It is known that in the root zone of plants rhizobacteria able to synthesize a wide range of biologically active compounds, including compounds of phytohormonal nature. Previously it was found the ability of nitrogen-fixing symbiotic bacteria Bradyrhizobiumjaponicum synthesize auxins, cytokinins and abscisic acid . It is known that phytohormones with growth stimulation activity (gibberellins) have wide spectrum of influence on physiological processes in plants. Gibberellins cause lengthening stems of plants, which is based on the cell spreading and increased mitotic activity.
The aim of the work was to study the synthesis of gibberellic extracellular compounds by strains of nitrogen-fixing symbiotic bacteria B. japonicum.
The objectsofresearchwereB. japonicum strains, which differ in their symbiotic efficiency: highlyeffective strains UCM В-6018, UCM В-6023, UCM В-6035, UCM В-6036 and ineffective strains 21110, 604k.
All B. japonicumstrains were grown in a liquid yeast extract mannitol medium in periodic conditions. Phytohormones with gibberellic activity were isolated with ethyl acetate in the ratio 1:1 (v/v) at pH 2.5. The obtained extracts were evaporated at 40-45 °C. Dry residue was dissolved in ethanol and used for physical and chemical analysis of phytohormones.
To determine gibberellic activity we used hypocotyls of cucumber grade Fenix seedlings by technique Brian’s and Lemming’s bioassay in the modification by Ahnistikova. After germination of cucumber seeds during 3-4 days (temperature 27 °C) hypocotyls with length 2.0 ± 0.2 cm were selected. Hypocotyls were placed in Petri dishes with aliquots of aqueous solutions of extracts at dilutions 1:400, 1:500 and 1:600. After incubation for 1-2 days at 27 °C elongation of hypocotyls was measured and it was compared to controls (treatment with distilled water and a solution gibberellic acid (GA3) at a concentration of 10-5 M).
The treatment of cucumbers grade Fenix seedlings with extracts of gibberellic nature compounds was accompanied by stimulation hypocotyls elongation. The largest increase in the length of cucumber hypocotyls was observed for the extract of ineffective strain B. japonicum 21110. The increase not only didn't concede to the reference sample of gibberellic acid (GA3) but exceeded its effect on 16.5%, 10.3% and 22.7% in dilutions 1:400, 1:500 and 1:600 respectively. Slightly lower growth rates were observed for the extracts obtained from the supernatant culture liquid after cultivation of other strains. However, it is worth to mention that the most effective dilution appeared to be 1:400. In this dilution almost every strain showed the highest stimulation effect. B. japonicum UCM В-6018 and B. japonicum 604k showed the highest stimulation in dilutions 1:600 and 1:500 respectively. Stimulation percentage of the strains was almost equal to the reference sample of GA3 under these dilutions.
To sum up, we can affirm the presence of compounds with gibberellic activity in supernatant culture liquid of studied bacteria B. japonicum. Besides, there is grounds to talk about possible prospects of using these strains for seeds growing stimulation and increasing of plants productivity as preparations with gibberellic stimulation activity.
1.Dragovoz I.V. Phytohormones synthesis by Bradyrhizobiumjaponicumstrains with different symbiotic effectiveness / I.V. Dragovoz, N.O. Leonova, G.O.Iutynska// Mikrobiol. J. -2011. - Vol. 73, № 4. - P. 29-35. (In Russian).