Evaluating the efficiency of vitamin B12 biofortification on performance of thyme (Thymus vulgaris L.) exposed to freezing stress

This study evaluated vitamin B12 in mitigating freezing stress in thyme (Thymus vulgaris). Treatments included two temperatures (25°C and −5°C) and foliar VB12 application (0 and 100 mg L−1), applied once and twice. Freezing (−5°C) severely damaged roots and reduced shoot biomass by 84%. Although VB12 enhanced growth in non-stressed plants (height: 34 cm, diameter: 63 cm, fresh weight: 232 g), it did not alleviate freezing stress effects. In the absence of VB12, electrolyte leakage increased tenfold under stress, with VB12 having minimal impacts on membrane permeability. A single VB12 application increased Fv/Fm by 31.36%, and non-photochemical quenching declined by 49.5% under freezing. Photosynthetic pigments and chlorophyll stability index increased during stress but declined post-recovery. VB12 application had no effect on malondialdehyde content under stress but reduced levels post-recovery (51.8 and 45.4 μmol g−1 fresh weight for one and two applications, respectively). Hydrogen peroxide levels were 61.16% under stress, decreasing to 56.62% after recovery with one-time VB12 application. These findings suggest that VB12-treated plants’ reductions in electrolyte leakage and reactive oxygen detoxification may improve thyme’s freezing tolerance.