FIGURE 1.

Effects of extended dark exposure on photosynthetic parameters in wild type (Ws) and mutants affecting ATP synthase regulation. Wild-type (Ws) (gray circles), 35S::ATPC1 in dpa1 (comp, white diamonds), gamera-1 (white gray triangles), and gamera-2 (black triangles) were subjected to extended dark exposure for four days. Illumination was minimized to prevent substantial activation of photosynthetic energy storage. A single saturation pulse was given for measurement of FV/FM, followed by 20 min 20 μmol photons m^-2 s^-1 illumination and a second saturation pulse for estimation of linear electron flow (LEF). (A,B) The maximum quantum yield of PSII (FV/FM) was estimated by chlorophyll a fluorescence imaging. The red and blue false coloring indicates high and low FV/FM values, as indicated in the key. (C) Light-driven linear electron flow (LEF) under steady-state illumination was calculated, based on chlorophyll a fluorescence parameters as described in Material and methods. (D) Fractional changes in the proton conductivity across the thylakoid membrane (gH+), estimated by the decay kinetics of the electrochromic shift (ECS), reflecting the activity of the chloroplast ATP synthase. The gH+ data was normalized to values at time zero, at which point Ws, 35S::ATPC1 in dpa1(comp), gamera-1 and gamera-2 showed relative gH+ values of 97.8 ± 7.6, 78.6 ± 2.1, 46.9 ± 7.3, and 41.0 ± 8.0 s-1, respectively. All measurements were averages of independent experiments on biological replicates (n = 4–5).