On a Blue Light Effect and Phytochrome in the Stimulation of Georesponsiveness of Maize Roots

Abstract

Summary Maximal stimulation of the geotropic response of maize roots (Badischer Landmais) occurs in red and blue light. A plateau and two peaks at 455 and 484 nm in the blue region and a broad maximum extending from the yellow to the dark red region can be distinguished if the light dose is low (1.3 to 2.6 nE/CM 2 ) and applied during a short period of time. The geostimulation by light can largely be reverted by far red light given after a stimulus. There is no doubt that phytochrome is involvedbut the spectral response curve points toward the participation of additional photoreceptors e.g. the blue light photoreceptor. Responses occuring in yellow light cannot easily be traced back to a known photoreceptor. In the light of existing hypotheses about geotropism and the action and location of morphogenetically active photoreceptors wthe results may best be interpreted by the assumtion that light-stimulated changes in membran permeability may allow a better flow of growth inhibiting substances coming from the root cap.