Photoreversibility of Leaf and Hypocotyl Elongation of Dark Grown Red Kidney Bean Seedlings

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Abstract
Dark Red Kidney bean seedlings were grown for 10 days in complete darkness, except for brief exposures to radiant energy on the sixth, seventh, and eighth days, and were harvested on the tenth day after planting. Light acts on the dark-grown seedlings to promote leaf expansion and to inhibit hypocotyl elongation; the action spectrum having a maximum in the red near 6500 A. Seedlings that are irradiated with red can be prevented almost completely from responding by a subsequent irradiation with far red. The action spectrum for this response has its maximum near 7300 A. These two action spectra are respectively the same as those for promotion and inhibition of germination of light-sensitive seed and for inhibition and repromotion of flowering of short-day plants. Repeated alternations of red and far red result in essentially no diminution of responsiveness, the final effect depending upon the type of radiation last received. Duration of time between the red and far-red irradiation treatments has only a small effect on the far-red response, even when several hours are interposed.