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
â??electron transport', involving an enzyme called ferredoxin: NADP(H)
oxidoreductase, or FNR. Plants switch rapidly between two types of
electron transport â?? 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.

SE - Scientistsâ?? discovery ends long-standing photosynthesis controversy
- Queen Mary University of London (qmul.ac.uk)
[www.qmul.ac.uk]