Freshly harvested seeds of the genetic line CS40 of wild oats (Avena fatuaL.) germinated in the dark. Brief (15ensp;min) exposure to far-red light after imbibition inhibited germination. Germination after a brief exposure to red light, as either a single or a terminal exposure, was higher than that after a brief far-red light irradiation, but lower than dark germination. After the hydrated seeds were irradiated for a prolonged period with far-red light and dried for 7 days, they germinated poorly and failed to respond to brief red light irradiation after rehydration. Forty days after drying, however, the far-red light pretreated seeds were induced to germinate and showed a typical phytochrome-mediated response. Prolonged far-red light irradiation inhibited the germination of halved, freshly harvested seeds only when the seeds were imbibed in polyethylene glycol solutions with considerable negative water potentials. The scutellum and radicle of a halved seed responded to the far-red light treatment differently, but correlatively. The unexpected inhibitory effects of brief red light irradiation on the freshly harvested seed are related to the specific physiological system in the seed.Key words: light, seed halves, water potential, phytochrome,Avena.
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