Discovery Ends Long-Standing Photosynthesis Controversy

Scientists from the Queen Mary University of London have identified the location in plant cells of a key enzyme involved in photosynthesis. The findings overturn the conventional belief about where the enzyme resides in plant cells and suggest a likely role in regulating energy processes as plants adapt from dark to light conditions.

During photosynthesis, carbon is converted into energy stores through ‘electron transport', involving an enzyme called ferredoxin: NADP(H) oxidoreductase, or FNR. Plants switch rapidly between two types of electron transport – linear electron flow (LEF) and cyclic electron flow (CEF) in response to environmental conditions. The FNR transfer between membrane structures in the chloroplast, where photosynthesis takes place, has been linked to this switch. The belief is that FNR carries out its function in the soluble compartment of the chloroplast, but evidence suggests that the activity of FNR increases when it is attached to an internal membrane.

The team tested how FNR location affects electron transport. In normal dark-adapted plants, short exposure to light resulted in a switch to higher CEF activity. However, this was not seen in plants lacking strong interaction between FNR and tether proteins, suggesting these plants lack the ability to switch on CEF. After light acclimatization, both the wild-type and mutant plants had similar, decreased CEF activity, suggesting that the impact of FNR is related to light-dependent changes in the interactions between the enzyme and tether proteins.

"Our results show a link between the interaction of FNR with different proteins and the activity of an alternative photosynthetic electron transport pathway," concludes senior author Guy Hanke, Senior Lecturer in Plant Cell and Molecular Biology at Queen Mary. He added that their findings support a role for FNR location in regulating photosynthetic electron flow during the transition of plants from dark to light.

For more details, read the article on the Queen Mary University of London website.