Essential metals improve nitrogen production
Nitrogen fixation occurs when plants convert atmospheric nitrogen to an inorganic form that can be used to construct plant building blocks like DNA and amino acids. Legumes like beans and peas fix nitrogen with the help of bacteria that live in a special nodule within the plant's root. These symbiotic bacteria convert atmospheric nitrogen to ammonia using specialised enzymes that require metallic elements to function correctly. Because they fix nitrogen, legumes are used in crop rotation cycles to enrich soils in nitrogen and to reduce the need for fertilisers. Since this process depends on precious metals in soils, metal deficiency has a severe impact on crop yields. For the EU-funded MENOMED (Metal homeostasis in nodulated Medicago truncatula) project, researchers used a model legume to study how plants regulate metals to ensure nodules can still fix nitrogen even when metals are scarce. To see whether plants redistribute metals from other parts of the plant, researchers determined the path that metals follow from the soil to the nodule. They found that iron, one essential metal required by nitrogen-fixing enzymes, is released by the plants into a bacteria-packed area of the nodule. They also discovered numerous transporter proteins that deliver metals to this area of the nodule, known as the infection zone. This ensures that metals are available at the same time and place that proteins responsible for fixing nitrogen are being made. Understanding how nitrogen fixation is regulated in the nodule and which elements are involved may improve productivity by increasing nitrogen assimilation. This may in turn reduce nitrogen fertiliser applications, which cost billions of euros per year and contribute to 15 % of global greenhouse emissions.
Keywords
Metals, nitrogen, legumes, soils, nitrate, nitrogen fixation, symbiotic bacteria, transporter proteins
