Nitrogen and Sulfur Assimilation

Flashcards on Nitrogen and Sulfur Assimilation in Plants

Nitrogen

The most abundant mineral element in a plant, often the limiting nutrient for plant growth, and found in amino acids, nucleic acids, and chlorophyll.

Biological Nitrogen Fixation

Conversion of atmospheric N2 into ammonium, representing the key entry point of molecular nitrogen into the biogeochemical cycle.

Free-living bacteria

Aerobic, facultative, or anaerobic organisms capable of fixing nitrogen; examples include Azotobacter, Gloeothece, Rhodospirillum, and Clostridium.

Anabaena

Nitrogen-fixing cyanobacterium with thick-walled heterocysts providing an anaerobic inner environment for nitrogen fixation under aerobic conditions.

Nodulin (Nod) genes

Genes in plants specific to nodules.

Nodulation (nod) genes

Rhizobial genes participating in nodule formation, including common nod genes (nodA, nodB, nodC) and host-specific nod genes (nodP, nodQ, nodH).

Nod factors

Lipochitin oligosaccharide signal molecules that have a chitin backbone and a fatty acyl chain which elicits a response from a particular host plant species.

Biological Nitrogen Fixation Reaction

The overall reaction is N2 + 8 e– + 8 H+ + 16 ATP →2 NH3 + H2 + 16 ADP + 16 Pi

Fe protein

Component of the nitrogenase enzyme complex; smaller one with two identical subunits containing an iron–sulfur cluster.

MoFe protein

Component of the nitrogenase enzyme complex; has four subunits and contains two Mo–Fe–S clusters.

Leghemoglobin

An oxygen-binding heme protein found in root nodules that helps to maintain a low oxygen level to protect nitrogenase.

Hydrogenase

Enzyme that can split the H2 formed by nitrogenase, generating electrons for N2 reduction and improving the efficiency of nitrogen fixation.

Amides and ureides

Transported forms of nitrogen in plants, with amides exported by temperate-region legumes and ureides exported by legumes of tropical origin.

Nitrate reductase

Enzyme that catalyzes the first step of nitrate assimilation: reduction of nitrate to nitrite in the cytosol.

Nitrite reductase

Enzyme that catalyzes the second step of nitrate assimilation: reduction of nitrite to ammonia in the plastids.

Glutamine synthetase (GS)

Enzyme that combines ammonium with glutamate to form glutamine; cytosolic forms are involved in nitrogen transport, while plastid forms re-assimilate photorespiratory NH4 +.

Glutamate synthase (GOGAT)

Enzyme that transfers the amino group of glutamine to 2-oxoglutarate, yielding two molecules of glutamate.

Glutamate dehydrogenase (GDH)

An enzyme that catalyzes a reversible reaction that synthesizes or deaminates glutamate.

Rapidly converted

Organic forms in the root nodules before being transported to the shoot via the xylem

Plants

An important part of the global sulfur cycle

Sulfate

The absorbed form of sulfur in plants

Cysteine

The first step in the synthesis of sulfur-containing organic compounds is the reduction of sulfate to the amino acid

APS kinase

Catalyzes a reaction of APS with ATP to form 3-phosphoadenosine-5-phosphosulfate (PAPS).

Sulfotransferases

Transfer the sulfate group from PAPS to various compounds, including choline, brassinosteroids, flavonol, gallic acid glucoside, glucosinolates, peptides, and polysaccharides.

Glutathione

Amino acid derivative involved in Redox reactions Oxidation /reduction, metal transport and detox