Biology Department Seminar

Nonphotochemical quenching (NPQ) comprises mechanisms by which photosynthetic organisms harmlessly dissipate excess absorbed light energy. Photoinhibitory quenching, qI, thought to be the result of photoinactivation of photosystem II, is the slowest component of NPQ to relax and is the least understood. The possibility that part of qI may be photoprotective has been little examined, in part because of the lack of mutants directly affecting qI. Through two consecutive rounds of suppressor genetic screens in the model plant Arabidopsis thaliana, we identified a factor that negatively regulates this form of energy dissipation (SOQ1) and subsequently found a factor required for this energy dissipation to occur (CHL). The CHL gene encodes for the chloroplastic lipocalin protein, which is predicted to bind small hydrophobic molecules and is hypothesized to function in the prevention and/or management of lipid peroxidation. We found that the CHL-dependent NPQ mechanism operates under stress conditions such as cold and high light, and our results suggest that SOQ1 inhibits CHL-dependent quenching under non-stress conditions. Examination of this form of energy dissipation will provide valuable clues to increase photosynthetic efficiency through crop development.