Evidence from inhibitor studies that the endophyte synthesises nitrogenase in the root nodules of Alnus glutinosa L. Gaertn.

Nitrogenase activity (acetylene reduction assay) in the nodulated non-leguminous angiosperm Alnus glutinosa is inhibited within minutes when plants are exposed to a gas phase containing 90% oxygen On returning the plants to air, nitrogenase activity recovers within a few hours, both in the presence of cycloheximide, which inhibits protein synthesis on 80 S (eukaryotic) ribosomes, and in the absence of inhibitor. When chloramphenicol, which inhibits protein synthesis on 70 S (prokaryotic) ribosomes, is added instead of cycloheximide, recovery from oxygen inhibition does not occur, or occurs only slowly. The effects of chloramphenicol are specific to the D-threo-isomer which indicates a direct inhibition of protein synthesis. Erythromycin has a similar effect to chloramphenicol. Protein biosynthesis in non-nodulated roots is inhibited by cycloheximide but not by chloramphenicol. The results are interpreted as evidence that the nitrogenase within Alnus glutinosa root nodules is synthesised by the microbial symbiont.