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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Multicellularity and the functional interdependence of motility and molecular transport
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Multicellularity and the functional interdependence of motility and molecular transport

机译：多细胞性与运动性和分子运输的功能相互依赖

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Benefits, costs, and requirements accompany the transition from motile totipotent unicellular organisms to multicellular organisms having cells specialized into reproductive (germ) and vegetative (sterile soma) functions such as motility. In flagellated colonial organisms such as the volvocalean green algae, organized beating by the somatic cells' flagella yields propulsion important in pho-totaxis and chemotaxis. It has not been generally appreciated that for the larger colonies flagellar stirring of boundary layers and remote transport are fundamental for maintaining a sufficient rate of metabolite turnover, one not attainable by diffusive transport alone. Here, we describe experiments that quantify the role of advective dynamics in enhancing productivity in germ soma-differentiated colonies. First, experiments with suspended de-flagellated colonies of Volvox carteri show that forced advection improves productivity. Second, particle imaging velocimetry of fluid motion around colonies immobilized by micropipette aspiration reveals flow fields with very large characteristic velocities U extending to length scales exceeding the colony radius R. For a typical metabolite diffusion constant D, the associated Peclet number Pe = 2UR/D 1, indicative of the dominance of advection over diffusion, with striking augmentation at the cell division stage. Near the colony surface, flows generated by flagella can be chaotic, exhibiting mixing due to stretching and folding. These results imply that hydrodynamic transport external to colonies provides a crucial boundary condition, a source for supplying internal diffusional dynamics.
机译：收益，成本和要求伴随着从运动型全能单细胞生物到具有细胞专门化为生殖（生殖）和营养（无菌躯体）功能（例如运动）的多细胞生物的转变。在鞭毛状的殖民地生物中，例如顺氟萘绿藻中，由体细胞鞭毛组织的跳动产生的推进作用对光趋化和趋化性很重要。人们通常不认识到，对于较大的菌落，边界层的鞭毛搅动和远距离运输对于维持足够的代谢产物周转率是根本的，而仅通过扩散运输是无法实现的。在这里，我们描述了量化对流动力学在提高生殖细胞分化的菌落生产力中的作用的实验。首先，对Volvox Carteri的无鞭毛悬浮菌落进行悬浮实验表明，强制对流可提高生产率。其次，通过微量移液器抽吸固定化菌落周围流体运动的颗粒成像测速显示了具有非常大的特征速度U的流场，该特征速度U扩展到超过菌落半径R的长度尺度。对于典型的代谢物扩散常数D，相关的Peclet数Pe = 2UR / D 1，表明对流占主导地位的扩散，在细胞分裂阶段显着增加。在菌落表面附近，鞭毛产生的血流可能是混乱的，由于拉伸和折叠而表现出混合。这些结果表明，菌落外部的水动力输送提供了关键的边界条件，这是提供内部扩散动力学的来源。

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