GENE-EXPRESSION IN INEFFECTIVE ACTINORHIZAL NODULES OF ALNUS-GLUTINOSA

Several Frankia strains have been shown to induce ineffective, i.e. no n-nitrogen fixing nodules, sometimes in a host-plant dependent manner. Previous studies have demonstrated that the resistance to nodulation of Alnus glutinosa by ineffective Frankia strains is genetically deter mined. In this study, ineffective nodules induced on susceptible Alnus glutinosa clones by soil suspensions from a local swamp were analysed cytologically, Comparisons with effective nodules showed that ineffec tive nodules contain higher amounts of polyphenols than effective nodu les, indicating a plant defense reaction. Polyphenols were found even in the infected cortical cells. In situ hybridization with a Frankia a ntisense 16S rRNA probe showed that Frankia is degraded at an early st age of development of infected cells. The mRNAs of two plant genes, ag 12 and ag13, which had been found to be expressed in the infected cell s of effective nodules, were localized in ineffective nodules. Their e xpression patterns seemed to be analogous in both types of nodules.