The event chain leading to germination blockage in durum wheat(Triticum turgidum ssp. durum Desf.) seeds exposed to the allelochemicalcoumarin (2H-chromen-2-one) was studied. The physiological and biochemicalaspects thought to be critical for a successful seed germination weremeasured. At concentrations above 200 2M, coumarin inhibited seedgermination in a concentration-dependent manner. Inhibition occurred earlyduring seed imbibition (phase I), was rapid, and irreversible. During phase I,coumarin inhibited water uptake, electrolyte retention capacity, and O2consumption. Later on, coumarin delayed the reactivation of peroxidases,enhanced the activity of superoxide dismutase, decreased the activities ofselected marker enzymes for metabolic resumption, and repressed thetranscription of molecular chaperons involved in secretory pathways.Insufficient and/or late seed rehydration caused by coumarin could havedelayed membrane stabilization or decreased respiratory O2 consumption,both of which are conducive to an overproduction of reactive O2 species.Being unbalanced by an adequate upsurge of antioxidant defense systems, theresulting oxidative stress might have ultimately interfered with the germinationprogram.
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