Nitrogen fixation: relationship between plants and bacteria (Part 1)

The air is almost a joke. Nothing can resist oxygen but 78% of the air is nitrogen. Nitrogen is often the source of life on earth and is a source of nutrition that determines how much things grow, where they grow. Yet large amounts of nitrogen passing through the lungs or leaves are not helpful to plants and animals: one of the most valuable resources of life is wasted through every breath.

Nitrogen floating in the air in a double atomic form (N ₂ ) is locked together with chemicals through a straight triple bond. Although it is very necessary for this element, the living organism is sufficiently complex when cells have the nucleus - paramecia, potatoes or people are the same - no natural remedies can break that connection. . This is the point where humankind is overtaken by mediocre creatures. 'Simple' forms of life , such as floating cyanobacteria or lurking rhizobia bacteria in the soil, can disrupt this association. This feat, called nitrogen fixing, turns N ₂ into an easier-to-use ammonia form.

Since 1920, Haber-Bosch industrial measures have helped people to separate this connection, as long as there is an energy source that can raise the temperature to 400 or 500 ^° C and a pressure of 200 atmospheres. Yet the scum layer on the surface of the lake can fix nitrogen at room temperature and normal atmospheric pressure.

Legumes and legumes are capable of producing nitrogen from bacteria that are able to break down N2's triple bond at room temperature.In recent decades, scientists have been investigating ways to bring those capabilities into crops.(Photo: iStockphoto)

Certain plants have more neat solutions. By themselves, soybeans, beans, alder and other species, can fix nitrogen better than anyone. In fact, they attract the migrating bacteria and help them do the task.

In a complex, cross-border society like human society, bacteria and plants exchange signals and tests of chemical goodwill until the bacteria migrate stably, usually in niches. or special protrusions of plants, and start fixing nitrogen. With the help of these friends, the plants can get fertilizer from the air.

This is enough for people to envy soybeans. Fertilizer production through Haber-Bosch method for crops consumes tremendous energy. And when energy costs are rising, not to mention burning fossil energy increases greenhouse gas emissions, and a rapidly growing global population requires more food. Only for a third of the world's population, more food means more artificial fertilizers. Things will be simpler if food can use nitrogen from N ₂ in the air.

Allan Downie, of the John Innes Center in Norwich, England, authored a recent article on plant-microbial signaling in the Annual Review of Plant Biology, saying 'People always ask me when we can produce self-fixing nitrogen flour '. Downie said things weren't that simple. He began studying nitrogen fixation during the 1980s and found a long way ahead.

The good news is that science is accelerating. Researching both plants and their bacteria has discovered new, unexpected diversity in nitrogen fixation and gives scientists new partnerships to find clues. operating mechanism. Scientists are also adding knowledge about how legumes use a special chemical list to find and negotiate with potential bacterial 'workers' . Science is looking to re-learn this process, tracking each of its nuances. Even when the teacher here is just small dots in the ground.

Species of nitrogen fixing bacteria

According to David Dalton of Reed University in Portland, Oregon, the power lies in those little dots. Some species, such as cyanbacteria, float in the ocean and process many nitrogen to the point that they are recognized as the main source of ocean chemistry.

Most of the nitrogen in the Douglas old pine forest in the Pacific Northwest may stem from Nostoc cyanbacteria. Some Lobaria lichen species, including Nostoc, are lush, and after 80 years, huge colonies can be established up to the top of the tree. Dalton likened 'Like people pouring a train full of lettuce.'

Other nitrogen fixing species establish loose relationships with plants when settling near roots or moving into tissues without any special shelter. One of the most famous species, now known as Gluconacetobacter diazotrophicus, appears in sugarcane in Brazil in 1988. It belongs to a group of bacteria known to produce acetone acid. But under the right conditions, this species produces enough nitrogen to help the sugarcane grow.

Plants themselves cannot use nitrogen in the air, but they can rely on bacteria to make nitrogen processing gates in root nodules.(Photo: W. Eberhart, Getty Images)

However, the tightest relationships include more specialized structures, such as individual tissues in the tree. The cycads that Dalton describes are like 'dwarf palms' that grow tumors as shelter for cyanobacteria. And a rather strange flowering plant, Gunnera, accepts cyanobacteria bags in the roots. Just cut a piece of root Gunnera just below one of its umbrella-sized leaves, we will see green spots.

Textbooks also include legumes in a nitrogen fixation scheme, but the Frankia bacteria produce small nodules in non-legume plants, such as alder and apricot trees. These 'extremely bony' nitrogen-fixing species live in nodules on the roots.

The most famous plant-bacteria arrangement occurs between bacteria and legumes. Each new recruiting plant forces its workforce, and the bacteria that enter the tiny roots of the plant later become nitrogenous plants that look like pale pink beans. Pink is caused by plant hemoglobin, a relative of the oxygen transport molecule in mammalian blood.

'Violent explosion' is the word that John Howieson, Murdoch University in Australia, described the discovery of numerous species of nitrogen-fixing bacteria in beanstalks in recent years. Biologists know that many microorganisms appear inside the nodules but there is no way to guarantee the separation of fixed bacteria and disguised bacteria.

For more than 100 years, biologists have recorded nodules that only form with bacteria belonging to the alpha branch of the Proteobacteria group, especially the bacteria in the Rhizobiaceae family. However, starting in 2000, researchers discovered nododes in a completely new branch called beta. The first group, a member of the Burkholderia family, was discovered nitrogen fixing for mimosa plants in Brazil.

'We are accustomed to boring gray, milky white nests and now these pink nests appear.' Howieson's collection appears with nitrogen-fixing bacteria including 'strange, fast-growing, pink fast-growing things' as well as 'unnamed thin orange.'

Another expert on the nitrogen fixation note, Janet Sprent of the University of Dundee in Scotland, recalls a much simpler systemization.'A century ago things were much more orderly, and now we are going into a mess.'

Sprent points out that scientists have not even begun to survey many tropical plants, especially legumes, which probably contain new nitrogen fixing bacteria.

(Part 2)