Fig. 2

Maximum quantum yield efficiency of PSII (Fv/Fm) in unfrozen Arabidopsis leaves (UFC, 1D-UFC, 3D-UFC, 6D-UFC) and in leaves frozen to different temperatures right after thawing (RAT) or after recovery for 1 day (1D-REC), 3 days (3D-REC) or 6 days (6D-REC) at 4 °C for a non-acclimated plants and b cold acclimated plants. Control samples were incubated at 4 °C for the respective times. Three independent experiments were carried out for each temperature except for − 5 °C, − 7 °C, − 11 °C and − 12 °C with only one and − 13 °C with two experiments. Data are means of 10 to 15 biological replicates per experiment with standard errors. Significance levels between values measured at UFC/RAT and at the subsequent time points determined by Student’s t-test are indicated as: ***, p < 0.001, **, p < 0.01, *, p < 0.05