a Mineral food. Nitrogen fixing

you are: a Mineral food

One of the major problems of the biochemists interested in increase of efficiency of agriculture, efficiency increase azotfiksatsii as growth of plants limits insufficient supply by their fixed nitrogen more often is. Nitrogen in the form of stable molecule N2 makes 80% of atmosphere. Before fixing (restoration of nitrogen to ammonia) this molecule should be destabilised and split somehow. Ammonia formed at fixing (NH3) can be absorbed by roots of plants as that or after its oxidation by soil microorganisms to nitrates (N03-). In the majority of soils formation NO3 - from NH3 occurs so quickly that the nitrogen most part is absorbed by roots in a kind NO3-.

Nitrogen Fixing is carried out mainly by some freely living bacteria consuming organic substance of soil. Them concern, for example, aerobic form Azotobacter and anaerobnaja - Clostridium. Bacteria of sort Rhizobium which too participate in nitrogen fixing, live in root tumours or klubenkah certain kinds of plants (fig. 7.3). The Plant-owner belongs usually to family bean, including peas, beans, a soya, a lucerne, a clover and viku. Recently conducted researches have shown that azotfiksirujushchie bacteria of sort Spirillum surround roots of tropical grass Digitaria. This weak association of roots of a grass and bacteria in rizosfere, probably, represents an intermediate evolutionary stage between svobodnozhivushchim azotobakterom and localised in klubenkah rizobiumom. The plant ' involves ' bacteria by means of organic root vydeleny. Microorganisms rizosfery in turn supply plants with the fixed nitrogen. Some blue-green seaweed (such as and Nostoc) and photosynthesizing bacteria (Rhodospirillum) can fix Apaaepa atmospheric nitrogen, energetically interfacing this process to photosynthesis. The specified organisms are the most expressed avtotrofa biological worlds though some shtammy Apaaepa live and effectively fix nitrogen only in association with special ' pockets ' water fern Azolla. The reasons of this phenomenon are not found out.

The Mutually advantageous association of two organisms is called as symbiosis. As Rhizobium, a plant-owner separately are not capable to fix and restore atmospheric nitrogen, a biological complex in klubenke it is necessary to consider as symbiotic association of bacteria and a plant-owner. Each type of a plant-owner has own symbiotic Rhizobium. The mutual cognizance of a plant-owner and bacteria is carried out by an attachment of special fiber (lektina), being on a surface of cages of a root hair, to a specific bacterium. After an attachment to the owner the interfering organism gets into cages of unusually bent root hairs which, obviously, are deformed under the influence of allocated with bacteria rostovyh group hormones auksina. In a bacterium cage-owner share, and the formed posterity changes the form, turning in bakteroidy, containing in an infectious thread which passes from a top of a cellular wall of a root hair through the cage centre (fig. 7.4).

Definitive result of such penetration of bacteria is extremely strong growth of cages of the root, leading to formation of the warty cambers named klubenkami. Rizobium it is capable to fix effectively nitrogen, only being in klubenkah of this kind.

The Association between Spirillum and its plant-owner too concerns to symbiotic, but it is limited by a surface of roots. It is less strong type of association as Spirillum it is possible to grow up separately from the owner in the presence of enough of nutrients. Therefore scientists study possibility large-scale kultivirovanija these bacteria as sources of the fixed nitrogen. Also it has been shown that sometimes the given bacteria live in association with corn. It opens deducing possibility shtammov, capable to nitrogen fixing on those kinds of plants which usually have azotfiksirujushchih no bacteria.

Nitrogen Fixing is carried out Fe2 + - and Mo_-soderzhashchim by enzyme nitrogenazoj. The plants living in association with azotfiksirujushchimi by bacteria and depending on this enzyme, do not react to addition azotsoderzhashchih fertilizers as ammonia (NH3), present at them or formed of brought azotsoderzhashchego a material, suppresses activity of the genes operating synthesis nitrogenazy. Therefore attempts to raise level azotfiksatsii include searches azotfiksirujushchih the bacteria deprived of ability to regulate synthesis nitrogenazy by a principle ' of a feedback '. In the adjustable mechanism, obviously, enzyme glutaminsintetaza as synthesis nitrogenazy occurs only at the high maintenance glutaminsintetazy is involved. Recently the mutant bacteria containing a considerable quantity glutaminsintetazy have been found. They continue to synthesise njtrogyonazu even in the presence of NH3. Thus, search of bacteria with high efficiency azotfiksatsii seems promising.

