Abstract
Bacteria of the genus Azospirillum live in association with the Graminae. Azospirillum has a growth-promoting effect due to nitrogen-fixation, phytohormone production and improved water household of the plant. Azospirillum is able to attach to plant roots (Umali-Garcia et al. 1980) and A. brasilense Sp245 can even invade into the root cortex. In plant bacteria interactions, signalling is an important factor. There are different signal molecules known in other microbe-plant interactions: β 1–2 glucans in the interaction of Agrobacterium and Rhizobium for respectively tumor-formation and nodule-induction; hepta-saccharides which act as elicitors for the plant-defense mechanisms against plant pathogens; extracellular polysaccharides (EPS) necessary for the formation of nitrogen-fixing nodules on legumes by Rhizobium. The production of EPS by Azospirillum was shown by the fluorescent dye Calcofluor. In the F. A. Janssens Memorial Laboratory for Genetics, recent interest is focussed on the genetics of the synthesis of this EPS by Azospirillum. Tn5 induced A. brasilense mutants that are are affected in Calcofluor fluorescence have already been isolated (Michiels et al., 1988a; 1990). Some A. brasilense genes are able to correct R. meliloti exo mutations. In this way, the R. meliloti exoB, exoC, exoG, exoM, exoN, exoP and exoK mutants have been genetically complemented by A. brasilense DNA. The exoB, exoC1 and exoM correcting loci are located on the 90 MDa plasmid of A. brasilense Sp7 (Michiels et al., 1988b; Marc Eyers, personal communication), whereas the exoC2, exoG, exoK, exoN and exoP correcting loci are located on the chromosome (Marc Eyers, personal communicaton). The A. brasilense exoB en exoC1 mutants have been constructed by marker-exchange (Michiels et al. 1988b).
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De Troch, P., Philip-Hollingsworth, S., Orgambide, G., Michiels, K., Vanderleyden, J., Dazzo, F.B. (1991). Analysis of extracellular polysaccharides of Azospirillum brasilense . In: Polsinelli, M., Materassi, R., Vincenzini, M. (eds) Nitrogen Fixation. Developments in Plant and Soil Sciences, vol 48. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-3486-6_66
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