Résumé
Crotalaria are plants of the Fabaceae family whose nodulation characteristics have been little explored despite therecent discovery of their unexpected ability to be efficiently nodulated in symbiosis with bacteria of the genusMethylobacterium. It has been shown that methylotrophy plays a key role in this unusual symbiotic system, as it isexpressed within the nodule and as non-methylotroph mutants had a depleting effect on plant growth response.Within the nodule, Methylobacterium is thus able to obtain carbon both from host plant photosynthesis and frommethylotrophy. In this context, the aim of the present study was to show the histological and cytological impacts ofboth symbiotic and methylotrophic metabolism within Crotalaria podocarpa nodules. It was established that ifCrotalaria nodules are multilobed, each lobe has the morphology of indeterminate nodules but with a differentanatomy; that is, without root hair infection or infection threads. In the fixation zone, bacteroids display a sphericalshape and there is no uninfected cell. Crotalaria nodulation by Methylobacterium displayed some very unusualcharacteristics such as starch storage within bacteroid-filled cells of the fixation zone and also the complete lysis ofapical nodular tissues (where bacteria have a free-living shape and express methylotrophy). This lysis could possiblyreflect the bacterial degradation of plant wall pectins through bacterial pectin methyl esterases, thus producingmethanol as a substrate, allowing bacterial multiplication before release from the nodule.