title: Valinomycin sensitivity proves that light-induced thylakoid voltages result in millisecond phase of chlorophyll fluorescence transients.
abstract: Upon sudden exposure of plants to an actinic light of saturating intensity, the yield of chlorophyll fluorescence increases typically by 200-400% of the initial O-level. At least three distinct phases of these O-J-I-P transients can be resolved: O-J (0.05-5 ms), J-I (5-50 ms), and I-P (50-1000 ms). In thylakoid membranes, the J-I increase accounts for approximately 30% of the total fluorescence increase; in Photosystem II membranes, the J-I phase is always lacking. In the presence of the ionophore valinomycin, which is known to inhibit specifically the formation of membrane voltages, the magnitude of the J-I phase is clearly diminished; in the presence of valinomycin supplemented by potassium, the J-I phase is fully suppressed. We conclude that the light-driven formation of the thylakoid-membrane voltage results in an increase of the chlorophyll excited-state lifetime, a phenomenon explainable by the electric-field-induced shift of the free-energy level of the primary radical pair [Dau and Sauer, Biochim. Biophys. Acta 1102 (1992) 91]. The assignment of the J-I increase in the fluorescence yield enhances the potential of using O-J-I-P fluorescence transients for investigations on photosynthesis in intact organisms. A putative role of thylakoid voltages in protection of PSII against photoinhibitory damage is discussed.
authors.affiliation: FB Physik, Freie Universität Berlin, Arminallee 14, D-14195 -Dahlem, Berlin, Germany.
authors.forename: Pavel
authors.initials: P
authors.lastname: Pospísil
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002734:Chlorophyll; D004594:Electrophysiology; D005453:Fluorescence; D008027:Light; D018724:Spinacia oleracea; D020524:Thylakoids / Q000187:drug effects / Q000502:physiology*; D014634:Valinomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D002734:Chlorophyll; D014634:Valinomycin