The effect of visible light stress on chemical signaling in two life stages of Emiliania huxleyi

The cosmopolitan marine phytoplankton species Emiliania huxleyi presents a digenetic heteromorphic life cycle, with the non-motile diploid phase bearing coccoliths and the flagellated haploid phase being non-calcified. E. huxleyi contains high concentrations of dimethylsulphoniopropionate (DMSP), the precursor of dimethylsulphide (DMS). DMSP is a multifactorial compound; it acts as a compatible solute in cell metabolism and as a chemical signal influencing bacterial and protist behavior. In the atmosphere DMS enhances cloud formation influencing climate. However, little has been documented on E. huxleyi chemical signal responses to high light stress, and how this relates to the heteromorphic life cycle. To this end, low light acclimated cultures of both haploid and diploid E. huxleyi were exposed to high light for 2 hr and allowed to recover in low light for 2 hr. During and after these treatments, growth, photosynthetic efficiency (Fv/Fm), DMSP (intracellular and released) and cell chlorophyll content were measured. Our preliminary results suggest that presence of high light decreased Fv/Fm to a greater extent in haploid than in diploid (calcified) cells, while recovery of Fv/Fm was rapid in both life stages. The chlorophyll content and intracellular DMSP was not different in both life stages. However, the dissolved DMSP increased after light stress in diploid cells suggesting a possible advantage as antioxidant protection or another cellular function, such as grazing protection in this life stage.