Kim S K, Chang S C, Lee E J, Chung W S, Kim Y S, Hwang S, Lee J S
Department of Life Science, Chung-Ang University, Seoul 156-756, Korea.
Plant Physiol. 2000 Jul;123(3):997-1004. doi: 10.1104/pp.123.3.997.
Exogenously applied brassinolide (BL, 10(-9)-10(-5) M) increased gravitropic curvature in maize (Zea mays) primary roots. The BL-enhanced gravitropic curvature was clearly promoted in the presence of indole-3-acetic acid (IAA, 10(-10)-10(-8) M), indicating that BL is interactive with IAA during the gravitropic response. The interactive effect between BL and IAA was completely diminished by treatment of p-chlorophenoxy isobutric acid, an auxin action antagonist. The activation of the gravitropic response by BL in the absence and in the presence of IAA was nullified by application of 2, 3,5-triiodobenzoic acid, a polar auxin transport inhibitor. The data indicate that brassinosteroids (BRs) might be involved in auxin-mediated processes for the gravitropic response. Gas chromotography-selected ion-monitoring analysis revealed that maize primary roots contained approximately 0.3 ng g(-1) fresh weight castasterone as an endogenous BR. Exogenously applied castasterone also increased the gravitropic response of maize roots in an IAA-dependent manner. This study provides the first evidence, to our knowledge, for occurrence and gravitropic activity of BRs in plant roots.
外源施加油菜素内酯（BL，10⁻⁹ - 10⁻⁵ M）可增加玉米（Zea mays）初生根的向重力性弯曲。在吲哚 - 3 - 乙酸（IAA，10⁻¹⁰ - 10⁻⁸ M）存在的情况下，BL增强的向重力性弯曲明显增强，这表明在向重力性反应过程中BL与IAA存在相互作用。用生长素作用拮抗剂对氯苯氧异丁酸处理后，BL与IAA之间的相互作用完全消失。在不存在和存在IAA的情况下，BL对向重力性反应的激活作用都被极性生长素运输抑制剂2,3,5 - 三碘苯甲酸消除。这些数据表明油菜素类固醇（BRs）可能参与了生长素介导的向重力性反应过程。气相色谱 - 选择离子监测分析表明，玉米初生根含有约0.3 ng g⁻¹鲜重的内源性BR——油菜素甾酮。外源施加油菜素甾酮也以依赖IAA 的方式增加了玉米根的向重力性反应。据我们所知，本研究首次提供了BRs在植物根中存在及其向重力性活性的证据。
