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At present hydrogen sulfide (H 2 S) is considered as one of the signal mediators in plant cells. However, its role in formation of plant resistance to low temperatures and, in particular, in regulation of secondary metabolism under stress conditions remains poorly understood. The influence of H 2 S donor sodium hydrosulfide (NaHS) on phenylalanine ammonia-lyase (PAL) activity and content of flavonoids in wheat seedlings at normal temperature (21 °C) and under cold hardening conditions (7 days at 3 °C) was studied. After 2 days of the hardening temperature, a transient increase in PAL activity was noted. Also, activity of the enzyme was increased by treatment of plants with 0.1 or 0.5 mM NaHS under normal temperature conditions and especially at the background of cold hardening. By themselves, the cold hardening and the action of H 2 S donor caused an increase in total content of flavonoids and amount of anthocyanins. With the combination of hypothermia and treatment of seedlings with NaHS, this effect enlarged and the total content of flavonoids increased by 3.8, and anthocyanins increased by 1.8 times in comparison to the control. Treatment with the H 2 S donor caused a decrease in content of the lipid peroxidation product malonic dialdehyde in seedlings after the action of hardening temperature, and especially after their freezing at-5 °C. Also, under the influence of NaHS, survival of hardened and unhardened seedlings after cryostress increased. It was concluded that one of the mechanisms of the positive influence of the H 2 S donor on resistance of wheat seedlings to hypothermia is the PAL-dependent accumulation of flavonoid compounds, which have a high antioxidant activity, and a decrease in effects of secondary oxidative stress. K e y w o r d s: hydrogen sulfide (H 2 S), phenylalanine ammonia-lyase, flavonoids, lipid peroxidation, frost resistan ce, Triticum aestivum. A t present, the functions of hydrogen sulfide (H 2 S) as a signal mediator in mammalian cells have been well studied; its involvement in regulation of vascular tone, neuromodulation, cytoprotection, inflammation, and apoptosis was established [1-3]. The role of hydrogen sulfide in plant cells is investigated significantly weaker, but

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