plant dark adaption using light saturation pulse intensity of 3750 µmol photons/(m2 s) for 800 ms. Subsequently, the minimum fluorescence signal (when all PSII centers are in the open state) from dark-adapted material (F0) and the maximum fluorescence signal (when all PSII centers are in the closed state) from dark-adapted material (Fm) were measured, and photosystem II (PSII) maximum efficiency within dark-adapted material (Fv/Fm) was calculated. The amount of survived shoots, dry matter of above-ground mass and roots (g per leaf or shoot depending on the growth phase) after one week from cold stress were also recorded.
All measurements were done in 15 replications on fully developed leaves of randomly selected plants. The experimental data were analyzed by multifactor analysis of variance. The significance of differences between means was determined using the Tukey’s test at the significance level P < 0.05 and P < 0.01.