Hormone production by micro-organisms selected as antagonists of pathogenic fungi and the effect of their introduction into soil on hormone content and growth of lettuce plants were studied. Hormones in bacterial cultural media and in plant extracts were immunopurified and assayed using specific antibodies to indolyl-3-acetic acid (IAA), abscisic acid (ABA), and different cytokinins (zeatin riboside (ZR), dihydrozeatinriboside (DHZR) and isopentenyladenosine (iPA)). ZR was shown to be the main cytokinin present in bacterial cultural media as a complex with a high molecular weight component. Inoculation of lettuce plants with bacteria increased the cytokinin content of both shoots and roots. Accumulation of zeatin and its riboside was greatest in roots shortly 2 days after inoculation, when their content was 10 times higher than in control. Changes in the content of other hormones (ABA and IAA) were observed at the end of experiments only. Accumulation of cytokinins in inoculated lettuce plants was associated with an increase in plant shoot and root weight of approximately 30% over 8 days.

Cytokinins can promote stomatal opening, stimulate shoot growth and decrease root growth. When soil is drying, natural cytokinin concentrations decrease in association with stomatal closure and a redirection of growth away from the shoots to the roots. We asked if decreased cytokinin concentrations mediate these adaptive responses by lessening water loss and promoting root growth thereby favouring exploration for soil water. Our approach was to follow the consequences for 12-d-old lettuce seedlings of inoculating the growing medium with cytokininproducing bacteria under conditions of water sufficiency and deficit. Inoculation increased shoot cytokinins as assessed by immunoassay and mass spectrometry. Inoculation also promoted the accumulation of shoot mass and shortened roots while having a smaller effect on root mass. Inoculation did not raise stomatal conductance. The possible promoting effect of these cytokinins on stomatal conductance was seemingly hampered by increases in shoot ABA that inoculation also induced. Inoculation lowered root/shoot ratios by stimulating shoot growth. The effect was greater in non-droughted plants but remained sufficiently strong for shoot mass of inoculated droughted plants to exceed that of well-watered non-inoculated plants. We conclude that compensating for the loss of natural cytokinins in droughted plants interferes with the suppression of shoot growth and the enhancement of root elongation normally seen in droughted plants.

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Bacterization of the seeds of spring durum wheat with the strains of gram-positive aerobic spore-forming bacteria Bacillus subtilis IB-21 and B. subtilis IB-22 and gram-negative bacteria Advenella kashmirensis IB-К1and Pseudomonas extremaustralis IB-К13-1А was performed to study its effect on the productivity of plants, their hormonal content and rhizosphere phosphorus (P) status in the field experiments. A. kashmirensis IB-К1 andP. extremaustralis IB-К13-1А were the most capable of mobilizing hardly soluble phosphates in vitro, while P. extremaustralis IB-К13-1А produced the greatest concentration of auxins. All the studied strains successfully colonized the plant root system, the level of colonization detected during the second leaf stage being the highest in the case of A. kashmirensis IB-К1 and B. subtilis IB-22. Seed treatment with all the tested bacterial species resulted in an increase in phosphate mobility in the rhizosphere. Auxin content in wheat roots was increased by bacterization of seeds with P. extremaustralis IB-К13-1 and B. subtilis IB-22. The maximum increase in components of wheat crop yield (the mass of grains in the main and axillary spikes) was detected during 3 vegetative periods (2016, 2017 and 2018) in the case of seed treatment with the strains inducing a significant increase in auxin content in the roots of the treated plants related to either the highest bacterial capacity of producing this hormone in vitro (in the case of P. extremaustralis IB-К13-1А) or root colonization (in the case of B. subtilis IB-22).