First published online February 17, 2006; 10.1104/pp.105.075671
Plant Physiology 140:1384-1396 (2006)
© 2006 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
Ethylene Modulates Flavonoid Accumulation and Gravitropic Responses in Roots of Arabidopsis1,[W]
Charles S. Buer2,
Poornima Sukumar and
Gloria K. Muday*
Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109
Plant organs change their growth direction in response to reorientation relative to the gravity vector. We explored the role of ethylene in Arabidopsis (Arabidopsis thaliana) root gravitropism. Treatment of wild-type Columbia seedlings with the ethylene precursor 1-aminocyclopropane carboxylic acid (ACC) reduced root elongation and gravitropic curvature. The ethylene-insensitive mutants ein2-5 and etr1-3 had wild-type root gravity responses, but lacked the growth and gravity inhibition by ACC found in the wild type. We examined the effect of ACC on tt4(2YY6) seedlings, which have a null mutation in the gene encoding chalcone synthase, the first enzyme in flavonoid synthesis. The tt4(2YY6) mutant makes no flavonoids, has elevated indole-3-acetic acid transport, and exhibits a delayed gravity response. Roots of tt4(2YY6), the backcrossed line tt4-2, and two other tt4 alleles had wild-type sensitivity to growth inhibition by ACC, whereas the root gravitropic curvature of these tt4 alleles was much less inhibited by ACC than wild-type roots, suggesting that ACC may reduce gravitropic curvature by altering flavonoid synthesis. ACC treatment induced flavonoid accumulation in root tips, as judged by a dye that becomes fluorescent upon binding flavonoids in wild type, but not in ein2-5 and etr1-3. ACC also prevented a transient peak in flavonoid synthesis in response to gravity. Together, these experiments suggest that elevated ethylene levels negatively regulate root gravitropism, using EIN2- and ETR1-dependent pathways, and that ACC inhibition of gravity response occurs through altering flavonoid synthesis.
1 This work was supported by the National Aeronautics and Space Agency (grant no. NAG2–1507) and with support from Wake Forest University's Science Research and Research and Publication Funds.
2 Present address: Australian Research Council Centre of Excellence for Integrative Legume Research, Genomic Interactions Group, Research School of Biological Sciences, Australian National University, Sullivan's Creek Road, Acton, ACT 2601, Australia.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Gloria Muday (muday{at}wfu.edu).
[W] The online version of this article contains Web-only data.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.075671.
* Corresponding author; e-mail muday{at}wfu.edu; fax 336–758–6008.
Received December 15, 2005;
returned for revision January 26, 2006;
accepted February 5, 2006.
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