Overview of UV-absorbing Pigments in Marine Algae

Algae > Volume 14(3); 1999 > Article

Algae 1999;14(3): 201-212.

Jin-Hee Park, Taejun Han

Engineering Center, Dongseo University. Department of Biology, University of Inchon

ABSTRACT

The stratospheric ozone depletion due to anthropogenic activities has resulted in increasing flux of solar midultraviolet radiation (UV-B; 280-320 nm) to the earth's surface and to ecologically significant depth in the ocean. Rising UV-B levels are potentially threatening organisms since UV-radiation is readily absorbed by some important biomolecules such as DNA, protein and lipids. There has been extensive documentation of adverse effects of UV-B on marine algae, which include increase in mortality, reduction in growth and photosynthetic rates, inhibition of carbon and nitrogen assimilation, destruction of photosynthetic pigments and retardation of reproductive cell motility and so on. There are adaptive ways by which UV-induced damage is mitigated. One of the mechanisms is the presence of UV-absorbing pigments (UVP). Compounds of these types have now been isolated from various marine organisms and identified as a series of mycosporine-like amino acids (MAAs). The MAAs are composed of a cyclohexenone ring attached with an amino acid side group. These compounds absorb in wavelengths ranging from 310 to 365 nm, spanning both UV-B and UV-A (320-400nm) portions of the solar spectrum, but transmit photosynthetically active radiation (PAR; 400-700nm), Seven MAAs have so far been isolated from marine macroalgae and identified as mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol, usujirene and palythene. The role of MAAs as UV protectants is inferred from observations that their concentrations are correlated with the environmental UV fluences organisms can experience. Antarctic rhodophytes with high concentrations of UVP were more tolerant of natural and artificial UV than those with lower concentrations. However, the link between UVP levels and UV-B sensitivity is not always straightforward. In addition, the main absorption band of MAAs is well in the UV-A, thus making it difficult to assume the protective role of minimizing UV-B damage. For example, methanol extracts of two Korean macrophytes, namely Ulva pertusa (Chlorophyta) and Kjellmaniella crassifolia (Phaeophyta) have shown strong absorption characteristics with the former at 300 nm and the latter at 340 nm. The UV-B sensitivity was however significantly different with the green alga being much less sensitive than the brown alga. There is also experimental evidence that MAAs formation is regulated not only by UV but by PAR. Although biochemical detection and characterization of MAAs have been well established with a variety of macroalgae the physiological and ecological function of the compounds is yet largely unknown, The potential of MAAs as UV protectants remains to be determined by sustained and comprehensive studies of the compounds.

Key words: MAAs, Ozone depletion, UV-B, UV-absorbing pigments, UV-protectants