliella tertiolecta, Thalassiosira weissflogii, Pyramimonas parkeae.Pavlova gyrans and Isochrysis sp. were grown under (1) low fluence PAR (LL, 23 to 75 pm01 photons m-2 S-'), (2) high fluence PAR (HL, 255 to 290 11mol photons m-2 S-'), (3) PAR+UV-A (240 to 268 pm01 photons m-' S-' and 4910 mW m-', respectively) 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 levels of PAR and UV radiation were used in the other treatments UV-B supplementation caused a significant depression (23-57 %) in the chl a-specific growth rate of all species except P gyrans, which received the second lowest UV-B dose.The quantum yield of fluorescence for photosystem I1 declined by 4-17 % with exposure to UV-A and/or UV-A+UV-B.The 2 prymnesiophytes exhibited the highest and the dinoflagellate the lowest resistance to UV-B radiation.In vivo absorption spectra indicated that only P. gyrans has a pronounced UV maximum.Of the 3 MAA compounds detected in P. gyrans, only 1 with peak absorption in the UV-A range was photoinducible.The other species examined exhibited relatively small in vlvo UV absorption peaks.In these species, only 1 MAA was detected, a compound with peak absorption in the UV-B range and limited inducibility.UV-B radiation more effectively induced MAAs 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-A+UV-B radiation.Relative to LL cells, UV-B-exposed P. gyrans exhibited a 145-fold MAA increase accompanied by an l l-fold increase in the in vivo UV absorption.In all other species HL had minimal or no effect on MAA production.UV-A radiation effectively increased the chl a-specific MAA content in Isochrysis sp.(77%).T weissflogii (73%), and P. parkeae (43%), and UV-B supplementation 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 significant amounts of these compounds through photoinduction is limited to certain species or taxa, particularly some prymnesiophytes and dinoflagellates