Abstract In aquatic environments, phytoplankton represent a major source of reactive oxygen species (ROS) such as superoxide and hydrogen peroxide. Many phytoplankton taxa also produce extracellular ROS under optimal growth conditions in culture. However, the physiological purpose of extracellular ROS production by phytoplankton and its wider significance to ecosystem-scale trophic interactions and biogeochemistry remain unclear. Here, we review the rates, taxonomic diversity, subcellular mechanisms and functions of extracellular superoxide and hydrogen peroxide production by phytoplankton with a view towards future research directions. Model eukaryotic phytoplankton and cyanobacteria produce extracellular superoxide and hydrogen peroxide at cell-normalized rates that span several orders of magnitude, both within and between taxa. The potential ecophysiological roles of extracellular ROS production are versatile and appear to be shared among diverse phytoplankton species, including ichthyotoxicity, allelopathy, growth promotion, and iron acquisition. Whereas extracellular hydrogen peroxide likely arises from a combination of intracellular and cell surface production mechanisms, extracellular superoxide is predominantly generated by specialized systems for transplasma membrane electron transport. Future insights into the molecular-level basis of extracellular ROS production, combined with existing high-sensitivity geochemical techniques for the direct quantification of ROS dynamics, will help unveil the ecophysiological and biogeochemical significance of phytoplankton-derived ROS in natural aquatic systems.

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浮游植物产生细胞外活性氧：过去和未来的方向

摘要 在水生环境中，浮游植物是活性氧 (ROS) 的主要来源，如超氧化物和过氧化氢。许多浮游植物分类群也在培养的最佳生长条件下产生细胞外 ROS。然而，浮游植物产生细胞外活性氧的生理目的及其对生态系统规模的营养相互作用和生物地球化学的更广泛意义仍不清楚。在这里，我们回顾了浮游植物产生细胞外超氧化物和过氧化氢的速率、分类多样性、亚细胞机制和功能，以期展望未来的研究方向。模型真核浮游植物和蓝藻以跨越几个数量级的细胞标准化速率产生细胞外超氧化物和过氧化氢，包括分类群内部和分类群之间。细胞外 ROS 产生的潜在生态生理作用是多方面的，似乎在不同的浮游植物物种之间共享，包括鱼鳞毒性、化感作用、生长促进和铁获取。细胞外过氧化氢可能由细胞内和细胞表面产生机制的组合产生，而细胞外超氧化物主要由跨质膜电子传递的专门系统产生。未来对细胞外 ROS 产生的分子水平基础的深入了解，结合现有的用于直接量化 ROS 动力学的高灵敏度地球化学技术，将有助于揭示浮游植物来源的 ROS 在天然水生系统中的生态生理和生物地球化学意义。