Nitrogen Fixation

Nodule Formation and Nitrogen Fixation in Legumes

In general, it is known that legumes need high amounts of Boron. One of the main reasons for this is that Boron plays an important role in nitrogen fixation and related physiological processes. Indeed, the element Boron plays an important role in the nitrogen metabolism of plants, especially legumes. For example, nitrogenase enzyme, which plays the most effective role in the nitrogen fixation process, is very sensitive to boron deficiency conditions and shows a significant decrease in its activity. There are research articles conducted and published on different leguminous plants such as soybean and pea.  

In experiments performed on some cyanobacteria capable of photosynthesis and nitrogen fixation, nitrogenase was found to be strongly affected by Boron application. For example, it has been found that nitrogenase enzyme activity is significantly reduced when bacteria are exposed to boron deficiency for a very short time, such as 2 hours, but photosynthesis or respiration, for example, is not affected. 

It has been reported that the formation and development of nodules where nitrogen fixation takes place on the roots are adversely affected by boron deficiency. There is not enough information about how nitrogenase enzyme and nodule formation is affected by the boron deficiency. However, it is considered that the physical/structural and functional deteriorations on cell walls and cell membranes caused by boron deficiency lead to such problems. Some researchers suggest that the negative effects of boron deficiency on the nitrogenase enzyme are related to Oxygen in the environment because the negative effects of Boron deficiency on the nitrogenase activity do not occur when the environment is anaerobic (without oxygen). Probably, Boron deficiency reduces nitrogenase enzyme activity by causing oxidative stress (increasing the production of toxic O2 radicals). It is known that the nitrogenase enzyme is extremely sensitive to O2 and O2 radicals. Interestingly, increases were found in both nodule formation and nitrogen concentration of plants with the application of Ascorbic acid to plants. 

When nitrogen is sprayed from the leaves to the soybean plant in boron deficiency conditions, increases in nitrate reductase enzyme activity were found in the leaves. Nitrate reductase enzyme activity plays an important role on the nitrogen uptake of the roots on the one hand, and on the protein biosynthesis on the other hand. It has been reported that there is an increase in the protein concentration in the grain of the soybean plant applied foliar boron. The results show that a good Boron nutrition in legumes is important for nitrogen fixation capacity and nitrogen metabolism of plants.