The shape effect of flagella is more important than bottom-heaviness on passive gravitactic orientation in Chlamydomonas reinhardtii
The shape effect of flagella is more important than bottom-heaviness on passive gravitactic orientation in Chlamydomonas reinhardtii
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DOI：
10.1242/jeb.205989
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发表时间：
2020-03-01
影响因子：
2.8
通讯作者：
Ishikawa, Takuji
中科院分区：
文献类型：
--
作者：
Kage, Azusa;Omori, Toshihiro;Ishikawa, Takuji
单细胞、双鞭毛、绿藻衣藻向上定向的方式早已在力学和生理学方面进行了讨论。在这项研究中，我们主要关注引力轴的力学，即“被动”机制。要使身体向上旋转，细胞的不对称至关重要。衣藻可以被描绘成一个近球形的细胞体，有两个前对称的鞭毛。目前的研究着眼于问题是否存在的鞭毛显著影响扭矩产生向上重新定向。“密度不对称模型”假设细胞是球形的，底部很重，鞭毛的形状和重量可以忽略不计，而“形状不对称模型”则考虑鞭毛的形状。我们的实验和模拟结果都表明，形状不对称对莱茵衣藻向上取向的贡献相当大，比密度不对称的贡献大几倍。根据实验结果，我们还量化了底重的程度，即假设胞体为球形时，重心与图形之间的距离。我们的估计约为30 nm，仅为先前假设的三分之一。这些发现表明，在衣藻中，鞭毛向上的粘性阻力的重要性，从而导致负重力轴。
The way the unicellular, biflagellated, green alga Chlamydomonas orients upward has long been discussed in terms of both mechanics and physiology. In this study, we focus on the mechanics, i.e. the 'passive' mechanisms, of gravitaxis. To rotate the body upwards, cellular asymmetry is critical. Chlamydomonas can be depicted as a nearly spherical cell body with two anterior, symmetric flagella. The present study looks at the question of whether the existence of the flagella significantly affects torque generation in upward reorientation. The `density asymmetry model' assumes that the cell is spherical and bottom-heavy and that the shape and weight of the flagella are negligible, while the `shape asymmetry model' considers the shape of the flagella. Both our experimental and simulation results revealed a considerable contribution from shape asymmetry to the upward orientation of Chlamydomonas reinhardtii, which was several times larger than that of density asymmetry. From the experimental results, we also quantified the extent of bottom-heaviness, i.e. the distance between the centers of gravity and the figure when the cell body is assumed to be spherical. Our estimation was approximately 30 nm, only one-third of previous assumptions. These findings indicate the importance of the viscous drag of the flagella to the upward orientation, and thus negative gravitaxis, in Chlamydomonas.