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Abstract

The auxin indole-3-acetic acid (IAA) has been shown to promote the biosynthesis of the active gibberellin (GA1) in shoots
of pea (Pisum sativum). We used northern analysis to investigate the timing of IAA-induced changes in transcript levels of
PsGA3ox1 (Mendel’s LE), PsGA2ox1, PsGA2ox2, and PsGA20ox1, key genes for the later stages of GA1 biosynthesis and
metabolism in pea. Rapid (2–4 h) changes occurred in the transcript levels of PsGA3ox1, PsGA2ox1, and PsGA2ox2 after
treatent with IAA. [14C]GA1 metabolism studies in decapitated shoots indicated that IAA inhibits GA1 deactivation, consistent
with the suppression of PsGA2ox1 (SLN) transcript levels by IAA. Studies with the sln mutant also indicated that
PsGA2ox1 activity is involved in GA1 deactivation in decapitated shoots. Culture of excised internode tissue in the presence of
auxin clearly demonstrated that internode tissue is a site of GA1 biosynthesis per se. Excised internode tissue cultured in the
presence/absence of cycloheximide showed that de novo protein synthesis is required for IAA-induced increases in PsGA3ox1
transcript levels. Auxin dose response studies indicated that IAA concentration is a critical determinant of GA1 biosynthesis
over 1 to 2 orders of magnitude, and a range of auxins was shown to affect the GA pathway.

Item Type:	Article
Authors/Creators:	O'Neill, DP and Ross, JJ
Journal or Publication Title:	Plant Physiology
ISSN:	0032-0889
DOI / ID Number:	https://doi.org/10.1104/pp.010587
Additional Information:	Copyright 2002 American Society of Plant Biologists
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