Preservation protocol for dimethylsulfoniopropionate and dimethylsulfoxide analysis in plant material of the Mediterranean seagrass Posidonia oceanica, and re-evaluation of dimethylsulfoniopropionate leaf content

We tested three treatments to preserve Posidonia oceanica leaves for the analysis of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO): oven dried at 60 °C for 24 h, frozen at −20 °C, and frozen-in-ice and kept at −20 °C. The DMSP content was analyzed by proxy as dimethylsulfide (DMS) by gas chromatography after alkaline cleavage at room-temperature. The DMSP leaf content of P. oceanica in samples that were oven dried at 60 °C for 24 h, then stored at room temperature decreased by 87% over 80 days of storage and then remained stable for about 88 additional days compared to the control. The DMSO leaf content of P. oceanica in samples that were oven dried increased nine-fold after 198 days of storage following drying compared to the control. Both the DMSP and DMSO leaf content of P. oceanica remained stable for 198 days compared to the control with frozen and frozen-in-ice treatments, which we both recommend as adequate protocols to preserve P. oceanica tissues for DMS(P,O) analysis. The annual average DMSP leaf content of P. oceanica at 10 m in the Bay of Calvi (Corsica, France) was 205 ± 58 μmol g−1 (fresh weight) based on samples preserved frozen, two orders of magnitude higher than the value we previously reported based on samples that were oven dried. The newly determined DMSP leaf content allows ranking P. oceanica as the highest DMSP producer reported to date among marine and inter-tidal autotrophs.