Synthesis of Tetraesters of Indolyl-3-acetic Acid with 24-Epibrassinosteroids and Their Influence on the Initial Growth of Wheat Plants

Objective: The aim of this work was to synthesize 2,3,22,23-tetraindolyl-3-acetoxy derivatives of 24-epibrassinosteroids, study their growth-regulating activity at the initial stage of spring wheat development and influence on the content of endogenous brassinosteroids during the growth of wheat plants. It has been shown that brassinosteroid tetraesters of indolyl-3-acetic acid exhibit phytogrowth-regulating activity in the early stages of wheat plant growth. Methods: By treating 24-epibrassinosteroids with indolyl-3-acetic acid (IAA) anhydride in dioxane in the presence of DMAP, their 2,3,22,23-tetra-(3′-indolylacetoxy) derivatives were obtained. Quantitative analysis of endogenous BS content was performed by ELISA using previously developed test systems for the determination of 24-epibrassinosteroids, 28-homobrassinosteroids and brassinosteroids of the brassinolide group. Results and Discussion: The synthesized brassinosteroid tetraesters with IAA have a growth-stimulating effect at the initial stage of wheat plant development. Exogenous treatment of wheat plants with brassinosteroid solutions and their esters with IAA changes the brassinosteroid profile at the early stages of development. A decrease in the content of BS of the brassinolide group and 28-homobrassinosteroids 14 days after exogenous treatment confirms the fact that brassinosteroids participate in the processes of regulation of their biosynthesis, thus maintaining the steroid-hormonal balance for optimal growth and development of plants. Conclusions: For the first time, tetraesters of IAA and 24-epibrassinosteroids were synthesized. Primary screening of the obtained compounds in laboratory tests on wheat plants showed growth-stimulating concentration-dependent activity. Changes in the steroid-hormonal balance of BS in vegetative plants when treated with 24-epibrassinosteroids or BS tetraesters with IAA may indicate their participation in the processes of biosynthesis regulation. The obtained derivatives are promising for more in-depth study, primarily for investigating their effectiveness in field experiments.