nodulating

Nodulating refers to the development of nodules on the roots (and in some cases stems) of certain plants as part of a symbiotic relationship with nitrogen-fixing bacteria. The term is most commonly applied to legumes, which form nodules with rhizobial bacteria, though some actinorhizal plants form nodules with Frankia bacteria. Nodulation results in specialized plant organs that host bacteria capable of converting atmospheric nitrogen into ammonia, a form usable by the plant, thereby contributing to soil fertility and reducing the need for synthetic fertilizers.

The nodulation process begins when legume roots release flavonoids that attract rhizobia. In response, rhizobia produce Nod factors, signaling molecules that are recognized by plant receptor kinases. This recognition triggers a signaling cascade that causes root hair curling, infection thread formation, and cortical cell divisions that give rise to nodule primordia. Bacteria travel through the infection threads into developing nodules, where they differentiate into nitrogen-fixing bacteroids within plant-derived cells. The nodules contain leghemoglobin, a protein that regulates oxygen supply to the nitrogenase enzyme, preserving nitrogen fixation while providing enough oxygen for plant respiration. Fixed nitrogen, primarily as ammonium, is transported to the plant, supporting growth.

Nodules vary in structure: indeterminate nodules have a persistent growing tip, while determinate nodules cease growth after formation. Nodulation is a tightly regulated process influenced by plant and bacterial genes as well as environmental factors, including phosphate and molybdenum availability, soil pH, and microbial compatibility. Regulation mechanisms, such as autoregulation of nodulation, limit the number of nodules to balance carbon expenditure with nitrogen gain.

Nodulating has significant agricultural and ecological importance, enhancing legume productivity and contributing to sustainable soil nitrogen without excessive fertilizer inputs.