Kinetics of the fluorescence yield F/F0 in a leaf infiltrated with water. F0, dark-adapted fluorescence yield. After 6.2-s illumination (kiPSII ∼84 s−1), a 200-ms pulse of strong light (kiPSII ∼1600 s−1) that fully reduces QA is given. Curve 1, the leaf is dark-adapted for 6 h. Curve 2, the same leaf as for curve 1 is submitted to repetitive cycles (>3) of 6.2 s of light and 7 min of dark. 1′ and 2′, maximum fluorescence yield Fmax reached at the end of the 200-ms pulse for curves 1 and 2, respectively.