Light Actions in the Germination of Cocklebur Seeds

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Abstract
Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actions in the germination of cocklebur seeds. IV. Disappearance of red light-requirement for the germination of upper seeds subject to anoxia, chilling, cyanide or azide pretreatmenL—J. exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic upper cocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreating with anoxia, chilling, cyanide or azide, which stimulates their dark germination, were examined in relation to light actions. Prior to experiments, seeds were pre-soaked at 23 °C in the dark for 1 or 2 weeks to remove the pre-existing Pfr. When the prctreatment conditions were suboptimal for germination induction, the stimulating effects of the pretreatments on germination during a subsequent dark period at 23 °C were manifest only when seeds were irradiated with red light before or after the pretreatment Red light promotion was reversed by blue or far-red light treatment. However, both prc-chilling for 6 d at 8 °C and prctreatment with 1· 5 mol m − 3 NaN3 for 2 d could induce full germination without red light exposure. On the other hand, both pre-exposure to anoxia for 8 d and pretreatment with 30 mol m−3 KCN could induce the dark germination only when germination occurred at 33 °C which is known to augment the ratio of an alternative respiration flux to a cytochrome one. Moreover, the dark germination in response to these inductions were strongly inhibited by the inhibitors of alternative respiration, propyl gallate and benzohydroxamic acid, applied during a subsequent dark period. It was thus suggested that Pfr has some relation to the operation of two respiration systems of cocklebur seeds, but it is not indispensable to germination of this positively photoblastic seed.