Abstract：
Exploding seed pods of the common weed Cardamine hirsuta have the remarkable ability to launch seeds far from the plant. The energy for this explosion comes from tension that builds up in the fruit valves. Above a critical threshold, the fruit fractures along its dehiscence zone and the two valves coil explosively, ejecting the seeds. A common mechanism to generate tension is drying, causing tissues to shrink. However, this does not happen in C. hirsuta fruit. Instead, tension is produced by active contraction of growing exocarp cells in the outer layer of the fruit valves. Exactly how growth causes the exocarp tissue to contract and generate pulling force is unknown. Here we show that the reorientation of microtubules in the exocarp cell cortex changes the orientation of cellulose microfibrils in the cell wall and the consequent cellular growth pattern. We used mechanical modeling to show how tension emerges through growth due to the highly anisotropic orientation of load-bearing cellulose microfibrils and their effect on cell shape. By explicitly defining the cell wall as multi-layered in our model, we discovered that a cross-lamellate pattern of cellulose microfibrils further enhances the developing tension in growing cells. Therefore, the interplay of cell wall properties with turgor-driven growth enables the fruit exocarp to generate sufficient tension to power explosive seed dispersal.
摘要：
普通杂草Cardaminehirsuta的爆炸种子豆荚具有显着的能力，可以远离植物发射种子。这种爆炸的能量来自水果阀门中积聚的张力。超过临界阈值，果实沿着其开裂区断裂，两个瓣膜爆发性盘绕，喷射种子。产生张力的常见机制是干燥，导致组织收缩。然而,这不会发生在C.hirsuta水果中。相反，张力是由果实瓣膜外层生长的外皮细胞的主动收缩产生的。确切地,生长如何导致外皮组织收缩并产生拉力是未知的。在这里，我们表明，外皮细胞皮质中微管的重新定向会改变细胞壁中纤维素微纤维的方向以及随之而来的细胞生长方式。我们使用机械建模来显示由于承载纤维素微纤维的高度各向异性取向及其对细胞形状的影响，张力如何通过生长出现。通过在我们的模型中明确定义细胞壁为多层，我们发现，纤维素微纤维的交叉层状图案进一步增强了生长细胞的发育张力。因此,细胞壁特性与膨润驱动的生长的相互作用使水果外果皮能够产生足够的张力，以推动爆炸性的种子扩散。
