UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350 700 nm). UV absorption was high; chlorophyll-specific absorption, a*(ph), at 330 nm ranged from 0.06 to 0.41 m(2)/mg chlolophyll a. Values of a*(ph) (330) were 4-13 times greater than a*(ph) (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine al-e responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll rr or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher il radiances. The relative fluorescence yield for chlorophyll Lr was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll ii in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light.