Brown algal male gametes show chemotaxis to the sex pheromone that is released from female gametes. The chemotactic behavior of the male gametes is controlled by the changes in the beating of two flagella known as the anterior and posterior flagellum. Our previous study using Mutimo cylindricus showed that the sex pheromone induced an increment in both the deflection angle of the anterior flagellum and sustained unilateral bend of the posterior flagellum, but the mechanisms regulating these two flagellar waveforms were not fully revealed. In this study, we analyzed the changes in swimming path and flagellar waveforms with a high-speed recording system under different calcium conditions. The extracellular Ca²⁺ concentration at 10⁻³ M caused an increment in the deflection angle of the anterior flagellum only when ionomycin was absent. No sustained unilateral bend of the posterior flagellum was induced either in the absence or presence of ionomycin in extracellular Ca²⁺ concentrations below 10⁻² M. Real-time Ca²⁺ imaging revealed that there is a spot near the basal part of anterior flagellum showing higher Ca²⁺ than in the other parts of the cell. The intensity of the spot slightly decreased when male gametes were treated with the sex pheromone. These results suggest that Ca²⁺-dependent changes in the anterior and posterior flagellum are regulated by distinct mechanisms and that the increase in the anterior flagellar deflection angle and sustained unilateral bend of the posterior flagellum may not be primarily induced by the Ca²⁺ concentration.

中文翻译：

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褐藻Mutimo cylindricus（Cutleriaceae，Tilopteridales）雄配子趋化过程中钙对两条鞭毛的独特调节

褐藻雄性配子对雌性配子释放的性信息素表现出趋化性。雄配子的趋化行为是由称为前鞭毛和后鞭毛的两个鞭毛的跳动变化控制的。我们之前使用Mutimo cylindricus的研究表明，性信息素诱导前鞭毛偏转角度的增加和后鞭毛的持续单侧弯曲，但调节这两种鞭毛波形的机制尚未完全揭示。在本研究中，我们利用高速记录系统分析了不同钙条件下游泳路径和鞭毛波形的变化。仅当不存在离子霉素时，10 ^-3 M的细胞外Ca ²⁺浓度 才导致前鞭毛的偏转角增加。无论细胞外Ca ²⁺浓度低于10 ^-2 M ，离子霉素存在或不存在均不会诱导后鞭毛持续单侧弯曲。 实时Ca ²⁺成像显示前鞭毛基部附近有一个斑点显示出比细胞其他部分更高的 Ca ²⁺ 。当用性信息素处理雄性配子时，斑点的强度略有下降。这些结果表明，前鞭毛和后鞭毛的 Ca ²⁺依赖性变化是由不同的机制调节的，并且前鞭毛偏转角度的增加和后鞭毛的持续单侧弯曲可能不是主要由 Ca ²⁺浓度引起的。