• Diatoms are globally important phytoplankton that dominate coastal and polar‐ice assemblages. These environments exhibit substantial changes in salinity over dynamic spatiotemporal regimes. Rapid sensory systems are vital to mitigate the harmful consequences of osmotic stress. Population‐based analyses have suggested that Ca²⁺ signalling is involved in diatom osmotic sensing. However, mechanistic insight of the role of osmotic Ca²⁺ signalling is limited.
• Here, we show that Phaeodactylum Ca²⁺ elevations are essential for surviving hypo‐osmotic shock. Moreover, employing novel single‐cell imaging techniques we have characterised real‐time Ca²⁺ signalling responses in single diatom cells to environmental osmotic perturbations.
• We observe that intracellular spatiotemporal patterns of osmotic‐induced Ca²⁺ elevations encode vital information regarding the nature of the osmotic stimulus. Localised Ca²⁺ signals evoked by mild or gradual hypo‐osmotic shocks are propagated globally from the apical cell tips, enabling fine‐tuned cell volume regulation across the whole cell.
• Finally, we demonstrate that diatoms adopt Ca²⁺‐independent and dependent mechanisms for osmoregulation. We find that efflux of organic osmolytes occurs in a Ca²⁺‐independent manner, but this response is insufficient to mitigate cell damage during hypo‐osmotic shock. By comparison, Ca²⁺‐dependent signalling is necessary to prevent cell bursting via precise coordination of K⁺ transport, and therefore is likely to underpin survival in dynamic osmotic environments.

中文翻译：

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细胞内 Ca2+ 信号的时空模式控制海洋硅藻的低渗透应力恢复

• 硅藻是全球重要的浮游植物，主导着沿海和极地冰的组合。这些环境在动态时空状态下表现出盐度的显着变化。快速感觉系统对于减轻渗透压力的有害后果至关重要。基于群体的分析表明，Ca ²⁺信号传导参与硅藻渗透传感。^{然而，对渗透性 Ca 2+}信号传导作用的机理认识是有限的。
• 在这里，我们证明了Phaeodactylum Ca ²⁺的升高对于低渗透性休克的存活至关重要。此外，采用新的单细胞成像技术，我们已经表征了单个硅藻细胞对环境渗透扰动的实时 Ca ²⁺信号反应。
• 我们观察到渗透诱导的 Ca ²⁺升高的细胞内时空模式编码了有关渗透刺激性质的重要信息。由轻度或逐渐低渗透性休克引起的局部 Ca ²⁺信号从顶端细胞尖端全局传播，从而能够在整个细胞中进行微调的细胞体积调节。
• 最后，我们证明硅藻采用 Ca ²⁺独立和依赖机制进行渗透调节。我们发现有机渗透物的流出以不依赖 Ca ²⁺的方式发生，但这种反应不足以减轻低渗透休克期间的细胞损伤。相比之下，Ca ^{2+依赖的信号传导对于通过精确协调 K +}转运来防止细胞破裂是必要的，因此很可能支持在动态渗透环境中的存活。