Effect of 24-epibrassinolide on Bradyrhizobium japonicum in pure culture and in symbiosis with Glycine max

Abstract

Brassinosteroids are a group of plant steroid hormones that regulate a wide range of physiological responses, including cell elongation, photomorphogenesis, xylem differentiation, seed germination, etc. It has been proven that these hormones contribute to the formation of legume-rhizobia symbiotic systems. Applied research indicates the potentially complex role of brassinosteroids in the formation of nodules with both positive and negative effects. Therefore, research aimed at studying their role in the processes of symbiosis formation and functioning remains relevant. The aim of the study was to investigate the effect of 24-epibrassinolide on growth indicators of Bradyrhizobium japonicum in pure culture and realization of their nitrogen-fixing potential in symbiosis with soybean plants. It was found that the B. japonicum PC08 strain did not show a pronounced response to the application of concentrations 5 · 10—4, 1 · 10—5 g/L of 24-epibrassinolide.Both positive and negative effects of the tested substance on the growth dynamics this strain were weakly expressed or completely absent. The addition of this phytohormone to the growth medium of the rhizobial strain B. japonicum T21-2 led to stimulation of the growth of rhizobial cells. It was found that 24-epibrassinolide provided an increase in the number of root nodules, regardless of its concentration and the method of application. It had a significant effect on the growth of the root system of soybean plants, while its use as a component of the inoculation suspension in concentration 1 · 10—5 g/L was more effective. As a result of our research, changes in the dynamics of rhizobia growth under the influence of 24-epibrassinolide were revealed. The effect of its application was largely determined by the strain of B. japonicum that we used. We believe that the reaction to the use of 24-epibrassinolide depends on the properties and origin of the strain. The positive effect of 24-epibrasinolide on the number of formed root nodules at the late stages of the formation of the symbiotic apparatus was confirmed. Recorded changes in nitrogen-fixing activity of symbiotic systems under the influence of 24-epibrasinolide indicate that brassinosteroids have an effect on the functioning of root nodules.