Action of ferric and aluminium ions on the dormancy breakage of Stylosanthes humilis seeds

Dormancy of scarified seeds of Stylosanthes humilis was broken by acidic Al 3+ and Fe 3+ solutions. Fe +3 -stimulated seeds exhibited a high activity of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and produced great amounts of ethylene, which showed correlated with the germination process. In addition, specific inhibitors of ethylene biosynthesis and action largely depressed the Fe 3+ -stimulated germination, leading to the conclusion that the ion broke dormancy by triggering ethylene production by the seeds. By contrast, inhibitors of ethylene biosynthesis and action did not impair germination of Al 3+ -stimulated dormant seeds. Moreover, ethylene production and activity of ACC oxidase of Al 3+ -treated seeds was substantially decreased by inhibitors of ethylene biosynthesis, but germination kept large. Together these data suggest that ethylene biosynthesis was not required in the chain of events triggered by Al 3+ leading to dormancy breakage. Methyl viologen (MV), a reactive oxygen species-generating compound, broke dormancy of seeds to the same extent as Al 3+ did. Germination of both Al 3+ - and MV-stimulated dormant seeds was inhibited by sodium selenate, an antioxidant compound; selenate, however had no effect on germination of Fe 3+ -stimulated seeds. Together these data indicate that the mechanisms underlying the germination of Al 3+ - and Fe 3+ -treated seeds are not the same.