The dynamics of catalase (CaT) and guaiacol peroxidase (POD) activity in winter wheat (Triticum aestivum L.) leaves under exposure to a low hardening temperature of 4°C for 7 days was studied. It was established that the freezing tolerance of the seedlings increased already after 1 hour of exposure, and then continued to grow, reaching a maximum on the 7th day. The content of malondialdehyde increased slightly during the first 2 days of cold exposure and then declined, possibly pointing to attenuation of the oxidative stress in plant cells. It was also found that the activity of one of the key antioxidant enzymes involved in hydrogen peroxide (h2O2) recycling – CaT, increased after
1 hour of cold exposure. CaT activity then continued to increase, reaching a maximum on the 2nd day, with a decline following afterwards. along with this, POD activity increased throughout the cold hardening period. In addition, a slight increase in H2O2 content in leaves was detected during the first 24 hours of cold exposure, but then H2O2 level in the cells decreased towards the end of chilling. Based on these data we can conclude that the increase in the activity of antioxidant enzymes plays an important role in promoting the tolerance to hypothermia in wheat. CaT and POD are involved in h2O2 recycling at
the initial stage of low-temperature adaptation in the plants, whereas later on POD plays the main role in this process. Thus, the activation of antioxidant enzymes in leaves prevents the development of oxidative stress and promotes the tolerance of low temperature in wheat.