The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
J R Soc Interface. 2012 Apr 7;9(69):640-7. doi: 10.1098/rsif.2011.0395. Epub 2011 Aug 24.
The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork's bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.
植物的固着特性要求其发展种子扩散机制以建立新的生长位置。许多物种的扩散策略涉及到扩散单元的干燥，这会导致基于环境湿度变化的定向收缩和运动。大多数研究过的吸湿扩散机制都基于双层结构。在这里，我们研究了依靠螺旋芒收紧和放松来推动自身穿过表面进入安全发芽位置的鹳嘴（臭矢菜属）种子的运动性。我们表明，这种运动是基于由机械均匀组织组成的特殊单层。细胞壁结构中的纤维素微纤维以异常倾斜的螺旋排列，导致每个细胞螺旋化。这些细胞通过集体螺旋形成宏观线圈。一个由嵌入各向同性泡沫基质中的线制成的简单模型表明，这种纤维素排列确实足以诱导细胞的螺旋化。
