Department of Mechanical Engineering, Faculty of Systems Science and Technology, Akita Prefectural University, Yurihonjo, Akita, 015-0055, Japan.
Graduate School of Natural Science, Konan University, Kobe, Hyogo, 658-8501, Japan.
Sci Rep. 2023 Jul 17;13(1):11165. doi: 10.1038/s41598-023-38069-x.
Gravitropism is the plant organ bending in response to gravity, while a straightening mechanism prevents bending beyond the gravitropic set-point angle. The promotion and prevention of bending occur simultaneously around the inflorescence stem tip. How these two opposing forces work together and what part of the stem they affect are unknown. To understand the mechanical forces involved, we rotated wild type and organ-straightening-deficient mutant (myosin xif xik) Arabidopsis plants to a horizontal position to initiate bending. The mutant stems started to bend before the wild-type stems, which led us to hypothesize that the force preventing bending was weaker in mutant. We modeled the wild-type and mutant stems as elastic rods, and evaluated two parameters: an organ-angle-dependent gravitropic-responsive parameter (β) and an organ-curvature-dependent proprioceptive-responsive parameter (γ). Our model showed that these two parameters were lower in mutant than in wild type, implying that, unexpectedly, both promotion and prevention of bending are weak in mutant. Subsequently, finite element method simulations revealed that the compressive stress in the middle of the stem was significantly lower in wild type than in mutant. The results of this study show that myosin-XIk-and-XIf-dependent organ straightening adjusts the stress distribution to achieve a mechanically favorable shape.
向重性是植物器官在重力作用下弯曲的现象，而一个直化机制可以防止弯曲超过向重设定角度。弯曲的促进和阻止在花序茎尖周围同时发生。这两种相反的力是如何协同作用的，以及它们影响茎的哪个部分，目前还不清楚。为了了解所涉及的力学力，我们将野生型和器官直化缺陷突变体（肌球蛋白 Xif xik）拟南芥植株旋转到水平位置以启动弯曲。突变体茎在野生型茎之前开始弯曲，这使我们假设阻止弯曲的力在突变体中较弱。我们将野生型和突变体茎建模为弹性杆，并评估了两个参数：一个器官角度依赖的向重响应参数（β）和一个器官曲率依赖的本体感受响应参数（γ）。我们的模型表明，这两个参数在突变体中都低于野生型，这表明出乎意料的是，弯曲的促进和阻止在突变体中都较弱。随后，有限元方法模拟表明，野生型茎中间的压缩应力明显低于突变体。这项研究的结果表明，肌球蛋白 XIk 和 XIf 依赖性器官直化调整了应力分布，以达到有利的机械形状。