Except nitrogenazy which contacts molecule N2 and destabilises it, for restoration N2 to NH3 are necessary a strong reducer and ATR. Ferredoksin - the carrier elektronov, participating as well in photosynthesis, - serves as the main reducing agent. At symbiotic azotfiksatsii ATR it is delivered by a plant the owner and the quantity of the fixed nitrogen is often limited to speed of photosynthesis. Therefore ' fertilising ' a plant, for example a soya, carbon dioxide, basically it is possible to raise the general fixing of nitrogen thanks to quantity increase metabolitov, formed at photosynthesis. However it is difficult for carrying out in practice at cultivation of field cultures.

azotfiksirujushchie systems it is possible to poison All even sledovymi with quantities of oxygen. It means that enzyme nitrogenaza even in aerobic cages should contain basically in anaerobnyh conditions. In root klubenkah bean it is reached with the help leggemoglobina (LHb) - reddish ferriferous analogue of an animal pigment. Like haemoglobin of blood and mioglobinu muscles, leggemoglobin can contact oxygen:

Such linkage provides effective removal of the oxygen which is nearby from nitrogenazy, and optimum speeds azotfiksatsii. The oxygen connected with leggemoglobinom, can be used also for formation ATR in the course of breath. It has very much great value as significant amounts ATR are necessary for nitrogen fixing. As a rule, the is more red klubenek, the more actively in it there are processes azotfiksatsii. In - azotfiksirujushchej blue-green seaweed Nostoc nitrogenaza, obviously, it is localised in geterotsistah, special not photosynthesizing anaerobnyh cages (fig. 7.5). This structural organisation serves also for isolation azotfiksirujushchej systems from the oxygen allocated in the course of photosynthesis.

Some microorganisms living in soil, can oxidise ammonia (NH3) to nitrates (NO3-). The majority of plants prefer to absorb, and to use the nitrogen brought in the form of nitrate though such nitrogen as a result joins in a vegetative material in the form of highly-restored amino groups (-NH2). Enzyme nitratreduktaza restores nitrates back to ammonium by means of the restored respiratory carriers, such, as NADPH. Nitratreduktaza, possibly, contains molybdenum in the active centre, and it, probably, is the main metabolic role of molybdenum in plants. Restoration N03 ~ to NH3 can, obviously to occur through such intermediate connections, as nitrogenous acid (HONO) and gidroksilamin (NH2OH).

Ammonia is toxic for vegetative cages, therefore it should not collect in them in considerable quantities. Ammonia usually turns to amino acids, entering reaction with a-ketoglutarovoj acid (metabolit a cycle of Krebsa) therefore acid is formed glutaminovaja, and at the further addition of ammonia - glutamin, amidglutaminovoj acids (fig. 7.6).

Other amino acids are synthesised in a course fermentativnogo reamination process at which glutaminovaja acid co-operates with others ketokislotami, predecessors of new amino acids, transferring on them the amino group and turning again in a-ketoglutarovuju acid. Asparaginovaja acid is one of the first products of reaction of reamination. In this case as an amino group receptor acid serves shchavelevouksusnaja. At additional linkage of ammonia with asparaginovoj acid it is formed asparagin - amid asparaginovoj acids. Mainly in the form of these four components - glutaminovoj acids, glutamina, asparaginovoj acids and asparagina - the fixed nitrogen from cages also is transported poring on all plant. Some amino acids are formed by updating of a carbon skeleton of preexisting amino acid.

Thus, the general circulation of nitrogen in the nature represents reversible transition of its free gaseous form in atmosphere in the fixed form in soil or biological system. In vegetative cages the absorbed nitrates are restored again to ammonia which then contacts certain organic acids therefore amino acids, and then fibers are formed. These substances are digested animals and turn to animal protein and nitrogenous products of an exchange - urea and uric acid. Finally all animals and plants die off and decay in soil with formation of simple nitrogenous substances, such, as ammonia. These substances constantly retsirkulirujut through biological systems, creating nitrogen circulation (fig. 7.7).

Thanks to action denitrifitsirujushchih bacteria the fixed nitrogen in the form of free molecular nitrogen comes back in atmosphere, whence it again can be fixed by bacteria. Denitrifikatsija - prodigal enough process. It can be slowed down now in soil by means of the chemical compounds specially intended for this purpose. Their application should render the essential help to agriculture.

Enzyme nitrogenaza which contacts a molecule. N2 (N=N) also restores it to ammonia (NH3), can attach also acetylene (NANOSECOND=SN) and to restore it to etilena (NANOSECOND=SN). Detection of this activity underlies a method with which help azotfiksirujushchuju activity of a plant can be defined directly in the field. The certain quantity of acetylene in the form of gas is brought in a root the manned environment of a plant and after a while leaves ' the Quantity of acetylene transformed in etilen, serves as an indicator azotfiksirujushchej to ability of roots of the given plant. As as acetylene, and etilen are gases, even their insignificant quantities can be analyzed the method of a gas chromatography allowing without the big expenses quickly to obtain the exact data. Using this method, physiologists of plants investigated azotfiksirujushchuju ability of plants of a soya in ontogeneze and have studied the physiological factors influencing efficiency of process. It is important for revealing of ways of the further increase of efficiency of plants.