Multiple phytochromes are involved in red-light-induced enhancement of first-positive phototropism in Arabidopsis thaliana.
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 Rabidopsis thaliana that overexpress either phyA or phyB. These fluence-response relationships demonstrate the existence of two response 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 indiacate that phyA is necessary for the very-low-to-low but not the high-influence 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 aphytochorme other than phyA of 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.
Janoudi
A K
AK
Michigan State University, Department of Energy Plant Research Laboratory, East Lansing 48824, USA.
Gordon
W R
WR
Wagner
D
D
Quail
P
P
Poff
K L
KL
D017360:Arabidopsis / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D008969:Molecular Sequence Data; D018524:Phototropism; D010834:Phytochrome / Q000378:metabolism*; D030821:Plants, Genetically Modified
D010834:Phytochrome