Differences in the light‐dependent changes of the glutathione metabolism during cold acclimation in wheat varieties with different freezing tolerance

Light‐dependent (250 or 500 µmol/m2/s, red/far‐red: 15/1; 250 µmol/m2/s and red/far‐red: 10/1) adjustment of glutathione metabolism during cold acclimation (5°C, 7 d) was compared in four wheat genotypes (14‐day‐old) differing in freezing tolerance. Only the shoot fresh weight of the two tolerant genotypes increased during cold, regardless of light conditions. Their electrolyte leakage was decreased in high light intensity. Cold greatly increased both the amount of γ‐glutamylcysteine (glutathione precursor) and cysteinylglycine (degradation product) in all genotypes grown in high intensity and far‐red lights, and consequently, the ratio of their oxidised forms exhibited a great decrease. However, cold induced a fivefold increase in the amount of glutathione and hydroxymethylglutathione disulphides only in the two sensitive genotypes grown in far‐red light. In general, the activities of the four enzymes of ascorbate–glutathione cycle were decreased by cold, except for the two tolerant genotypes cultivated in high light intensity. The gene expression studies did not reveal any transcriptional control of the changes observed at metabolite and activity levels. Our results show that both high intensity and far‐red lights are involved in the control of the cold‐induced changes in the amount/activity of the studied antioxidants, and some of these alterations have positive correlation with the level of freezing tolerance.