M. G. Sokolova

The effects of pea (Pisum sativum L.) seedling inoculation with nodule bacteria (Rhizobium leguminosarum bv. viceae) and hypothermia on the content of cytokinins (Ck) in seedling roots during 8 days after external factor action were studied. As soon as a day after inoculation with Rh. leguninosarum, the content of Ck in the seedling roots increased, especially in the root zone most susceptible to infection (0–20 mm from the tip); this not only affected growth of the whole roots but also determined the initiation of nodule primordia. Hypothermia (8°C) reduced the content of CK as soon as in a day. After 5 and 8 days of hypothermia, the content of Ck in inoculated plants was approximately twice higher than in non-inoculated plant roots.

New strains of rhizosphere microorganisms Azotobacter chroococcum Az d10, Bacillus megaterium Pl-04, and Bacillus mucilaginosus B-1574 were found to be able to synthesize cytokinins (CKs) and indolylacetic acid (IAA). Three forms of CKs—dihydrozeatin riboside, isopentenyl adenosine, and trans-zeatin riboside—were identified, whose ratio was different in the three bacterial cultures. Inoculation of cucumber (Cucumis sativus L.) plants increased the content of CKs and IAA in them by 35.6 and 21.3%, respectively, and also stimulated seed germination and increased the growth rate, the biomass of shoots, the number of lateral roots, and the root hair area, which ensured better plant nutrition. The IAA/CKs ratio shifted during bacterization towards CKs due to increase in the content of riboside forms, which apparently caused growth stimulation.