Effect of UV radiation on growth, chlorophyll fluorescence and fatty acid composition of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae)

Abstract

Y. Liang, J. Beardall and P. Heraud. 2006. Effect of UV radiation on growth, chlorophyll fluorescence and fatty acid composition of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae). Phycologia 45: 605–615. DOI: 10.2216/04-61.1

The effect of UV radiation on growth, the maximal effective quantum yield of photosystem II (F_v/F_m), the photosynthetic parameters α, ETR_max and I_k, and the fatty acid composition of two diatoms, Phaeodactylum tricornutum and Chaetoceros muelleri, were examined in batch cultures. The cultures were grown at 18 ± 1°C with a 16 : 8 light : dark cycle under three different light regimes: photosynthetically active radiation (PAR) only (60 μmol photons · m⁻² · s⁻¹); PAR + UVA radiation (UVAR) [PAR (60μmol photons · m⁻² · s⁻¹) plus 8.22 Wm⁻² UVAR] and PAR + UVAR + UVB radiation (UVBR) [PAR (60 μmol photons · m⁻² · s⁻¹) plus 13.73 Wm⁻² UVAR plus 1.04 Wm⁻² UVBR]. The cell density, the F_v/F_m and α values of P. tricornutum and C. muelleri were all inhibited as a consequence of PAR + UVAR + UVBR exposure during the experimental period; on the other hand, ETR_max and I_k were somewhat enhanced under this exposure regime. The P. tricornutum samples were harvested at midexponential growth phase while C. muelleri samples were withdrawn on Days 6, 8 and 10 for fatty acid analysis. UV radiation induced significant differences in all the major fatty acids of P. tricornutum. The percentages of eicosapentaenoic acid (EPA) and polyunsaturated fatty acids (PUFA) increased while monounsaturated fatty acids (MUFA) decreased in the PAR + UVAR treatment in comparison with the PAR-only and PAR + UVAR + UVBR treatments. On the other hand, all the major fatty acids of C. muelleri varied with harvest stage and UVR. The percentages of MUFA in C. muelleri increased, while EPA and PUFA decreased under PAR + UVAR + UVBR treatment. Our results indicated that PAR + UVAR may promote EPA and PUFA formation in P. tricornutum, whereas PAR + UVAR + UVBR enhanced SFA and MUFA, and suppressed PUFA formation in C. muelleri.

Key Words::

• Chaetoceros muelleri
• Chlorophyll fluorescence
• Fatty acids
• Phaeodactylum tricornutum
• UV radiation

ACKNOWLEDGMENTS

This work was supported in part by the Australian Research Council. We also thank the China Scholarship Council (CSC) for provided the opportunity for the first author to visit and carry out these experiments in Australia.