LAUSR

Several phytoplankton species produce the metabolites dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) but their intracellular roles need to be better understood. To improve the understanding of the DMSP antioxidant function suggested by Sunda et al. (2002), we exposed the diatom Skeletonema costatum, the Prymnesiophyceae Phaeocystis globosa and the dinoflagellate Heterocapsa triquetra to experimental treatments known to cause potential oxidative stress (high light intensities (HL); HL with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU); menadione sodium bisulfite (MSB)). DMSP and DMSO concentrations decreased after 6 h in all treatments indicating an interaction with Reactive Oxygen Species (ROS) produced. DMSP and DMSO-to-cell ratios in control conditions were higher for H. triquetra, while being unable to grow under HL. DMSP and DMSO-to-cell carbon were the highest for P. globosa, while the other species had similar values. During long-term treatment, these ratios were not increased in high-light grown cells of P. globosa and S. costatum. Overall, this illustrates that (1) the DMSP- and DMSO-to-cell or carbon seems to be not indicative of the capability of the species to tolerate an oxidative stress, (2) these molecules could react with ROS and lower their cellular concentration, but no clues demonstrated that these molecules are part of the antioxidant response of the cell.