Unveiling the Role of DMSO in Seagrass Physiology: A Focus on Posidonia oceanica

Dimethyl sulfoxide (DMSO), produced by various phytoplankton species and macrophytes, is the most abundant biogenic sulfur compounds in the marine environment. It is derived from the oxidation of dimethylsulfide (DMS), a key compound in the marine sulfur cycle and contributing to global climate regulation. Despite its relevance, the specific natural functions of DMSO for producer organisms remain largely unknown. This study investigated the hormetic response of increasing exogenous DMSO concentrations to decipher its role in the marine plant Posidonia oceanica, a keystone species in Mediterranean marine biodiversity and major producer of DMSO. Treatment with 1% DMSO significantly increased elongation of adult (204%) and intermediate (46%) leaves, number of juvenile leaves and boosted chlorophyll a (50%) and b (65%) concentration. Concentrations above or below this threshold had negative effects; specifically, 0.1% DMSO had a negative impact on intermediate leaves elongation (29% decrease) and on chlorophyll b (45% decrease). Proteomic analysis showed that DMSO inhibits primary metabolism while activating secondary metabolic pathways. Photosynthesis, glycolysis, translation were depleted, while vacuolar metabolism enhanced. To cope energy for growth and tolerate the stress, under 1% DMSO concentration the flavonoid biosynthesis was hugely enhanced. Significant accumulation of proteins involved in the glutamine synthesis, assured the nitrogen source for plant growth and development. These findings suggest DMSO modulates leaf meristem activity, regulates cellular osmosis, and protects against oxidative damage. Future work should investigate the molecular mechanisms behind these roles and explore the broader ecological impact of DMSO on marine sulfur cycling and P. oceanica interactions. Graphical Abstract: (Figure presented.)