Dimethyl sulfoniopropionate and dimethyl sulfide production in response to photoinhibition in Emiliania huxleyi

Abstract

The response in intracellular dimethyl sulfoniopropionate (DMSP) and dissolved DMSP and dimethyl sulfide (DMS) concentrations when Emiliania huxleyi was exposed to acute (1‐h) increases in photon flux densities of photosynthetically active radiation (PAR) and ultraviolet (UV) radiation was examined in cells acclimated to low light (LL, 30 µmol photons m−2 s−1) and high light (HL, 300 vmol photons m−2 s−1). LL‐acclimated cells displayed greater photoinhibition, assessed as a decrease in maximum photochemical efficiency (Fv : Fm). Photoinhibition was increased by exposure to UV wavelengths. LL‐acclimated cells also exhibited more light dissipation through the xanthophyll cycle, evident as changes in de‐epoxidation state. Greater photoinhibition in LL‐acclimated cells corresponded with increased accumulation of DMSP of 21% ± 4% relative to initial concentrations, contrasting with a slight decrease of 5% ± 6% in HL‐acclimated cells. Exposure to UV appeared to decrease the rates of intracellular accumulation of DMSP. Conversely, PAR + UV exposure stimulated the net production of dissolved DMSP and DMS in both HL‐acclimated and LL‐acclimated cultures, compared with high PAR alone. The results indicate a direct link between acute photo‐oxidative stress and DMSP synthesis by E. huxleyi. The physiological basis for increased release of DMSP and DMS from cells due to high PAR + UV exposure is unclear. However, the timescales of changes in intracellular DMSP, dissolved DMSP, and DMS are consistent with variations in light intensity experienced by phytoplankton in a turbulent mixed layer and are similar to rates of change in photosynthetic parameters associated with photoacclimation.