The Effects of Auxin on the Mechanical Properties in Vivo of Cell Wall in Hypocotyl Segments from Gibberellin-Deficient Cowpea Seedlings |
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Authors: | Okamoto Akane; Katsumi Masayuki; Okamoto Hisashi |
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Institution: | 1School of Integrated Science, Yokohama City University Yokohama, 236 Japan
2Department of Biology, International Christian University Tokyo, 118 Japan |
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Abstract: | Auxin-induced changes in the mechanical properties of cell wallwere examined by both positive and negative pressure jump methodsusing hypocotyl segments excised from the 3-day-old seedlingsof cowpea that has been treated with uniconazole, a potent inhibitorof the biosynthesis of gibberellins. In such segments (U-segments)that were deficient in endogenous gibberellin, auxin increasedonly the effective turgor (PiY) and did not change theextensibility ( ) of cell wall. As a result, the extent of theauxin-induced promotion of growth was halved. However, auxinwas able to increase of U-segments that has been pretreatedfor two hours with GA3 prior to the application of IAA. Measurementof intracellular pressure (Pi) with a pressure probe revealedthat auxin did not change Pi in either U-segments or GA3-pretreatedsegments. The results suggest that auxin can decrease the yieldthreshold of the cell wall (Y) independently of gibberellinbut can increase only in the presence of gibberellin. The differencebetween and Y in terms of their requirement for gibberellinto respond to auxin suggests that they are mutually separablemechanical properties that originate from different molecularprocesses that occur in the architecture of yielding cell walls.
3Present address: Ohishi, Enden, Mori-machi, Shuchi-gun, Shizuoka,437-02 Japan |
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