Plants, Nutrients and Australian Soils

In legumes such as clover, Rhizobium bacteria come into contact with and enter root hairs and adjacent cells by way of an 'infection thread'. Cortical cells of the root divide rapidly and a swelling (nodule) of the root develops within a few days. Vascular bundles of the root grow into the nodule.

The infection thread enters the nodule carrying bacteria with it. Bacteria are released into membranous sacs in the cytoplasm of the nodule cells.

Cross-section of a nodule and an adjoining root. Root nodule with central cells containing numerous bacteroids. These cells are pink in color due to the presence of an oxygen binding molecule similar to our haemoglobin.