The Effects of Auxin on the Mechanical Properties in Vivo of Cell Wall in Hypocotyl Segments from Gibberellin-Deficient Cowpea Seedlings : GROWTH AND DEVELOPMENT

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Auxin-induced changes in the mechanical properties of cell wall were examined by both positive and negative pressure jump methods using hypocotyl segments excised from the 3-day-old seedlings of cowpea that has been treated with uniconazole, a potent inhibitor of the biosynthesis of gibberellins. In such segments (U-segments) that were deficient in endogenous gibberellin, auxin increased only the effective turgor (P^i-Y) and did not change the extensibility (Φ) of cell wall. As a result, the extent of the auxin-induced promotion of growth was halved. However, auxin was able to increase Φ of U-segments that has been pretreated for two hours with GA_3 prior to the application of IAA. Measurement of intracellular pressure (P^i) with a pressure probe revealed that auxin did not change P^i in either U-segments or GA_3-pretreated segments. The results suggest that auxin can decrease the yield threshold of the cell wall (Y) independently of gibberellin but can increase Φ only in the presence of gibberellin. The difference between Φ and Y in terms of their requirement for gibberellin to respond to auxin suggests that they are mutually separable mechanical properties that originate from different molecular processes that occur in the architecture of yielding cell walls.
日本植物生理学会の論文