Factors controlling the formation of UV-absorbing mycosporine-like amino acids in the marine red alga Palmaria palmata from Spitsbergen (Norway)

The effects of various filtered natural radiation conditions (solar without UV-A+B, solar without UV-B, solar) on the contents of W-absorbing mycosporine-like amino acids (MAAs) in the marine red alga Palmaria palmata have been investigated in the Arctic Kongsfjord (Spitsbergen, Norway) over the summer 1997. Eight different W-absorbing mycosporine-like amino acids (MAAs) were detected in this alga, seven of which could be identified, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol and palythene. The remaining substance exhibited an absorption maximum at 357 nm, but could not be identified. The specific amount: of MAAs decreased with increasing collecting depth. Transplantation of P. palmata from 3 m depth to near surface water (0.2 m) followed by 1 week exposure to the various radiation treatments stimulated the accumulation of MAAs. All treatments led to a strong increase in total MAAs, but individual compounds showed different responses under the three spectral wavebands. While exposure to natural solar radiation without UV-A+B was accompanied with a. G-fold increase in the porphyra-334 concentration, treatment without W-B gave similar results plus an accumulation of shinorine. Under the full solar spectrum P. palmata showed the accumulation of three MAAs, porphyra-334 and shinorine, and additionally that of palythine. These data indicate a wavelength-specific stimulation of the formation of different MAAs, as well as the strongest accumulation of total MAAs under the full solar spectrum. In another experiment: P. palmata was collected from 7.5 m depth, transplanted to Im and exposed for 9 days to solar radiation without UV-A+B, solar radiation without UV-B and the full solar spectrum to follow the kinetics of MAA accumulation. All radiation treatments led to an accumulation of total MAA contents over time with the full solar spectrum being the most effective. However, in contrast to P. palmata transplanted from 3 m depth, plants from 7.5 m showed a different response in the MAA accumulation pattern. In the latter samples palythine was always the quantitatively dominant MAA and exhibited also the strongest increase after transplantation to shallow waters under all radiation treatments. Finally, a microscale variation in the MAA concentrations along the algal thalli was measured. Older self-shaded basal parts of P. palmata exhibited much lower MAA amounts than young apical tips. All data well support the suggested physiological function of MAAs as natural UV-sunscreens.