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Marine Ecology Progress Series

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MEPS 132:287-297 (1996)  -  doi:10.3354/meps132287

Acclimation of phytoplankton to UV-B radiation: oxidative stress and photoinhibition of photosynthesis are not prevented by UV-absorbing compounds in the dinoflagellate Prorocentrum micans

Lesser MP

Experiments on the temperate marine dinoflagellate Prorocentrum micans showed that cultures acclimated to moderate intensities (120 umol quanta m-2 s-1) of visible radiation and supplemental ultraviolet (UV) radiation exhibited significant inhibition of photosynthesis. This inhibition of photosynthesis caused a significant 30% decrease in specific growth rates for those cells exposed to UV radiation by the end of the 21 d culture. The mechanism for this decrease in chlorophyll specific photosynthetic rate does not appear to have been damage to photosystem II, as suggested for many acute exposure experiments. Rather, significant decreases in chlorophyll per cell and the specific activities of the carboxylating enzyme, Rubisco, explain the observed decrease in photosynthesis. The decrease in cellular chlorophyll and Rubisco activities occurs despite the presence and accumulation of mycosporine-like amino acids, whose UV absorbing properties have been suggested as an important protective mechanism against the deleterious effects of UV radiation. Our results also implicate oxidative stress, most likely a result of photodynamic interactions, as the cause for the decrease in Rubisco activities. Action spectra generated from these experiments show a significant decrease in the wavelength-dependent effects of UV radiation in cultures exposed to UV radiation, suggesting that UV-absorbing compounds do provide some, if not complete, protection. Previous predictions about specific changes in the shape of action spectra were centered around the absorption maximum of individual UV-absorbing compounds. The observed changes in the overall shape of the UV action spectra for photosynthesis in P. micans can be attributed to the broad overlapping absorption spectra of the suite of UV-absorbing compounds.

UV-B radiation . Oxidative stress . Photoinhibition . Phytoplankton . Photosynthesis

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