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Dose-Response Curves for Radish Seedling Phototropism ^1,2

^a Division of Biological and Medical Research, Argonne National Laboratory, Argonne, Illinois 60439

Radish seedlings (Raphanus sativus L.) were grown for 4 days in complete darkness, or in white light, or for 3 days in darkness followed by 1 day of red light. Phototropic dose-response curves for the seedlings grown in these three ways were determined with 460-nm light. The dark-grown and red light-treated seedlings responded with positive curvatures of no more than 10° to energy doses in the first positive range and with larger positive curvatures in the second positive dose range. No indifferent or negative curvature was seen with the light intensity used. White light-grown seedlings did not respond to first positive energy doses, but responded as strongly to second positive doses as the other types of seedlings.

¹ Research was supported by the Faculty Research Participation Program under the auspices of the United States Atomic Energy Commission.

² This paper is dedicated to the late Solon A. Gordon, to whom I am grateful for his interest in this work and in whose laboratory this work was done.