Fig. 4.

The oxidative stress induced by turbulent cues reduces photosynthetic efficiency and growth rate of H. akashiwo. (A) Maximum photosynthetic quantum yield, F_v/F_m, of H. akashiwo cells before and after turbulence-induced population splits. A PAM chlorophyll fluorometer was used to assess the maximum quantum yield of photosystem II on single cells collected from the top (n = 26) and bottom (n = 25) of the chamber after exposure to rolling (Ω = 1 rad · s⁻¹) for 5 min and from cells not exposed to rolling (Control, n = 25). All cells were dark-adapted for 15 min before measurements. Boxes show ±1 SD, whiskers ±2 SD, and the central line indicates the mean. Control and flipped populations differed significantly (one-way ANOVA, F_2,74 = 18.8, P < 0.001). Brackets show P values from post hoc Tukey’s HSD tests (SI Appendix, Table S2). (B) Increase in cell concentration with time for the subpopulations extracted from the top (red) and bottom (blue) of the chamber after exposure to rolling (Ω = 1 rad · s⁻¹) for 5 min (mean ± SD of three replicates). Cells were regrown from the same initial density. The intrinsic growth rate, g, was quantified for each subpopulation by fitting an exponential function (dashed curves; g_↑ = 0.74 ± 0.02 d⁻¹, g_↓ = 0.47 ± 0.03 d⁻¹).