ABSTRACT
Investigations of microbial production of cytokinins have concentrated on plant pathogens, with little emphasis placed on the quantification of cytokinins produced by nonpathogenic rhizobacteria other than rhizobia. Conventional procedures for extraction and purification from plant tissues and microbial cells include homogenization, extraction with organic solvents, purification with binding resins, separation by chromatography, and bioassays for the measurement of bioactivity. A preliminary cleanup of plant or microbial extracts to remove large quantities of impurities can be accomplished by ion exchange. Production of soil metabolites is often directly linked to substrate availability. Primary sources would include plant and animal exudates and decomposing residues. Concentrations of all the plant hormones were higher in the rhizosphere, probably as a consequence of the increased microbial populations or possibly of accelerated metabolism in the presence of root exudates. The inoculation of cytokinin-producing nonpathogenic organisms has been reported to affect positive plant growth and yields.
