An account of the Nitrogen cycle in plants
...thin the root nodules of leguminous plants for example rhizobium. This conversion however, requires nitrogenase which is an enzyme inhibited by the presence of oxygen and the input of large amounts of energy. These two requirements present a conflict as rhizobium requires oxygen for respiration to produce enrgey yet the oxygen inhibits the nitrogenase activity. The problem is solved by the root nodules producing leghaemoglobin, a protein with a high affinity for oxygen. The leghaemoglobin releases oxygen in a controlled manner for use in respiration and prevents the inhibition of nitrogenase at the same time. Another step is nitrification which is a two stepped process. Although plants can obtain ammonium directly most is converted to nitrate by soil bacteria. In stage one the ammonium is oxidised to Nitrite by Nitrosomonas bacteria, but nitrites are insoluble so are not accessible to higher plants so a second conversion occurs. In step two the nitrite ions are converted to nitrate by Nitrobacter bacteria, this is advantageous to the plant because nitrates are highly soluble and are a major source of nitrogen. Another process in the nitrogen cycle is assimilation. This is the uptake of nitrates and/or ammonioum by primary producers and their incorporation into proteins or nucleic acids. Ammonification is another step and this is t...