Light-dependent single-cell heterogeneity in the chloroplast redox state regulates cell fate in a marine diatom

Diatoms are photosynthetic microorganisms of great ecological and biogeochemical importance, forming vast blooms in aquatic ecosystems. However, we are still lacking fundamental understanding of individual cells sense and respond to diverse stress conditions, and what acclimation strategies employed during bloom dynamics. We investigated cellular responses to environmental stress at single-cell level using the roGFP sensor targeted to various organelles in the diatom Phaeodactylum tricornutum. We detected cell-to-cell variability using flow cytometry cell sorting and a microfluidics system for live imaging of roGFP oxidation dynamics. Chloroplast-targeted roGFP exhibited a light dependent, bi-stable oxidation pattern in response to H₂O₂ and high light, revealing distinct subpopulations of sensitive oxidized cells and resilient reduced cells. Early oxidation in the chloroplast preceded commitment to cell death, and can be used for sensing stress cues and regulating cell fate. propose that light-dependent metabolic heterogeneity regulates diatoms’ sensitivity to environmental stressors in the ocean.