Résumé
Some leguminous species of the genus Aeschynomene
are specifically stem-nodulated by photosynthetic bradyrhizobia. To
study the effect of bacterial photosynthesis during symbiosis, we
generated a photosynthesis-negative mutant of the
Bradyrhizobium sp. strain ORS278 symbiont of
Aeschynomene sensitiva. The presence of a functional
photosynthetic unit in bacteroids and the high expression of the
photosynthetic genes observed in stem nodules demonstrate that the
bacteria are photosynthetically active during stem symbiosis. Stem
inoculation by the photosynthetic mutant gave a 50% decrease in
stem-nodule number, which reduced nitrogen fixation activity and plant
growth in the same proportion. These results indicate an important role
of bacterial photosynthesis in the efficiency of stem nodulation.