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Motility and phototaxis of Gonium, the simplest differentiated colonial alga.
Physical Review E ( IF 2.2 ) Pub Date : 2020-02-24 , DOI: 10.1103/physreve.101.022416
Hélène de Maleprade 1 , Frédéric Moisy 2 , Takuji Ishikawa 3 , Raymond E Goldstein 1
Affiliation  

Green algae of the Volvocine lineage, spanning from unicellular Chlamydomonas to vastly larger Volvox, are models for the study of the evolution of multicellularity, flagellar dynamics, and developmental processes. Phototactic steering in these organisms occurs without a central nervous system, driven solely by the response of individual cells. All such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light. The flagella of Chlamydomonas and Volvox both exhibit an adaptive response to such signals in a manner that allows for accurate phototaxis, but in the former the two flagella have distinct responses, while the thousands of flagella on the surface of spherical Volvox colonies have essentially identical behavior. The planar 16-cell species Gonium pectorale thus presents a conundrum, for its central 4 cells have a Chlamydomonas-like beat that provide propulsion normal to the plane, while its 12 peripheral cells generate rotation around the normal through a Volvox-like beat. Here we combine experiment, theory, and computations to reveal how Gonium, perhaps the simplest differentiated colonial organism, achieves phototaxis. High-resolution cell tracking, particle image velocimetry of flagellar driven flows, and high-speed imaging of flagella on micropipette-held colonies show how, in the context of a recently introduced model for Chlamydomonas phototaxis, an adaptive response of the peripheral cells alone leads to photoreorientation of the entire colony. The analysis also highlights the importance of local variations in flagellar beat dynamics within a given colony, which can lead to enhanced reorientation dynamics.

中文翻译:


最简单的分化群落藻类 Gonia 的运动性和趋光性。



团藻谱系的绿藻,从单细胞衣藻到更大的团藻,是研究多细胞进化、鞭毛动力学和发育过程的模型。这些生物体中的趋光转向没有中枢神经系统,仅由单个细胞的反应驱动。所有这些藻类在游泳时都会绕着身体固定的轴旋转。因此,当该轴未与光对齐时,每个单元上的定向光电传感器都会接收周期性信号。衣藻团藻的鞭毛都以允许精确趋光的方式对此类信号表现出适应性反应,但在前者中,两个鞭毛具有不同的反应,而球形团藻菌落表面上的数千个鞭毛具有基本相同的行为。因此,平面 16 细胞物种胸骨藻提出了一个难题,因为它的中央 4 个细胞具有类似衣藻的节拍,可以提供垂直于平面的推进力,而它的 12 个外围细胞则通过类似团藻的节拍产生围绕法线的旋转。在这里,我们结合实验、理论和计算来揭示Gium (也许是最简单的分化群体生物)如何实现趋光性。高分辨率细胞跟踪、鞭毛驱动流的粒子图像测速以及微量移液器固定菌落上鞭毛的高速成像表明,在最近引入的衣藻趋光性模型的背景下,仅外围细胞的适应性反应如何导致整个群体的光重定向。 该分析还强调了给定群体内鞭毛搏动动力学局部变化的重要性,这可能导致增强的重新定向动力学。
更新日期:2020-02-24
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