Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1997
Publication Date: N/A
Citation: Ak, J., Gordon, W.R., Wagner, D., Quail, P.H., Poff, K.L. 1997. Multiple phytochromes are involved in red-light-induced enhancement of first-positive phototropism in Arabidopsis thaliana. Plant Physiology 113:975-979. Interpretive Summary: The amplitude of phototropic curvature to blue light is enhanced by prior exposure of seedlings to red light. This enhancement is mediated by phytochrome. Experimental results suggest that overexpression of either phyA or phyB perturbs the function of the endogenous photoreceptor system in an unpredictable fashion.
Technical Abstract: The amplitude of phototropic curvature to blue light is enhanced by a prior exposure of seedlings to red light. This enhancement is mediated by phytochrome. Fluence-response relationships have been constructed for red-light-induced enhancement in the phytochrome A (phyA) null mutant, the phytochrome B- (phyB) deficient mutant, and in two transgenic lines of Arabidopsis thaliana that overexpress either phyA or phyB. These fluence-response relationships demonstrate the existence of two responses in enhancement, a response in the very-low-to-low-fluence range, and a response in the high-fluence range. Only the response in the high-fluence range is present in the phyA null mutant. In contrast, the phyB-deficient mutant is indistinguishable from the wild-type parent in red-light responsiveness. These data indicate that phyA is necessary for the very-low-to-low but not the high-fluence response, and that phyB is not necessary for either response range. Based on these results, the high-fluence response, if controlled by a single phytochrome, must be controlled by a phytochrome other than phyA or phyB. Overexpression of phyA has a negative effect and overexpression of phyB has an enhancing effect in the high-fluence range. These results suggest that overexpression of either phytochrome perturbs the function of the endogenous photoreceptor system in an unpredictable fashion.