Bean nodules

Photo competition: 1st place in the category ‘Symbiosis’

The photograph shows small nodules on a bean root. Legumes can form a symbiotic relationship with nitrogen-fixing bacteria (rhizobia). The plants form root nodules to accommodate the bacteria and provide them with optimal conditions for nitrogen fixation. The root nodules were sliced lengthwise using a razor blade. The red colour in the centre indicates the presence of leghaemoglobin, an oxygen-binding and iron-containing protein. It is similar to human haemoglobin, which colours our blood red. The main task of leghaemoglobin is to create an oxygen-free environment in the nodules, as the nitrogen-fixing enzyme, nitrogenase, is sensitive to oxygen. The picture was taken during a guided photography tour in the Botanical Garden Munich-Nymphenburg.