In shoots of the garden pea, the bioactive gibberellin (GA 1) is synthesised from GA 20, and the enzyme which catalyses this step (a GA 3-oxidase-PsGA3ox1) is encoded by Mendel's LE gene. It has been reported previously that decapitation of the shoot (excision of the apical bud) dramatically reduces the conversion of [ 3H]GA 20 to [ 3H]GA 1 in stems, and here we show that endogenous GA 1 and PsGA3ox1 transcript levels are similarly reduced. We show also that these effects of decapitation are completely reversed by application of the auxin indole-3-acetic acid (IAA) to the 'stump' of decapitated plants. Gibberellin A 20 is also converted to an inactive product, GA 29, and this step is catalysed by a GA 2-oxidase, PsGA2ox1. In contrast to PsGA3ox1, PsGA2ox1 transcript levels were increased by decapitation and reduced by IAA application. Decapitation and IAA treatment did not markedly affect the level of GA 1 precursors. It is suggested that in intact pea plants, auxin from the apical bud moves into the elongating internodes where it (directly or indirectly) maintains PsGA3ox1 transcript levels and, consequently, GA 1 biosynthesis.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Physiology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Environmental Sciences
Author:	Ross, JJ (Associate Professor John Ross)
Author:	O'Neill, DP (Mr Damian O'Neill)
Author:	Smith, JJ (Ms Jenny Smith)
Author:	Kerckhoffs, LH (Dr Leonardus Kerckhoffs)
Author:	Elliott, RC (Dr Robert Elliott)
ID Code:	20581
Year Published:	2000
Web of Science® Times Cited:	170
Deposited By:	Plant Science
Deposited On:	2000-08-01
Last Modified:	2011-08-04
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