CeBiTec – Colloquium
Monday, July 08, 2019, 17 c.t.
G2-104, CeBiTec Building
Prof. Chikahiro Miyake
Graduate School of Agriculture, Kobe University, Japan
P700 Oxidation Suppresses the Production of Reactive Oxygen Species (ROS) in Photosystem I and Induces Ferredoxin-Independent Cyclic Electron Flow within PSI
O2-evolving photosynthesis organisms oxidize reaction center chlorophyll, P700, in photosystem (PS) I of thylakoid membranes to suppress ROS production. The oxidation of P700 is a robust strategy for them to survive under natural environments. P700 carries electrons from plastocyanin to ferredoxin (Fd) in the photo-oxidation reduction cycle of P700 in PSI. Accumulation of excited P700, P700*, increases chances to electron donation to O2 and energy transfer to O2 producing superoxide radical in Mehler reaction and singlet O2, which oxidatively inactivate PSI to inhibit photosynthesis. Photosynthesis organisms have diverse mechanisms to oxidize P700: to stimulate oxidation of P700*, flavodiiron proteins and photorespiration can be an effective electron sink; to suppress reduction of oxidized P700, P700+, proton conductance, gH+, can regulate the acidification of the lumen of thylakoids to control the activity of Cyt b6/f-complex. These factors cooperate to suppress ROS production in PSI as “P700 oxidation system”.
We furthermore researched the regulation of P700 oxidation by ferredoxin (Fd) in intact leaves of higher plants using DUAL/KLAS-NIR (WALZ, Germany), which Ulrich Schreiber and Christof Klughammer developed. P700 oxidation induced the extra electron flux in PSI, not coupled with the redox reaction of Fd, which was driven by photosynthesis and photorespiration. We proposed charge recombination could drive Fd-independent cyclic electron flow within PSI, and will discuss its physiological functions.
Host: Prof. Dr. Karl-Josef Dietz