What is the solution to the mystery of plant nitrogen fixation?

As we all know, an important condition for high yield of crops is to have enough fertilizer. When it comes to fertilizers, we can't do without various fertilizers, such as ammonium sulfate, urea, ammonium bicarbonate, human and animal manure and green manure.

It is strange that ordinary crops can't grow well on barren land, while leguminous plants can grow well without chemical fertilizer. Why? The secret lies in the roots of legumes.

If you carefully observe the roots of leguminous plants, you will find many small protrusions, like small tumors, so they are called "nodules" by scientists. Nodules look ordinary, and some fishy "red water" will flow out after crushing. However, this "red water" is not common. If you put it under a microscope, you can see many tiny creatures moving in the red juice, some like sticks and some like balls. These little guys are famous rhizobia.

We know that the air contains a lot of nitrogen, which is an indispensable and important nutrient element for plant growth. However, nitrogen in the air is free and cannot be directly absorbed by plants. Only by changing the free molecular nitrogen in the air into nitrogen-containing compounds can it be absorbed and utilized by plants. To do all this, nitrogen-fixing microorganisms are needed, and rhizobia of leguminous plants are an important member.

For many years, scientists have been exploring the mystery of nitrogen fixation in leguminous plants and trying to solve the mystery of nitrogen fixation in rhizobia. Because this research is so important, if successful, it will mean saving tens or even hundreds of billions of dollars of artificial nitrogen fertilizer every year. William trager, a famous American biological expert, made a surprising data after careful calculation: the number of leguminous plants fixing nitrogen in the soil reaches 90 million tons every year in the world.

The research on nitrogen fixation ability of leguminous plants can be traced back to 1838. French agricultural chemist Posinger Root first discovered that leguminous plants can fix nitrogen in the atmosphere in a molecular state. 1866, Russian scholar voronin discovered that rhizobia of leguminous plants contained microorganisms, and pointed out that the formation of nodules was the result of microorganisms invading the roots of plants. 1888, Dutch scientist Beylink obtained the pure strain of rhizobia for the first time by isolation. Since then, people have gradually uncovered the outermost layer of the mystery of plant nitrogen fixation.

Scientists have found that rhizobia do not have the function of nitrogen fixation when they live alone in soil. Only when the seeds of leguminous plants are sown in the soil, after the young roots are formed, the secretion of the roots attracts rhizobia, so that rhizobia can invade the internal tissues of the roots through the root hairs and propagate there, so that the roots expand and form nodules. At this time, rhizobia in nodules have formed a special relationship with leguminous plants, and rhizobia began to play the role of nitrogen fixation and supply plants.

Scientists also found that there are many kinds of rhizobia, and each rhizobia can only form nodules in the roots of one or several plants. For example, rhizobia can only form nodules in the roots of peas and broad beans; Alfalfa rhizobia can only form nodules in the roots of alfalfa and cauliflower; Cowpea rhizobia can only form nodules in the roots of cowpea, mung bean and peanut; However, rhizobia of Astragalus sinicus can only form nodules in the roots of Astragalus sinicus.

After years of research and exploration, scientists have more and more understanding of the nitrogen fixation mechanism of rhizobia, but there are also more and more problems and puzzles. When people clearly understand that microorganisms will change their shape and become Proteus after entering the root tissue of plants, the main question before scientists is: Can Proteus reproduce? How do they reproduce? Can they make rhizobia complete their life cycle one after another?

Scientists have different views on these annoying problems. Many scholars believe that in the last stage of Proteus' existence, their plant owners violated the principle of * * * and digested their students. If the next generation of plants want to be infected by rhizobia, they must reproduce through new bacteria in the soil. However, some scholars believe that not all bacteria will become Proteus, and maybe a few are indigestible. Later, mishkin, an academician of the former Soviet Academy of Sciences, and his collaborators found that small round cells-like spores-would form inside Proteus, so he speculated that rhizobia would stay in the soil in the form of spores to avoid extinction.

Old arguments continue, and new problems follow. In the process of studying plant nitrogen fixation, scientists are extremely concerned about whether rhizobia can also carry out nitrogen fixation after leaving plants. This is an idea to break the traditional concept, because according to the previous concept, rhizobia can only absorb nitrogen from the air and fix nitrogen by combining with leguminous plants. That is to say, rhizobia live independently in the soil for most of their lives. Like other microorganisms in the soil, they also rely on absorbing ready-made organic matter around them to survive, but they cannot fix nitrogen in the air. Rhizobia can live for decades from generation to generation, waiting to meet the right plants. Once a good opportunity is met, rhizobia will gladly bid farewell to the living environment of soil and enter the roots of plants, so that the root tissue will proliferate and become tumor-like. At this time, rhizobia acquired a new wonderful characteristic-nitrogen fixation ability.

Scientists have known that it is the nitrogenase in plant rhizobia that makes rhizobia produce nitrogen-fixing ability, but the question is, must nitrogenase be produced with the cooperation of plants and rhizobia?