UV radiation induced stress does not affect DMSP synthesis in the marine prymnesiophyte Emiliania huxleyi

Abstract

A possible coupling between UV radiation (UVR; 280 to 400 nm) induced stress and the production of dimethylsulfoniopropionate (DMSP), the precursor of the climate-regulating gas dimethylsulfide (DMS), was investigated in the marine prymnesiophyte Emiliania huxleyi. To this end, axenic cultures of E. huxleyi were exposed to a range of UVR doses for 2 consecutive days. During and after these treatments, growth, photosynthetic activity, cell size, DNA damage, sugar accumulation and DMSP concentrations were followed. The vulnerability of E. huxleyi for relatively low UVR doses was demonstrated by the inhibition of growth and the simultaneous occurrence of DNA damage. Also, mean cell size increased and sugars accumulated as a result of the UVR treat- ments. In contrast, no effect was observed on the optimal quantum yield of Photosystem II (PSII), a measure of the efficiency of photosynthesis. With increasing UVR dose, cellular DMSP content increased. However, the intracellular DMSP concentrations remained constant at the level typical for the applied temperature and salinity conditions, due to accompanying increase in cell size. The increased cellular DMSP content did not compensate, therefore, for the decreased growth rates, resulting in an overall decrease in the total amount of DMSP produced in the cultures. The UVR effects as induced in this study are assumed to be severe as compared with natural solar conditions, especially because high in situ UVAR (315 to 400 nm) may ameliorate UVBR damage by activation of photorepair. Yet the presented results imply that when (increased) UV(B)R causes growth rate reduc- tion of E. huxleyi in situ, DMSP fluxes are likely to be reduced too.