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BARBIERI Elena Susana

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Título:

Evolution of chlorophyll-a and UV-absorbing compounds in the dinoflagellate Heterocapsa triquetra when exposed to ultraviolet radiation.

Autor/es:

BARBIERI, E.S.; VILLAFAÑE, V.E.; HELBLING, E.W.

Lugar:

Vigo, España

Reunión:

Simposio; II Plankton Symposium; 2003

Resumen:

The aim of this study was to evaluate the evolution of chlorophyll-a (chl-a) and UV-absorbing compounds in the dinoflagellate Heterocapsa triquetra (Ehrenberg) Stein when exposed to different artificial radiation conditions. Samples were incubated in an illuminated chamber under irradiances of 66 W m-2 for PAR (400-700 nm), 15.3 W m-2 for UV-A (315-400 nm) and 0.7 W m-2 for UV-B (280-315 nm) in six 500 ml- Plexiglas UV transparent containers under three radiation treatments: a) two uncovered containers which received all radiation (PAR + UV-A+ UV-B); b) two containers covered with a filter (cut - off at 320 nm, Montagefolie, Folex, Dreieich, Germany) which received PAR + UV-A and, c) two containers covered with Ultraphan -395 UV Opak film (50% transmission at 395 nm) which received only PAR. During the first seven days, one sample from each radiation treatment was incubated under 100 % irradiance whereas the remaining three samples were incubated at 25 % of this total radiation. Then, those samples receiving 100% of the irradiance were put at 25 % and vice versa (i.e., cells under 25 % irradiance were put at 100%) for five more days. H. triquetra had a short lag face (i.e., two days) for all treatments, except those under PAR + UV-R, where this period lasted three days. The highest specific growth rate (µ) values were determined under PAR (i.e., µ = 0.67 and µ = 0.69 for 100% and 25 % respectively), whereas the lowest (i.e., µ = 0.57 and µ = 0.62 for 100% and 25 % respectively) were measured under PAR + UV-R treatments; however, there were no significant (p > 0.05) differences between treatments. At the beginning of the experiment, cells had relatively low concentrations of UV-absorbing compounds, which increased exponentially for the next five days. The ratio of UV-absorbing compounds (peak at 334 nm) to chl-a (peak height at 666 nm) varied between those cells exposed to PAR + UV-R and PAR only (p < 0.05), being maximal under PAR when cells were exposed to high irradiances. After samples being inverted (i.e., in regard to radiation intensity, day 8), the concentration of UV-absorbing compounds per cell increased in all treatments, especially in samples receiving 100 % irradiance after day 8 but finally, this concentration decreased. In general, it was determined that the ratio 334 nm / 666 nm was more influenced by the quantity than by the quality of radiation received by the cells. Our results show that, based on the dynamics of synthesis of chl-a and UV-absorbing compounds, H. triquetra can be considered a species relatively resistant to UVR.

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