Accumulation Of Mycosporine-like Amino Acids Research Articles

Dietary accumulation of UV-absorbing mycosporine-like amino acids (MAAs) by the green sea urchin (Strongylocentrotus droebachiensis)

The bioaccumulation of ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs) by Strongylocentrotus droebachiensis (Muller) was determined in specimens maintained on MAA-rich and MAA-deficient diets. Individuals were fed either the red alga Mastocarpus stellatus (Stackhouse), which has a high concentration of the MAA shinorine (6.98 nmolmg−1 dry wt), and trace amounts of the MAAs porphyra-334, asterina-330 and palythine, or the brown alga Laminaria saccharina (Lamouroux), which contains no detectable MAAs. Reproductively spent urchins were fed ad libitum during a 9 mo period in 1992 to 1993 until they were once again gravid. To monitor accumulation, samples of urchin tissues and ingested food were taken throughout the 9 mo period from males and females maintained on each diet, and the concentrations of MAAs determined using high performance liquid chromatography. Urchins maintained on a diet of M. stellatus showed an ovarian shinorine concentration (8.33 nmol mg−1 dry wt) 25 times higher than those fed L. saccharina. There was no change in MAA content of testes or somatic tissues in either feeding group. More than 99% of the MAAs present in an experimental meal of M. stellatus were removed during passage through the gut. Previous studies have inferred dietary accumulation of MAAs by comparing MAAs present in animal tissues with the consumer's potential diet in the field. This is the first study to have monitored MAA accumulation in animal tissues in conjunction with a controlled diet having a known MAA composition. Concentrating MAAs in the ovaries may provide eggs released into the water column with protection from damaging solar ultraviolet radiation.

Evidence Regarding the UV Sunscreen Role of a Mycosporine-Like Compound in the Cyanobacterium Gloeocapsa sp

The UV sunscreen role commonly ascribed to mycosporine-like amino acids (MAAs) was investigated with an isolate of the terrestrial cyanobacterium Gloeocapsa sp. strain C-90-Cal-G.(2), which accumulates intracellularly an MAA with absorbance maximum at 326 nm but produces no extracellular sunscreen compound (i.e., scytonemin). The intracellular concentrations of MAA achieved were directly related to the intensity of the UV radiation (maximum at 320 nm) received by the cells. However, the presence of high concentrations of MAA was not necessary for the physiological acclimation of the cultures to UV radiation. The measured sunscreen factor due to MAA in single cells was 0.3 (the MAA prevented 3 out of 10 photons from hitting potential cytoplasmic targets). High contents of MAA in the cells correlated with increased resistance to UV radiation. However, when resistance was gauged under conditions of desiccation, with inoperative physiological photoprotective and repair mechanisms, cells with high MAA specific contents were only 20 to 25% more resistant. Although UV radiation centered around both 320 and 365 nm resulted in chlorophyll a photobleaching and photoinhibition of photosynthesis, the difference in sensitivity correlated with MAA accumulation occurred only at 320 nm (absorbed by MAA) and not at 365 nm (not absorbed by MAA). This difference represents the maximal protection ascribable to the presence of MAA for single cells, i.e., if one does not consider the enhancing effects of colony formation on protection by sunscreens.