Nitrogen fixation: relationship between plants and bacteria (Part 2)

Learn the collaborative process of plants - bacteria

For plants, allowing symbiotic bacteria is a risky thing. Guests must know to keep themselves from growing out of control, destroying tree structures or interfering with chemical mechanisms. In return, species of bacteria have the opportunity to not be rebel owners - food supply - rebellion and establish defense mechanisms for them. So researchers are discovering the exchange signals that make up the deal.

Bruce Hungate, University of Northern Arizona, Flagstaff, said ' We have a kind of dialogue that we cannot interpret.'

Ann M. Hirsch of the University of California, Los Angeles, said, 'I still think it's the way of a dance, but maybe it's because I studied ballet for so long.' Ann and his colleague Angie Lee, now at the University of California, San Diego, describe this process in the ballet model in the work published by Plant Signaling & Behavior in 2006.

Soy beans (top left photo), a kind of African wild leaf clover (top right) and plants with the same family develop classic roots.African beach grass does not grow but also contains the nitrogen-fixing Burkholderia bacteria (bottom left).Gunnera (bottom right) also finds a cyanobacteria-like bacterium to fix nitrogen in the root bag.(Photo: USDA, Howieson, E. Cahill, iStockphoto)

They argue that this process begins with a pas de deux dance between the roots, the release of flavonoids into the soil, and the surrounding bacteria, which in turn release the so-called weak molecules. Factor Only a small amount of these substances can make calcium quickly move into the roots (according to Hirsch is Allergo). Usually in a few seconds, a burst of nodules is released, calcium also flows into the root fiber cells. A few more minutes, the calcium content starts to recede again and again, continuing for an hour. According to Hirsch, this could trigger the building-up genes.

If all goes well, the tiny roots twist into hooks and eventually twist around the bacteria. In many legumes, the root cells are swept open to an inner tunnel, or infective fiber, which leads the bacteria into their tissues - shelter - eventually bulging into nodules.

This ballet dance also contains many surprises. Last summer, two species of bacteria ORS278 and BTAi1 turned out to have no nodules. But bacteria can still form nodules in certain legume species in a respectable way.

Sharon Long, Stanford University expressed a positive attitude towards this finding.'This is quite important. Now the project has not answered anything but actually opened new questions. '

Plants can be quite careful when choosing for you to jump bacteria. For example, Howieson's current work finds that two species of clover select specific strains of Rhizobium leguminosarum even if they are rare in the surrounding soil environment. Howieson and colleagues wrote about this in Soil Biology and Biochemistry in March that a particularly effective bacterium will eventually be the ideal partner of clover even when their population is 100 times less Compared to other less effective partners, only nodules are formed but not fixed nitrogen. Other research groups are testing the genes that plants use in the process of negotiating with their partners. The SymRK gene encodes a protein involved in receiving nodal signals - a bacterial response to the plant's signaling partner.

However, according to Didier Bogusz of the Research and Development Institute in Montpellier, France, SymRK has other duties in legumes. Earlier works also showed that SymRK works in a long-standing relationship with legumes, similar to three-quarters of plants, allowing the formation of intimate relationships between roots and fungi. This rooted fungal network is called arbuscular mycorrhizae and brings nutrients like phosphates from the soil to the plant.

Free cyanobacteria, such as Mastigocladus laminosus, fixed a lot of nitrogen and proved to be important in global nutrient rings.(Photos: G. Wanner, Getty Images)

Australian casuarina trees with fluffy foliage are not of the legume family, and they are not associated with bean group bacteria. Currently, Bogusz discovered that, like legumes, the plant relies on SymRK when they group with other nitrogen fixing bacteria, Frankia. Bogusz and colleagues also presented in March 25, Proceedings of the National Academy of Sciences. This plant also uses SymRK to connect to a mushroom network version. This finding supports a theory that plants use nitrogen fixation nodules that have evolved energy by borrowing elements of extensive ancient systems to form a collaborative relationship with fungi.
The future of nitrogen fixed food crops

Bogusz argues that nitrogen-fixing genes are discovered and create the ability to fix nitrogen on non-bean crops 'highly probable for a long time '.

According to Eric Triplett, University of Florida in Gainesville, it is now possible to be a good time for a revival for the re-crop. Early efforts in the 1970s did not progress much, but due to the lack of ongoing support and tools available today. Last year he gave a speech to the National Research Council on the prospects of this success.

Triplett opposed the idea of ​​trying to remove the legume's ability to find suitable bacteria and develop nodules to another species basically like corn. To do that, it is necessary to adjust a whole set of specialized plant genes to find special bacterial partners. ' I have a feeling that things are not too difficult. For me, the only way to do this is to transform plants directly with nitrogen-fixing genes. '

Bacteria perform miracles with more than 20 genes, but plants only have some versions of them. He suggested putting this mechanism into one of the energy metabolizers that are already active in plant cells, such as mitochondrial energy or chloroplasts that capture light.'I don't think there's anything more important than you can do to deliver food to sub-Saharan Africa.'

Even if putting nitrogen-fixing genes directly into plants that promise an easier method, this is still difficult. For example, Downie noted that it would be costly and compromised if this complex mechanism could appear in a new plant. Despite its biochemical ability, plants will still need a large amount of energy to break down the three nitrogen bonds. Calculations based on microbial enzymes estimate that treating a molecule of N2 requires more ATP molecules, the energy unit of the cell, than processing the CO2 molecule in photosynthesis at least 8 times. This energy will not be used for other functions, such as creating leaves or beans.

Crops that make their own nitrogen often produce less yield than fertilized corn and wheat. So adding the nitrogen fixation power may cause some species to reduce agricultural performance. Downie said 'You won't get anything from nothing. Will you accept a trade off? '

The decrease in productivity may be a disadvantage but according to Vaclav Smil, University of Manana, Canada, there is another way of looking at the supply of nitrogen. He watched the use of nitrogen in the world and he did not expect genetic engineers to create a self-produced fertilizer in a short time.'They have promised it for a long time.'

'With diets like today, about 40% of all food is produced by artificial fertilizers'. But that dependency comes from a food system that he calls 'all wrongly managed'.

Smil gives data about excess and waste from a table. For example, fertilizer funds vary widely based on food choices, especially how much meat and milk a country consumes. The US diet, based on about 50% of man-made fertilizer, consumes almost 5 times meat per Asian diet.

The challenges of providing nitrogen for the world's current food habits are real, but he thinks it is wrong to wait for the introduction of nitrogen fixing wheat flour.'Reduce the loss of food. Before putting gene therapy into everything, change your diet. '

Part 1