1, 2, 4-triazole derivatives, including tebuconazole, have been reported to show positive physiological effects in cereals apart from fungicidal activity and to increase plants’ tolerance against temperature stress. This study investigates the mechanisms of increasing frost resistance of etiolated winter wheat (Triticum aestivum L., “Irkutskaya” variety) seedlings by tebuconazole-based seed dresser “Bunker” (1.5 μL g⁻¹ of seeds) and tebuconazole (30 μg g⁻¹ of seeds). To identify ABA-dependent and ABA-independent pathways of frost resistance, we used fluridone (FLD, 5 mg L⁻¹), an inhibitor of endogenous abscisic acid (ABA) synthesis. FLD effectively inhibited the accumulation of carotenoids in the shoots and prevented the formation of carotenoids caused by the “Bunker” and tebuconazole. In non-hardened seedlings, FLD stimulated coleoptile and first leaf growth, but did not suppress the growth inhibitory effects of “Bunker” and tebuconazole. In shoots of hardened seedlings, FLD reduced the retarding effect of tebuconazole. Regardless of seedling age, temperature, and the protectant treatment, FLD had no effect on the sugar content in the shoots. FLD did not essentially influence frost resistance induced by “Bunker” and tebuconazole in cold-hardened seedlings. Fluridone increased H₂O₂ content and guaiacol peroxidase activity under control conditions (both with tebuconazole and without tebuconazole) and during cold hardening (in seedlings from seeds treated with tebuconazole). ABA levels in cold-hardened seedlings treated with FLD alone, tebuconazole alone, or a combination of the two were two to three times lower than in untreated hardened seedlings. Changes in indole-3-acetic and salicylic acids in response to FLD and tebuconazole treatment indicate complex interactions with signaling cellular systems. Our results suggest that tebuconazole activates ABA-independent pathways more strongly than ABA-dependent pathways in enhancing frost resistance. The potential mechanisms of tebuconazole action in plant cells are discussed.

Synthetic auxins are used in agriculture as herbicides worldwide, which leads to localized pollution and their potential entry into food crops during early developmental stages. Triticum aestivum L. is a major agricultural crop, and for this reason, understanding the mechanisms by which herbicides affect photosynthetic and lipid metabolic processes in wheat is crucial for assessing yield reduction risks. This study aimed to evaluate the toxic effects of three synthetic auxins, 1-naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D), and clopyralid (CLD) on growth parameters, membrane permeability, lipid peroxidation (LPO) product content, fatty acid (FA) profiles, and photosynthetic pigment levels in both etiolated and green spring wheat seedlings. FA content was assessed using gas chromatography-mass spectrometry. The results revealed that NAA and 2,4-D exerted the most pronounced inhibitory effects on seedling growth, whereas 2,4-D and CLD increased membrane permeability. In etiolated seedlings exposed to synthetic auxins, there was an elevation in FA content noted. Conversely, in green seedlings, exposure to all tested synthetic auxins led to a reduction in FA content, particularly affecting polyunsaturated fatty acids (PUFAs), as well as declines in chlorophyll and carotenoid levels. CLD reduced odd-chain fatty acid content (OCFAs) and very long-chain fatty acid content (VLCFAs) to undetectable levels. The increase in LPO products under the action of 2,4-D and CLD indicates oxidative stress as a possible cause of the decrease in PUFA content in green seedlings. These findings suggest that synthetic auxins have detrimental impacts on the photosynthetic apparatus of wheat, which in turn may have negative consequences for its productivity.