花粉孔的机械设计与花粉粒的内折
Mechanical design of apertures and the infolding of pollen grain
摘要：
当花粉粒暴露在环境中时，它们迅速干燥。为了保护自己直到再水化，谷物在谷物壁的特殊结构-孔-的帮助下进行特征性的内折叠，在孔中，否则厚的外壁壳不存在或厚度减少。最近的理论研究已经强调了孔的弹性响应和粮食的折叠的重要性。实验观察表明，不同的花粉粒共享相同的数量和类型的孔，但可以折叠在相当不同的方式。使用薄壳弹性理论，我们展示了如何绝对的弹性特性的花粉壁以及外壁和孔隙之间的相对弹性差异起着重要的作用，在确定花粉折叠干燥。我们主要关注沟道花粉，描绘了花粉弹性参数的区域，其中干燥导致所有孔隙定期、完全关闭，从而导致内折叠，保护谷物免受水分损失。花粉折叠路径的相图表明，孔的数量的增加导致弹性参数的区域的减少，其中孔以规则的方式关闭。内折还取决于孔的形状和大小的细节，我们的研究解释了孔的机械设计的功能如何影响花粉折叠模式。理解花粉折叠路径背后的力学原理也应该被证明是有用的人工非均匀壳的弹性响应的设计。
英文摘要：
When pollen grains become exposed to the environment, they rapidly desiccate. To protect themselves until rehydration, the grains undergo characteristic infolding with the help of special structures in the grain wall---apertures---where the otherwise thick exine shell is absent or reduced in thickness. Recent theoretical studies have highlighted the importance of apertures for the elastic response and the folding of the grain. Experimental observations show that different pollen grains sharing the same number and type of apertures can nonetheless fold in quite diverse fashion. Using thin-shell theory of elasticity, we show how both the absolute elastic properties of the pollen wall as well as the relative elastic differences between the exine wall and the apertures play an important role in determining pollen folding upon desiccation. Focusing primarily on colpate pollen, we delineate the regions of pollen elastic parameters where desiccation leads to a regular, complete closing of all apertures and thus to an infolding which protects the grain against water loss. Phase diagrams of pollen folding pathways indicate that an increase in the number of apertures leads to a reduction of the region of elastic parameters where the apertures close in a regular fashion. The infolding also depends on the details of the aperture shape and size, and our study explains how the features of the mechanical design of apertures influence the pollen folding patterns. Understanding the mechanical principles behind pollen folding pathways should also prove useful for the design of the elastic response of artificial inhomogeneous shells.
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