EARLY INTERACTIONS BETWEEN ALNUS-GLUTINOSA AND FRANKIA STRAIN ARI3 - PRODUCTION AND SPECIFICITY OF ROOT HAIR DEFORMATION FACTOR(S)

Actinomycetes from the genus Frankia are able to form symbiotic associ ations with more than 200 different species of woody angiosperms, so c alled actinorhizal plants. Many actinorhizal plants are infected via d eformed root hairs. Factor(s) eliciting root hair deformation in actin orhizal symbioses have been found to be released into the culture medi um, but the factor(s) has (hav) not yet been characterized. In the pre sent work, we describe the constitutive production of factor(s) by Fra nkia strain ArI3 causing root hair deformation on Alnus glutinosa. Def ormation was detected after 4-5 h of incubation with both Frankia cult ures and their cell-free culture filtrates. When culture filtrate was used, deformation was concentration dependent. A contact time of 2 min between culture filtrate and host roots was sufficient to induce subs equent root hair deformation. No root hair deformation on A. glutinosa could be detected with purified Nod factors from Rhizobium meliloti o r R. leguminosarum biovar viciae. No correlation was found between Fra nkia strains belonging to different host specificity groups and their ability to deform root hairs on A. glutinosa. However, strains not abl e to deform root hairs on A. glutinosa were also unable to nodulate.