Fig. 3: Light-driven redox reactions in Mn-depleted PSII tracked by optical spectroscopy.
a, b UV–vis absorption spectra. The orange line (triangles) represents a suspension of Mn-depleted PSII before the addition of DCPIP (60 µM) serving as artificial electron acceptor (buffer conditions: 1 M glycine-betaine, 15 mM NaCl, 5 mM CaCl2, 5 mM MgCl2, 25 mM MES buffer, pH 7; for further details see SI). Then DCPIPox and either 5 µM MnCl2 (in a) or 240 µM MnCl2 (in b) were added, followed by continuous white-light illumination (1000 µE m−2 s−1) of the PSII suspensions and collection of spectra (one spectrum per minute; immediately prior to illumination, red lines, and after 3 min light, blue lines). The green and light-green lines correspond to the spectral contributions of DCPIPox to the dark and 3-min light spectra; the amplitude decrease at 604 nm represents the loss of DCPIPox due to its reduction by PSII (arrows). The dark-yellow dotted spectra are assignable to a Mn oxide, as verified by X-ray absorption spectroscopy (spectra obtained by weighted spectral deconvolution, see caption of Supplementary Fig. 6, and scaled by a factor of 5, for clarity). Note that significant spectral changes due to Mn-oxide formation were only observed with 240 µM MnCl2 (in b), but not with 5 µM MnCl2 (in a). Source data are provided as a Source Data file.
