Cytokinin production by some bacteria: Its impact on cell division in cucumber cotyledons

Bacterial strains isolated from rhizosphere of different plants were screened for cytokinin production by developing a simple and rapid bioassay technique. The assay was based on the ability of cytokinin to stimulate greening in etiolated cucumber cotyledons. Isolated bacterial strains were grown on half of 0.6% agar plate for 96 h at 30°C. Etiolated cucumber cotyledons were placed at 2 mm distance from bacterial culture under green light. After initial incubation for 20 h in darkness the plates were exposed to light for three hours. Greater chlorophyll contents were obvious in cotyledons exposed to Bacillus licheniformis Am2, Bacillus subtilis BC1 andPseudomonas aeruginosa E2 strains. Sensitivity of the plate assay was 10-7 M of cytokinin. Cytokinin fractions in bacterial extract (BE) were separated by Thin Layer Chromatography (TLC) and quantified by High Performance Liquid Chromatography (HPLC). Major cytokinin species detected were zeatin and zeatin riboside. Bacterial extract enhanced cell division, fresh weight and cotyledon size in dark as well as light grown cucumber cotyledons against control.   Key words: Bacillus, pseudomonas, cytokinin, cell division, cucumber, cotyledons, Trans-zeatin, HPLC, TLC.