Positive chemotaxis of plant growth-promoting rhizobacteria to the ionized form of rutin

Flavonoids are known to perform complex physiological functions in the plant organism. The synthesis of flavonoids, their quantitative and qualitative composition depends on the genotype, age and habitat of the plant. Flavonoids are predominantly synthesized in assimilating organs and then distributed throughout the plant organism. Part of the flavonoids is released through the roots into the rhizosphere. Depending on the chemical structure, flavonoids in the soil can be ionized, oxidized or form covalent adducts with thiol compounds, complexes with metals or ammonium forms of nitrogen.

Rutin (quercetin-3-O-rutinoside), when excreted by plant roots in a slightly alkaline environment, like most flavonols, is partially ionized, acquiring greater mobility in soil solutions. In combination with ammonium nitrogen, rutin actively spreads in the rhizosphere and is recognized by rhizospheric bacteria. Thus, PGPR (plant growth-promoting rhizobacteria) isolated from the seed coat of soybean (Glycine max (L.) Merr.) reveal high sensitivity to rutin-ammonium complexes. Pseudomonas putida strain PPEP2-SEGM-0220 (GenBank: MW255059.1) stimulated the growth of main and lateral roots in soybean seedlings. The sensitivity of this strain to the rutin-ammonium complex on nutrient medium (King's B) was found at a solution concentration of 5 µg/ml. This indicates that the ionized form of rutin is biologically active and performs the function of a selective attractant for symbiotic microorganisms in the rhizosphere. Obviously, isolated PGPRs have molecular mechanisms for recognition of the rutin-ammonium complex. The presence of positive chemotaxis increases the probability of colonization of the plant with the PGPR strains it needs. Thus, the processes of transformation of quercetin-3-O-rutinoside in the soil are extremely important in the formation of plant-microbial systems.