Fig. 4

Cold tolerance assay of PtrA/NINV-overexpressing transgenic plants. a Phenotype of two-week-old plants before and after exposure to −1 °C for 24 h and after recovery at room temperature for 3 days. b Survival rate of wild type (WT) and transgenic lines after recovery (n = 20). c-d Chlorophyll fluorescence imaging (c) and maximum quantum efficiency of the photochemistry (Fv/Fm, d) after the cold treatment of two-week-old plants, which were displayed by Imaging WinGegE software (Walz, Effeltrich, Germany). The false colour scale between 0 and 1 is shown below the imaging. Bar = 5 cm. e-f Electrolyte leakage (EL, e) and MDA (f) of 45-days-old plants before and after the cold treatments, which were measured using sampled leaves. Statistically significant differences between the transgenic lines and WT under the same conditions are shown (*P < 0.05, **P < 0.01, ***P < 0.001)