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J Exp Bot. 2007;58(15-16):4269-81. doi: 10.1093/jxb/erm288.

Ethylene-induced Arabidopsis hypocotyl elongation is dependent on but not mediated by gibberellins.

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  • 1Unit of Plant Hormone Signaling & Bio-imaging, Department of Molecular Genetics, Ghent University, Ledeganckstraat 35, B-9000 Ghent, Belgium.


Ethylene, or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), can stimulate hypocotyl elongation in the light. It is questioned whether gibberellins (GAs) play a role in this response. Tests with light of different wavelengths demonstrated that the ethylene response depends on blue light and functional cryptochrome signalling. Levels of bio-active GA(4) were reduced in seedlings showing an ethylene response. Furthermore, ACC treatment of seedlings caused accumulation of the DELLA protein RGA, a repressor of growth. Concurrently, transcript levels of several GA biosynthesis genes were up-regulated and GA inactivation genes down-regulated by ACC. Hypocotyl elongation in response to ACC was strongly reduced in seedlings with a diminished GA signal, while being vigorously stimulated in a quadruple DELLA knock-out mutant with constitutive GA signalling. These data show that ethylene-driven hypocotyl elongation is mainly blue light-dependent and that this ethylene response, although GA dependent, hence needing a basal GA level, is not mediated by GA, but rather acts via a separate pathway.

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