EARLY COLONIZATION OF BARLEY ROOTS BY PSEUDOMONAS-FLUORESCENS STUDIEDBY IMMUNOFLUORESCENCE TECHNIQUE AND CONFOCAL LASER-SCANNING MICROSCOPY

Highly specific polyclonal antibodies against two Pseudomonas fluoresc ens strains (DF57 and Ag1), which differed by approximately 10% of the ir utilizable substrates as tested in Biolog GN plates, were used for in situ labelling of bacterial cells colonizing barley roots grown in sterile soil. By using a confocal laser scanning microscope single bac teria of both strains could be detected on the roots. Seed-inoculated bacteria rapidly colonized the root surface (rhizoplane) by active mig ration; after 1 day the anterior part of the root was densely covered by bacteria occupying the crevices between epidermal root cells. As th e roots became longer, this bacterial population in the rhizoplane for med long strings of closely associated cells. After 7 days, however, t he rhizoplane population of string-forming cells was partially detache d developing a patchy distribution along the root; a separate populati on of cells localized in the slime matrix (mucigel) surrounding the ro ot was well developed at this time. Using two different fluorochromes attached to the antibodies, the two strains could be detected simultan eously in coinoculation experiments. The recordings, however, gave no indications of competition between the two strains during root coloniz ation.