Figure 2. Characterization of cytochrome b₆f complex in the Q_iKO strain.

(a) Immunoblot chemiluminescence analysis of the major subunits of cytochrome b₆f. Subunit β of chloroplast ATPase as a loading control. Q_iKO shows wild-type level of all cytochrome b₆f subunits with the doublet signature for cytochrome b₆ missing the c_i haem after SDS-urea PAGE. (b) Covalent haem peroxidasic activity confirms the absence of the c_i haem in Q_iKO strain. (c) Dithionite minus ascorbate spectra from purified b₆f complexes. Black, WT; red, Q_iKO. Haems b (peaks at 434 and 564 nm) and c_i (broad band at 425 nm) components36; in Q_iKO the decreased amplitude at 434 and 564 nm demonstrates the absence of b_h and the trough at 420 nm the absence of c_i. The spectra have been normalized to the cytochrome f content (inset).