Abstract
Photosystem I (PSI) cyclic electron transport is essential for efficient photosynthesis. However, the route taken by electrons is still unclear. Recently, it was found that the cytochrome b6f complex associates with the FNR and contains an novel heme, which is not conserved in the cytochrome bc1 complex. Based on the findings, it was suggested that the cytochrome b6f complex was related with the PGR5-dependent cyclic pathway.
We evaluated whether the PGR5-depenedent pathway is through the cytochrome b6f complex or not by using an Arabidopsis mutant, pgr1(proton gradient regulation). In pgr1, Q-cycle activity is hypersensitive to acidification of the thylakoid lumen because of an amino acid alternation in the Rieske subunit of the cytochrome b6f complex. Neither in vivo nor in vitro assays showed that the defect in Q-cycle activity affected the PGR5-dependent pathway. It is suggested that Fd donates electrons directly to PQ in PGR5-dependent pathway.
