Persistence of Red Light Induction in Lettuce Seeds of Varying Hydration 1

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Incubation of lettuce seeds (Lactuca sativa L. cv. Grand Rapids) in 0.3 m mannitol allows sufficient water uptake to make seeds fully sensitive to red light. But germination is possible only after lowering the osmotic potential of the incubation medium. The red light induction of these incompletely hydrated seeds can be reversed by far red light. Their reversibility declines with time at a slower rate than seeds incubated in water. About half the seeds in 0.3 m mannitol respond to far red light when all seeds in water have escaped control by far red light. Close to 100% of the seeds remain sensitive to far red exposure if 0.6 m mannitol is used as osmoticum. The retention of the original red light stimulus is inversely related to the concentration of the incubation medium.

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