ROS-Dependent Stress-Protective Effect of 24-Epicastasterone and Its Monosalicylate on Wheat Seedlings in Hyperthermia

The effects of 24-epicastasterone (EC) and its conjugate with the residue of salicylic acid (EC 2-monosalicylate, ECMS) on the heat resistance of wheat seedlings are compared. The treatment of seedlings with ECMS at concentrations of 20 and 50 nM caused a more significant increase in heat resistance as compared to the action of EC, salicylic acid (SA), and a mixture of EC and SA at the indicated concentrations. A transient increase in the content of hydrogen peroxide in seedling roots under the influence of EC and ECMS was observed; in this case, the effect of ECMS was more significant. Seedling treatment with ECMS caused a more notable increase in the activity of antioxidant enzymes (catalase and guaiacol peroxidase) in the roots as compared to the action of EC. The effect of EC and its salicylate on the indicators of the pro-and antioxidant balance in root cell and the heat resistance of seedlings was eliminated via treatment with the antioxidant dimethylthiourea and the NADPH oxidase inhibitor imidazole. A conclusion is made about the ROS-mediated action of the studied compounds on the stress-protective systems of seedling roots. The more significant protective effect of ECMS in comparison with EC may be associated with the gradual release of SA and EC from the conjugate and the functional interaction of the signaling pathways of brassinosteroids and SA.