Transport of bacterial cytokinins to shoot and their influence on growth of barley plants

One important mechanism underlying the promotive action of rhizosphere bacteria on plants is their ability to produce plant hormones, particularly cytokinins. Cytokinin must be delivered from the roots to stimulate plant growth and exert beneficial effects on the shoots. This work aimed to study the transport of bacterial cytokinins in barley plants. We studied the effects of cytokinin-producing bacteria on the growth, cytokinin content, and expression of the HvABCG gene, a homolog of the rice OsABCG18 and Arabidopsis AtABCG14 genes encoding transporters of these hormones. Rhizosphere of 3-days-old barley seedlings were inoculated with Bacillus subtilis IB-22, and cytokinins were immunoassayed on the sixth day after bacterial treatment. On day 11, leaf growth stimulation was detected under the bacterial treatment, indicating that bacterial cytokinins affect shoot performance. This hypothesis was confirmed by a 1.5 increase in zeatin riboside levels registered in the shoots of bacteria-treated plants. Estimating the expression of the HvABCG gene showed its upregulation in the roots of bacteria-treated plants, suggesting the involvement of this transporter in the delivery of cytokinins to the shoots.