Figure 6.

Blue-Green Light–Induced Fluorescence Quenching in Iron-Starved Wild-Type and ΔisiA Cells.

(A) to (C) The 0 d (green), 7 d (data not shown; similar to 0 d), 10 d (red), 12 d (blue), and 14 d (black) iron-starved ΔIsiA (A) and wild-type ([B] and [C]) cells (at 3 μg chlorophyll/mL) were dark-adapted and then illuminated successively with low-intensity blue-green light (400 to 550 nm, 80 μmol photons m⁻² s⁻¹) and high-intensity blue-green light (740 μmol photons m⁻² s⁻¹). Saturating pulses were applied to measure maximal fluorescence levels. Fm, maximal fluorescence under low intensities of blue light; Fm′, maximal fluorescence under high intensities of blue light; Fs, steady state fluorescence; Fo, minimal fluorescence (see [C]). In (C), the changes of fluorescence traces in 7 and 14 d iron-starved wild-type cells are shown with a different scale than (A) and (B) to clarify the differences in fluorescence quenching.

(D) Increase of NPQ [(Fm − Fm′)/Fm′] during iron starvation of wild-type (circles and solid line) and ΔIsiA (squares and dotted line) cells. The graph is the average of four independent experiments. Error bars show the maximum and minimum NPQ values for each point.