Possible Involvement of the Alternative Respiration System in the Ethylene-stimulated Germination of Cocklebur Seeds

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RESUMO

Respiration of nondormant upper cocklebur (Xanthium pensylvanicum Wallr.) seeds was enhanced by exogenous C2H4, proportionally to the concentration of C2H4 and the duration of presoaking of the seeds. Benzohydroxamic acid (BHM) and salicylhydroxamic acid (SHM), inhibitors of alternative respiration, inhibited both the germination of nondormant lower cocklebur seeds and the respiration of the upper seeds presoaked for periods of 12 to 30 hours. Both the growth and respiration of axial and cotyledonary tissues were also inhibited by BHM. Moreover, BHM inhibited both the C2H4-induced germination of the upper seeds and their C2H4-stimulated respiration; the inhibition occurred only with concomitant addition of C2H4 and BHM. The respiration of seeds with a secondary dormancy induced by presoaking for prolonged periods was markedly stimulated by C2H4 but not suppressed by BHM. It was suggested that the alternative respiration system may be involved in the normal germination process of cocklebur seeds, secondary dormancy may result from its inactivation, and C2H4 may exert its germination-promoting action by stimulating the alternative respiration. The effects of BHM and SHM can suggest but not prove the involvement of the alternative respiration in seed germination.

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