Plant Physiol, March 2003, Vol. 131, pp. 1411-1417
Phytochromes A and B Mediate Red-Light-Induced Positive
Phototropism in Roots1
John Z.
Kiss,2*
Jack L.
Mullen,2
Melanie J.
Correll, and
Roger
P.
Hangarter
Department of Botany, Miami University, Oxford, Ohio 45056 (J.Z.K.,
M.J.C.); and Department of Biology, Indiana University, Bloomington,
Indiana 47405 (J.L.M., R.P.H.)
The interaction of tropisms is important in determining the final
growth form of the plant body. In roots, gravitropism is the
predominant tropistic response, but phototropism also plays a role in
the oriented growth of roots in flowering plants. In blue or white
light, roots exhibit negative phototropism that is mediated by the
phototropin family of photoreceptors. In contrast, red light induces a
positive phototropism in Arabidopsis roots. Because this
red-light-induced response is weak relative to both gravitropism and
negative phototropism, we used a novel device to study phototropism
without the complications of a counteracting gravitational stimulus.
This device is based on a computer-controlled system using real-time
image analysis of root growth and a feedback-regulated rotatable stage.
Our data show that this system is useful to study root phototropism in
response to red light, because in wild-type roots, the maximal
curvature detected with this apparatus is 30° to 40°, compared with
5° to 10° without the feedback system. In positive root
phototropism, sensing of red light occurs in the root itself and is not
dependent on shoot-derived signals resulting from light perception.
Phytochrome (Phy)A and
phyB were severely impaired in red-light-induced
phototropism, whereas the phyD and phyE
mutants were normal in this response. Thus, PHYA and PHYB play a key
role in mediating red-light-dependent positive phototropism in roots.
Although phytochrome has been shown to mediate phototropism in some
lower plant groups, this is one of the few reports indicating a
phytochrome-dependent phototropism in flowering plants.
1
This work was supported by the National
Aeronautics and Space Administration (grant no. NCC2-1200).
2
These authors contributed equally to the paper.
*
Corresponding author; e-mail kissjz{at}muohio.edu; fax
513-529-4243.
© 2003 American Society of Plant Biologists
