The Laboratory, Marine Biological Association, Citadel Hill, Plymouth, PL1 2PB, UK.
Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4QD, UK.
New Phytol. 2021 Apr;230(1):155-170. doi: 10.1111/nph.17162. Epub 2021 Jan 24.
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 Ca signalling is involved in diatom osmotic sensing. However, mechanistic insight of the role of osmotic Ca signalling is limited. Here, we show that Phaeodactylum Ca elevations are essential for surviving hypo-osmotic shock. Moreover, employing novel single-cell imaging techniques we have characterised real-time Ca signalling responses in single diatom cells to environmental osmotic perturbations. We observe that intracellular spatiotemporal patterns of osmotic-induced Ca elevations encode vital information regarding the nature of the osmotic stimulus. Localised Ca 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 Ca -independent and dependent mechanisms for osmoregulation. We find that efflux of organic osmolytes occurs in a Ca -independent manner, but this response is insufficient to mitigate cell damage during hypo-osmotic shock. By comparison, Ca -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.
硅藻是全球重要的浮游植物，主导着沿海和极地冰区的生物群落。这些环境的盐度在动态时空范围内发生显著变化。快速的感应系统对于减轻渗透胁迫的有害后果至关重要。基于种群的分析表明，钙信号参与了硅藻的渗透感应。然而，渗透钙信号作用的机制见解有限。在这里，我们表明，泡叶藻的钙升高对于在低渗冲击下存活是必不可少的。此外，我们采用新颖的单细胞成像技术，实时地研究了单个硅藻细胞对环境渗透压扰动的钙信号响应。我们观察到，渗透诱导的钙升高的细胞内时空模式编码了有关渗透压刺激性质的重要信息。由轻度或逐渐低渗冲击引起的局部钙信号从顶端细胞尖端全局传播，从而能够在整个细胞中精细地调节细胞体积。最后，我们证明了硅藻采用钙依赖和非依赖的机制进行渗透调节。我们发现，有机渗透物的外排以钙非依赖的方式发生，但这种反应不足以在低渗冲击期间减轻细胞损伤。相比之下，钙依赖信号对于通过精确协调 K 转运来防止细胞爆裂是必要的，因此可能是在动态渗透压环境中生存的基础。
