Four-week-old wild-type (Col-0) and 3 independent VPZ lines (nos. 2, 4 and 7) grown under 12 h light/12 dark cycles (see Methods) were dark-adapted (20 min) to determine minimal and maximal fluorescence (Fo, Fm), then exposed to high light (500 μmol photons m-2 s-1) for 2 h and partially dark-adapted (10 min) to monitor Fo’ and Fm’. Photoprotection index, residual NPQ and maximum quantum yield of PSII (Fv/Fm) after partial dark adaptation are presented. Data are presented as the mean ± s.d. for n = 16 independent plants (indicated in circles) from 4 independent experiments and statistical differences from WT according to a two-tailed Student’s t-test (P ≤ 0.05) are indicated.