PDF(Pubmed)
Abstract：
Marine phytoplankton vary widely in size across taxa, and in cell suspension densities across habitats and growth states. Cell suspension density and total biovolume determine the bulk influence of a phytoplankton community upon its environment. Cell suspension density also determines the intercellular spacings separating phytoplankton cells from each other, or from co-occurring bacterioplankton. Intercellular spacing then determines the mean diffusion paths for exchanges of solutes among co-occurring cells. Marine phytoplankton and bacterioplankton both produce and scavenge reactive oxygen species (ROS), to maintain intracellular ROS homeostasis to support their cellular processes, while limiting damaging reactions. Among ROS, hydrogen peroxide (H2O2) has relatively low reactivity, long intracellular and extracellular lifetimes, and readily crosses cell membranes. Our objective was to quantify how cells can influence other cells via diffusional interactions, using H2O2 as a case study. To visualize and constrain potentials for cell-to-cell exchanges of H2O2, we simulated the decrease of [H2O2] outwards from representative phytoplankton taxa maintaining internal [H2O2] above representative seawater [H2O2]. [H2O2] gradients outwards from static cell surfaces were dominated by volumetric dilution, with only a negligible influence from decay. The simulated [H2O2] fell to background [H2O2] within ~3.1 µm from a Prochlorococcus cell surface, but extended outwards 90 µm from a diatom cell surface. More rapid decays of other, less stable ROS, would lower these threshold distances. Bacterioplankton lowered simulated local [H2O2] below background only out to 1.2 µm from the surface of a static cell, even though bacterioplankton collectively act to influence seawater ROS. These small diffusional spheres around cells mean that direct cell-to-cell exchange of H2O2 is unlikely in oligotrophic habits with widely spaced, small cells; moderate in eutrophic habits with shorter cell-to-cell spacing; but extensive within phytoplankton colonies.
摘要：
海洋浮游植物在分类单元中的大小差异很大，以及栖息地和生长状态下的细胞悬浮液密度。细胞悬浮液密度和总生物体积决定了浮游植物群落对其环境的总体影响。细胞悬浮密度也决定了浮游植物细胞彼此分离的细胞间距，或者来自共存的浮游细菌。细胞间间距然后决定了共现细胞间溶质交换的平均扩散路径。海洋浮游植物和浮游细菌都产生和清除活性氧（ROS），维持细胞内ROS稳态以支持其细胞过程，同时限制破坏性反应。在ROS中，过氧化氢（H2O2）具有相对较低的反应性，长的细胞内和细胞外寿命，并且容易穿过细胞膜。我们的目标是量化细胞如何通过扩散相互作用影响其他细胞，使用H2O2作为案例研究。为了可视化和限制H2O2的细胞间交换潜力，我们模拟了[H2O2]从代表性浮游植物类群向外减少，并将内部[H2O2]保持在代表性海水[H2O2]之上。从静态细胞表面向外的[H2O2]梯度由体积稀释主导，衰变的影响微不足道。模拟的[H2O2]下降到背景[H2O2]在〜3.1µm内，但从硅藻细胞表面向外延伸90微米。其他的更快衰减，不太稳定的ROS，会降低这些阈值距离。浮游细菌将模拟的局部[H2O2]降低到背景以下，仅从静态细胞表面到1.2µm，即使浮游细菌共同影响海水ROS。细胞周围的这些小的扩散球意味着H2O2的直接细胞与细胞交换不太可能发生在具有广泛间隔的寡营养习惯中，小细胞；富营养化习性适中，细胞间间距较短；但在浮游植物菌落内广泛存在。
