Part 3 Plant Mineral Nutrition 3. 1 Overview of nitrogen in the biosphere and in plants
Part 3 Plant Mineral Nutrition 3.1 Overview of nitrogen in the biosphere and in plants
The nitrogen cycle Organic N Nitrogen fixation NH OH NO NO. NO
The nitrogen cycle
Nitrogen deficiency phenotype in leaves of sugar beet Nitrogen deficiency is often associated with uniform yellowing of older leaves
Nitrogen deficiency phenotype in leaves of sugar beet. Nitrogen deficiency is often associated with uniform yellowing of older leaves
Overview of N uptake by a nonnodulated plant (left) and by a nodulated plant with N-fixing symbionts(right) NO2→NH4+Amno Amino acid No2NH4→-Amin Amides ureides Vacuole Plastid NO2→NH4+-Amin Plastid acias NO A GIn NO3 Vacuole Root NO NHa Nodulated root
Overview of N uptake by a nonnodulated plant (left), and by a nodulated plant with N-fixing symbionts (right)
Table 3.1 Rates of natural and anthropogenic nitrogen fixation Se ource Amount of n fixed Lighting 10 Tg/year e Biological N-fixation in terrestrial systems 90-140 Tg/year o Biological N-fixation in marine systems 30-300 Tg/year e Nfertilizer synthesis 80 Tgye ear e Fossil fuel combustion 20 Tg/year g=1012
Table 3.1 Rates of natural and anthropogenic nitrogen fixation ⚫ Source Amount of N fixed ⚫ Lighting 20 Tg/year ⚫ * Tg =1012 g
3.2 Biological nitrogen fixation o 3.2. 1 Nitrogen fixation reduces nitrogen gas to ammonia, at the cost of ATP and reducing equivalent o N+16 atP+8e+8H-2NH+H+16 ADP +16 Pi o Eukaryotes cannot utilize dinitrogen, but some prokaryotes are able to catalyze the enzymatic reduction of this compound to ammonia o 3.2.2 Nitrogen fixation is sensitive to oxygen
3.2 Biological nitrogen fixation ⚫ 3.2.1 Nitrogen fixation reduces nitrogen gas to ammonia, at the cost of ATP and reducing equivalent. ⚫ N2 + 16 ATP + 8 e - + 8 H→ 2 NH3 + H2 + 16 ADP + 16 Pi ⚫ Eukaryotes cannot utilize dinitrogen, but some prokaryotes are able to catalyze the enzymatic reduction of this compound to ammonia. ⚫ 3.2.2 Nitrogen fixation is sensitive to oxygen
3.2.3 Enzymology of nitrogen fixation (A) (B) Nitrogenase complex Fe protein MoFe protein (NifH) (NifD, NifK FeMoco) Dinitrogenase Dinitrogenase Fe protein reductase MoFe 8 Fdx Sox 2 NH3+ H2 8 Faxed N2+8H Fe MoFered MoF Protein 16 ( ADP
3.2.3 Enzymology of nitrogen fixation
Table 3.2 Substrates and products of nitrogenase Substrate Product NH3 H+ H ●N,O N. HO NH3, CH4 CHCH
Table 3.2 Substrates and products of nitrogenase ⚫ Substrate Product ⚫ N2 NH3 ⚫ H+ H2 ⚫ N2O N2 , H2O ⚫ CN- NH3 , CH4 ⚫ C2H2 C2H4 , C2H6
3.3 Symbiotic nitrogen fixation
3.3 Symbiotic nitrogen fixation
3.3.1 Some vascular plants establish nitrogen-fixing symbioses o There are three major types of nitrogen-fixing symbioses o 1)Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants(Fabaceae) and at least one non legume, Parasponia(ulmaceae) o 2)Gram-positive actinomycete genus( Frankia)and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle( Myrica), Casuarina and Ceanothus o 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots(e.g, Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern, associates symbiotically with the cyanobacterium
3.3.1 Some vascular plants establish nitrogen-fixing symbioses ⚫ There are three major types of nitrogen-fixing symbioses. ⚫ 1) Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants (Fabaceae) and at least one non legume, Parasponia(Ulmaceae). ⚫ 2) Gram-positive actinomycete genus ( Frankia) and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle(Myrica), Casuarina, and Ceanothus. ⚫ 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots (e.g.,Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern , associates symbiotically with the cyanobacterium
