Study of seed priming mechanisms of three plant species used in revegetation of industrial sites

Efficient seed germination and seedling growth are frequently compromised during revegetation of former industrial sites. In this thesis, we investigated whether seed priming can improve revegetation strategies. The objectives were (1) to understand seed priming effect on germination, seedling emergence, growth and ion uptake and (2) to analyse the priming-induced mechanisms in seeds. Priming with polyethylene glycol (PEG), gibberellic acid (GA3) and water was first assessed in Petri dishes and improved germination speed in Festuca rubra (+10%) and Trifolium repens (+50%) and in addition, the final germination rate in Poa pratensis (+25%). In these species, it was observed that seed imbibition occurred faster for primed seeds than for control seeds. It was suggested that circular depressions on the seed coat, in addition to tissue detachment inside the seed could be linked to the higher rate of imbibition in T. repens but not in the grass species. The advantage of priming was not related to the advancement of the cell cycle as clearly demonstrated by flux cytometry analysis but correlated well with protein mobilisation and higher á- and â-amylase activities in P. pratensis. In this species, protein abundance of glutenin LMW á-gliadin and one isoform of ã-gliadin precursor decreased significantly after priming while â-amylase abundance significantly increased after priming. These observations suggest an activation of starch and seed storage protein metabolism during priming as revealed by two-dimensional difference in-gel electrophoresis (2D-DiGE) proteomic technique. The effect of priming was secondly examined in soils differing in their fertility level and heavy-metal (HM) content. Priming improved seedling emergence and early growth of Poa pratensis but did not affect nutrient composition and metal content. In contrast, it increased Cd and Pb content in Trifolium repens. Finally, influence of priming, sowing rate and liming were analysed in situ and using hydroseeding technique on a sterile tailing (Antoing) and a tailing characterised by low fertility and HM contamination (Seilles). Seed priming had a positive impact on vegetation cover (+6%) in Seilles site only.Doctorat en sciences agronomiques et ingénierie biologique (AGRO 3)--UCL, 200