Root form a cellulosic tube (the infection

Root nodule
formation is a complex process that results in nitrogen fixing symbiosis. The plant
root releases nutrients that attract rhizobia and other bacteria. Symbiosis
first takes place when rhizobia attach to the surface of legume root hairs,
rhicadhesin is present on the surface of specific rhizobium species. Carbohydrates
containing lectins are important plant cell surface receptors (Bothe et al,
2007). Following binding, the root hair curls as the result of nod factors which
migrate to the plant cell nucleus and influence transcriptions of genes needed
for the symbiotic relation. Following curling the bacteria enter the root hair
and induce the plant to form a cellulosic tube (the infection thread) which
spreads down the root hair and into adjoining cells. Plant cells become
infected by movement of the bacteria through the infection thread and start to
divide in response to nod factors from the rhizobia. The rhizobia multiply rapidly
in the plant cells and are transformed into misshapen structures called
bacteroids, bacteroids become surrounded by plant cell membrane to form
structures called symbiosomes, this stage is when nitrogen fixation can begin (Mortier et al, 2012).