Light Actions in the Germination of Cocklebur Seeds II. Possible Origin of the Diversity of Light Responses in Seed Germination

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In negatively photoblastic, lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.), the respective germination-inhibiting effects of red (R) and far-red (FR) lights were found in the proximal and near-tip zones of the axial tissues. In contrast, the germination-stimulating effect of R in positively photoblastic, upper cocklebur seeds was manifested in the near-tip zone of the axes, the R effect being reversed when FR was given to the zone. The R-sensitive zone in the upper seeds, however, shifted towards the more proximal zone as the period of pre-soaking at low temperatures increased. This shift was accompanied by the ability to germinate in the dark in the upper seeds. In the lower seeds, R inhibited axial growth in the near-tip zone, whereas FR inhibited it in the proximal zone. In contrast, axial growth in the near-tip zone of the upper seeds was promoted by R. In both seeds, light had little effect on the growth of the radicle tip. Pre-soaking at low temperatures induced dark-germination by hastening the axial growth of the upper seeds, thus allowing the upper seed to resemble the lower one. We therefore propose a hypothesis that explains the diversification of photoresponses in seed germination.
日本植物生理学会の論文