Series temporales de medida de radiación solar ultravioleta y fotosintética en Málaga / Time series of ultraviolet and photosynthetic solar radiation measurements in Málaga

Introducción: La radiación ultravioleta es el principal factor etiopatogénico de las formas más frecuentes del cáncer de piel. En la provincia de Málaga es habitual la exposición solar continuada, sobre todo por tener una alta afluencia de turismo y, además, por ser una región donde se desarrollan gran número de actividades actínicas, tanto laborales como de ocio. Material y métodos: Se determinan series temporales de medida de radiación ultravioleta UVB, UVA y radiación fotosintéticamente activa (PAR) solar en Málaga (36,5° N-4,7° O) utilizando la recién constituida Red de Medida de Radiación Ultravioleta-Fotosintética de Andalucía (UVIFAN) (http://uvifan.scai.uma.es). Resultados: Se presentan ciclos anuales desde el año 1997 hasta finales de 2001 de la dosis diaria total para las tres bandas de radiación. Las dosis diarias máximas se observan en los meses estivales. El índice UV, que se alcanza en las horas centrales del día, osciló entre valores máximos de 7-8 durante los meses estivales y valores de 1-2 en los meses de invierno. Las relaciones de dosis PAR/UVA no varían a lo largo del año, aunque la relación UVB/UVA y UVB/PAR sigue un patrón anual de variación con valores máximos en los meses estivales, mientras que los valores más bajos se obtuvieron durante los meses invernales. Conclusiones: Estos datos confirman que en la provincia de Málaga, en los meses estivales existen niveles muy altos de radiación UVA, UVB y PAR, por lo que es de suma importancia adoptar medidas específicas de fotoprotección en esta época para evitar tanto las quemaduras a corto plazo, como la fotocarcinogénesis y el fotoenvejecimiento a largo plazo (AU)

Tissular localization of coumarins in the green alga Dasycladus vermicularis (Scopoli) Krasser: a photoprotective role?

Cell distribution of coumarins, a group of UV-absorbing substances, was analysed by epifluorescence optical microscopy in the green macroalga Dasycladus vermicularis. Maximal concentration of 3,6,7-trihydroxycoumarin (THC), which corresponds to almost 100% of the total coumarins in D. vermicularis, was found in the apical part of the thallus, which is more exposed to solar radiation. At a cell level, two blue, highly fluorescent layers, corresponding to a large accumulation of THC, were found in the internal part of the cell wall and around the vacuolar membrane. The percentage of UV radiation absorbed by each THC layer could be measured from the in vitro total thallus concentration of THC and histological measurements of the layers. The THC layer close to the cell wall absorbed 88% of the incident irradiance at 346 nm (corresponding to the maximum of absorbance of THC in the UVA region), while that close to the vacuole membrane absorbed 87.5%. These results agree with the hypothesis of a natural sunscreen role, significantly reducing harmful UV radiation reaching the cell. Owing to the release of this substance into the medium under different stress conditions, its capacity as a UV filter for other macroalgae has been tested. The ecological relevance of the release process of this UV-absorbing substance in specific environments is discussed.

Effects of short-term irradiation on photoinhibition and accumulation of mycosporine-like amino acids in sun and shade species of the red algal genus Porphyra.

The effect of irradiance (40 and 840 micromol photons m(-2) s(-1)) of short-term (48 h) irradiation on photosynthetic activity (estimated as oxygen evolution and as chlorophyll fluorescence), specific absorption and fluorescence excitation spectra, photosynthetic pigment accumulation (chlorophyll a and biliproteins) and UV-absorbing compounds (mycosporine-like amino acids, MAAs) was investigated in sun and shade species of the red algal genus Porphyra collected in Trondheimsfjord (Norway). In the sun type, high irradiance exposure (840 micromol photons m(-2) s(-1)) did not alter the Chl a concentration, however, exposure to a lower irradiance (40 micromol photons m(-2) s(-1)) for 48 h significantly increased the chlorophyll concentration. The content of MAAs was significantly higher in the suntype than in the shade type algae. Porphyra-334 is the main MAA in this species followed by shinorine. The total content of MAAs significantly (P<0.05) increased in the sun type after 48 h exposure to both high and low irradiances. However, in the shade type, porphyra-334 significantly decreased (P<0.05) after both high and low irradiance exposure. Photosynthetic activity (as oxygen evolution) and the optimal quantum yield (F(v)/F(m)), as an indicator of photoinhibition, decreased under low and high irradiance in the shade type algae and no full recovery was observed when the algae were transferred to very low irradiation. The sun type algae presented a higher capacity of acclimation to increased irradiance than the shade type algae. This high acclimation of sun type algae to short term high irradiance exposure (48 h) is explained by the higher thermal dissipation. This was estimated as the ratio of nonphotochemical quenching related to the light dose (q(N):dose) and by the accumulation of MAAs.