Nodule cosmos

Symbiosis between a Japanese bird’s-foot trefoil and nodule bacteria

Legumes, such as bird’s-foot trefoil, can form a root nodule symbiosis with nitrogen-fixing bacteria. In order to host the bacteria and provide them with optimal conditions for nitrogen fixation, plants form new organs, so-called root nodules. On the root of a Japanese bird’s-foot trefoil (Lotus japonicus) you can see such a nodule that has been infected by bacteria. The bacteria are housed within the plant cell in demarcated spaces, so-called symbiosomes. There, they fix nitrogen and in return receive sugar from the plant, which it obtains through photosynthesis. In this image, the bacteria are coloured red by a fluorescent protein. You can clearly see how densely the nodule is colonised by bacteria.