ATP‐induced photochemical quenching of variable chlorophyll fluorescence

ATP induces rapid quenching of fluorescence yield in light‐activated class D chloroplasts, distinguishable from the slower quenching caused by protein phosphorylation. The mechanism of the rapid quenching is shown to be photochemical, by application of the saturation pulse method with a modulated measuring system [(1986) Photosynth. Res. 10, 51‐62]. The effect is most pronounced at relatively low light intensities (optimum 2 ) without addition of electron acceptors. The properties of the ATP‐induced quenching with respect to ionophores, uncouplers and ATPase inhibitors suggest involvement of the reversible, light‐activated thylakoid ATPase. As a working hypothesis, it is proposed that part of PS II reaction centers, which are stroma‐exposed and in close proximity to CF0‐CF1, are modified by ATPase activity. Transformation of cytochromeb‐559 high‐potential form to low‐potential form by membrane acidification is discussed as a possible mechanism.