Gallenmüller Friederike, Langer Max, Poppinga Simon, Kassemeyer Hanns-Heinz, Speck Thomas
Plant Biomechanics Group, Botanic Garden, University of Freiburg, Freiburg im Breisgau, Germany.
Freiburg Materials Research Center (FMF), Freiburg im Breisgau, Germany.
AoB Plants. 2017 Dec 23;10(1):plx075. doi: 10.1093/aobpla/plx075. eCollection 2018 Feb.
The ability to perform hygroscopic movements has evolved in many plant lineages and relates to a multitude of different functions such as seed burial, flower protection or regulation of diaspore release. In most mosses, spore release is controlled by hygroscopic movements of the peristome teeth and also of the spore capsule. Our study presents, for the first time, temporally and spatially well-resolved kinematic analyses of these complex shape changes in response to humidity conditions and provides insights into the sophisticated functional morphology and anatomy of the peristome teeth. In the outer teeth of the peristome perform particularly complex hygroscopic movements during hydration and desiccation. Hydration induces fast inward dipping followed by partial re-straightening of the teeth. In their final shape, wet teeth close the capsule. During desiccation, the teeth perform an outward flicking followed by a re-straightening which opens the capsule. We present a kinematic analysis of these shape changes and of the underlying functional anatomy of the teeth. These teeth are shown to be composed of two layers which show longitudinal gradients in their material composition, structure and geometry. We hypothesize that these gradients result in (i) differences in swelling/shrinking capacity and velocity between the two layers composing the teeth, and in (ii) a gradient of velocity of swelling and shrinking from the tip to the base of the teeth. We propose these processes explain the observed movements regulating capsule opening or closing. This hypothesis is corroborated by experiments with isolated layers of peristome teeth. During hydration and desiccation, changes to the shape and mass of the whole spore capsule accompany the opening and closing. Results are discussed in relation to their significance for humidity-based regulation of spore release.
许多植物谱系都进化出了进行吸湿运动的能力，这与多种不同功能相关，如种子掩埋、花朵保护或传播体释放的调节。在大多数苔藓中，孢子的释放由齿舌齿以及孢子囊的吸湿运动控制。我们的研究首次对这些复杂的形状变化在时间和空间上进行了高分辨率的运动学分析，以响应湿度条件，并深入了解了齿舌齿复杂的功能形态和解剖结构。在水化和干燥过程中，齿舌的外齿会进行特别复杂的吸湿运动。水化会导致牙齿快速向内倾斜，随后部分重新伸直。在最终形状中，湿润的牙齿会封闭孢子囊。在干燥过程中，牙齿会向外弹动，随后重新伸直，从而打开孢子囊。我们对这些形状变化以及牙齿潜在的功能解剖结构进行了运动学分析。这些牙齿由两层组成，在材料组成、结构和几何形状上呈现纵向梯度。我们假设这些梯度导致：（i）构成牙齿的两层之间在肿胀/收缩能力和速度上存在差异，以及（ii）从牙齿尖端到基部的肿胀和收缩速度梯度。我们认为这些过程解释了观察到的调节孢子囊打开或关闭的运动。用分离的齿舌齿层进行的实验证实了这一假设。在水化和干燥过程中，整个孢子囊的形状和质量变化伴随着打开和关闭。我们将讨论这些结果对于基于湿度的孢子释放调节的意义。
