Dormancy of Medicago marina (L.) seed.

Medicago marina (L.) is a Mediterranean species whose seeds show strong dormancy that prevents germination. We used an integrated approach of physiological analyses and proteomics to investigate themechanisms that control M. marina dormancy/germination and that underlie stress tolerance. First, weevaluated the effects on dormancy breaking of the following treatments: mechanical scarification, freezing at −20◦C, storage for 4 months and heating at 100◦C for 1 h. Mechanical scarification and freezingwere the most effective treatments in overcoming dormancy. The role of abscisic acid (ABA) in M. marinadormancy was studied by ELISA immuno-enzymatic assay. The ABA content of germinated and nongerminated mature (control) and treated seeds was determined. The level of ABA was higher in treatedseeds than in control seeds; the most significant increase occurred in the heated seeds. A comparison ofthe ABA level in the germinated, control and treated seeds suggests that different mechanisms modulateABA content in response to different stresses, and that a specific ABA-signalling pathway regulates germination. Proteomic analysis revealed 46 proteins differentially expressed between treated and untreatedseeds; 14 of these proteins were subsequently identified by mass spectrometry. Several of the proteinsidentified are important factors in the stress response, and are involved in such diverse functions as lipidmetabolism, protein folding and chromatin protection. Lastly, an analysis of the phosphoproteome mapsshowed that the function of many proteins in seeds subjected to temperature treatment is modulatedthrough post-translational modifications.