Forced association between higher plant and bacterial cells in vitro

SYMBIOTIC associations with microorganisms enable many plant species to utilise molecular nitrogen 1–3 . In vitro systems have been developed to study some of these natural associations 4–7 , and here we have attempted to define an experimental system for investigating the possibility of extending the nitrogen-fixing symbiosis to additional crop species. We used tissue culture techniques to force an association between the free-living nitrogen-fixing bacterium, Azotobacter vinelandii and cells of a carrot, Daucus carota cv. Danver's Half Long. The resulting composite callus proliferates slowly on a defined synthetic medium lacking combined nitrogen. In these conditions carrot cells which have not formed an association with Azotobacter are unable to survive.