Nitrogen assimilation
Encyclopedia
Nitrogen assimilation is a fundamental biological process that occurs in plant
s and algae
that are incapable of independent nitrogen fixation
. The assimilation of nitrogen
has marked effects on plant productivity, biomass, and crop yield, and nitrogen deficiency leads to a decrease in structural components. Initial conversion of nitrate
to nitrite
(by nitrate reductase) is followed by a reduction to ammonia
by nitrite reductase
(also called nitrite oxidoreductase). The ammonia is incorporated into glutamine
as an amido nitrogen and is reductively transferred to 2-oxoglutarate to form 2 molecule
s of glutamate by glutamate synthase. The general steps of assimilation have been known for several years, however, the chemical mechanisms that occur in these processes remain poorly understood in large part due to the lack of detailed structural information concerning the enzyme
s that catalyze these reactions.
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s and algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
that are incapable of independent nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
. The assimilation of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
has marked effects on plant productivity, biomass, and crop yield, and nitrogen deficiency leads to a decrease in structural components. Initial conversion of nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
to nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
(by nitrate reductase) is followed by a reduction to ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
by nitrite reductase
Nitrite reductase
Nitrite reductase refers to any of several classes of enzymes that catalyze the reduction of nitrite. There are two classes of NIR's. A multi haem enzyme reduces NO2 to a variety of products. Copper containing enzymes carry out a single electron transfer to produce nitric oxide.- Iron based...
(also called nitrite oxidoreductase). The ammonia is incorporated into glutamine
Glutamine
Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders...
as an amido nitrogen and is reductively transferred to 2-oxoglutarate to form 2 molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s of glutamate by glutamate synthase. The general steps of assimilation have been known for several years, however, the chemical mechanisms that occur in these processes remain poorly understood in large part due to the lack of detailed structural information concerning the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s that catalyze these reactions.