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 mycospor ine-like amino acids (MAAs) in the marine red alga Palmaria palmata have be en investigated in the Arctic Kongsfjord (Spitsbergen, Norway) over the sum mer 1997. Eight different W-absorbing mycosporine-like amino acids (MAAs) w ere detected in this alga, seven of which could be identified, namely mycos porine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythino l and palythene. The remaining substance exhibited an absorption maximum at 357 nm, but could not be identified. The specific amount: of MAAs decrease d 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 vari ous radiation treatments stimulated the accumulation of MAAs. All treatment s led to a strong increase in total MAAs, but individual compounds showed d ifferent responses under the three spectral wavebands. While exposure to na tural solar radiation without UV-A+B was accompanied with a. G-fold increas e in the porphyra-334 concentration, treatment without W-B gave similar res ults plus an accumulation of shinorine. Under the full solar spectrum P. pa lmata showed the accumulation of three MAAs, porphyra-334 and shinorine, an d additionally that of palythine. These data indicate a wavelength-specific stimulation of the formation of different MAAs, as well as the strongest a ccumulation of total MAAs under the full solar spectrum. In another experim ent: P. palmata was collected from 7.5 m depth, transplanted to Im and expo sed for 9 days to solar radiation without UV-A+B, solar radiation without U V-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 co ntrast 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 th e strongest increase after transplantation to shallow waters under all radi ation treatments. Finally, a microscale variation in the MAA concentrations along the algal thalli was measured. Older self-shaded basal parts of P. p almata exhibited much lower MAA amounts than young apical tips. All data we ll support the suggested physiological function of MAAs as natural UV-sunsc reens.