The response of etiolated seedlings of winter rye (Secale cereale), bread (Triticum aestivum) and durum (T. durum) wheats, as well as triticale (× Triticosecale) to the action of hyperthermia in relation to their resistance to oxidative stress was studied. Exposure of seedlings to 45°C for 4 hours led to a significant inhibition of the growth of T. aestivum, while the growth of T. durum and × Triticosecale seedlings was less sensitive to hyperthermia, and S. cereale seedlings showed the greatest resistance to heat stress. In bread wheat seedlings after heating, intensive development of oxidative stress. In durum wheat and triticale, such effects were less pronounced, and in rye, they were almost absent. In rye, triticale, and durum wheat seedlings, peroxidase activity increased under hyperthermia conditions, while in bread wheat, on the contrary, it decreased. In all four studied cereals, in response to the action of high temperature, the content of multifunctional stress metabolite proline increased, however, in rye, its absolute content significantly exceeded that in other species. The content of sugars during hyperthermia increased in S. cereale and T. durum, but did not change in the other two cereals. Triticale and especially rye have a high base content of anthocyanins and its increase in response to high temperature. A conclusion was made about the relationship between the ability of cereal seedlings to maintain growth under the action of hyperthermia and their resistance to oxidative stress, which is mainly due to the accumulation of metabolites with antioxidant activity.

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The functioning of the stress-protective systems of wheat under the action of cold at the early stages of plant development remains poorly studied. The aim of this work was a comparative study of antioxidant activity and the content of sugars and proline as indicators of osmoprotective activity during cold adaptation of seedlings of seven winter bread wheat (Triticum aestivum L.) cultivars that differ significantly in frost resistance. The 3-day-old etiolated seedlings were hardened at 2°C for 6 days and then frozen for 5 h at -6 or -9°C. Two days after freezing, the survival of seedlings was assessed by their ability to grow. A decrease in ROS content, an increase in the activity of antioxidant enzymes catalase and guaiacol peroxidase and accumulation of sugars in the shoots of high-frost-resistant cultivars during hardening were detected. The absolute values of catalase and guaiacol peroxidase activity correlated positively with the frost resistance of seedlings. The negative correlation between the frost tolerance of the cultivars and the accumulation of proline in the seedlings during hardening was recorded. The possibility of using the studied biochemical indices for frost resistance screening of winter wheat varieties at the seedling stage was stated. Keywords: antioxidant system, cold hardening, frost resistance, osmolytes, oxidative stress, Triticum aestivum