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Auxin-Gibberellin Interactions in Pea: Integrating the Old with the New


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Ross, JJ, O'Neill, DP and Rathbone, DA 2003 , 'Auxin-Gibberellin Interactions in Pea: Integrating the Old with the New' , Journal of plant growth regulation, vol. 227, no. 1 , pp. 99-108 , doi: 10.1007/s00344-003-0021-z.

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Recent findings on auxin-gibberellin interactions in
pea are reviewed, and related to those from studies
conducted in the 1950s and 1960s. It is now clear
that in elongating internodes, auxin maintains the
level of the bioactive gibberellin, GA1, by promoting
GA1 biosynthesis and by inhibiting GA1 deactivation.
These effects are mediated by changes in expression
of key GA biosynthesis and deactivation
genes. In particular, auxin promotes the step GA20
to GA1, catalyzed by a GA 3-oxidase encoded by
Mendel’s LE gene. We have used the traditional
system of excised stem segments, in which auxin
strongly promotes elongation, to investigate the
importance for growth of auxin-induced GA1. After
excision, the level of GA1 in wild-type (LE) stem
segments rapidly drops, but the auxin indole-3-
acetic acid (IAA) prevents this decrease. The growth
response to IAA was greater in internode segments
from LE plants than in segments from the le-1 mutant,
in which the step GA20 to GA1 is impaired.
These results indicate that, at least in excised segments,
auxin partly promotes elongation by increasing
the content of GA1. We also confirm that
excised (light-grown) segments require exogenous
auxin in order to respond to GA. On the other hand,
decapitated internodes typically respond strongly to
GA1 application, despite being auxin-deficient. Finally,
unlike the maintenance of GA1 content by
auxin, other known relationships among the
growth-promoting hormones auxin, brassinosteroids,
and GA do not appear to involve large changes
in hormone level.

Item Type: Article
Authors/Creators:Ross, JJ and O'Neill, DP and Rathbone, DA
Journal or Publication Title: Journal of plant growth regulation
ISSN: 0721-7595
DOI / ID Number: 10.1007/s00344-003-0021-z
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