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Gravistimulation leads to asymmetry of both auxin and gibberellin levels in barley pulvini


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Wolbang, CM, Davies, NW, Taylor, SA and Ross, JJ 2007 , 'Gravistimulation leads to asymmetry of both auxin and gibberellin levels in barley pulvini' , Physiologia Plantarum, vol. 131, no. 1 , pp. 140-148 , doi: 10.1111/j.1399-3054.2007.00931.x.

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The auxin indole-3-acetic acid (IAA) is known to promote the biosynthesis of
active gibberellins (GAs) in barley (Hordeum vulgare). We therefore investigated
the possibility that this interaction might contribute to the gravitropic
response of barley leaf sheath pulvini. Barley plants at the inflorescence stage
were gravistimulated for varying times, and the pulvini were then separated
into upper and lower halves for quantification of IAA and GAs by GC-MS.
Consistent with the Cholodny–Went theory, the lower portion contained more
IAA than did the upper portion. This difference was detected as early as 2.5 h
after the start of gravistimulation, and bending was also observed at this stage.
At later time points tested (6 h and 24 h), but not at 2.5 h or 3 h, the higher auxin
content of the lower half was associated with a higher level of GA1, the main
bioactive GA in barley. Consistent with that result, the expression of Hv3ox2,
which encodes a key enzyme for the conversion of GA20 to GA1, was higher in
the lower side than in the upper, after 6 h. It is suggested that in gravistimulated
leaf sheath pulvini, auxin accumulates in the lower side, leading to a higher
level of GA1, which contributes to the bending response. Further evidence that
GAs play a role in the gravitropic response was obtained from GA-related
mutants, including the elongated sln1c mutant, in which GA signalling is
constitutive. Pulvinar bending in the sln1c mutant was greater than in the wildtype.
This result indicates that in the lower side of the gravistimulated pulvinus,
the relatively high level of bioactive GA facilitates, but does not mediate, the
bending response.

Item Type: Article
Authors/Creators:Wolbang, CM and Davies, NW and Taylor, SA and Ross, JJ
Journal or Publication Title: Physiologia Plantarum
Publisher: Wiley-Blackwell Munksgaard
ISSN: 0031-9317
DOI / ID Number: 10.1111/j.1399-3054.2007.00931.x
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