Skotomorphogenesis Seed germination Genes and enzymes Embryo and Seed development Photomorphogenesis Photoreceptors Phytochrome Cells and cell growth Phytochrome: regulation of light responses Photosynthesis: light reaction Photosynthesis: carbon fixation Photorespiration Respiration Plant nutrition Nitrogen fixation

Current US population (300 mio.) 2050 population (520 mio.) Arable land1.7 acres 0.6 acres Fresh water1,300 gal. 700 gal. energy2,500 gal. oil 1,600 gal. oil Food exports$155 $0 food mixmeat 31%/69% plant meat 15%/85% plant food cost100% 300 – 500%

Arable land in the USA

What do you see?

Nitrogen in plants

Nitrogen fertilizer use

Nitrogen in plants Seeds Leaves Roots Plant tissue Protein contains N stored in fruit and seeds N is important part of growth regulators N is part of plant structure N is part of proteins and enzymes in roots Chlorophyll contains N

Nitrogen in plants the N-cycle N2 in air Biological fixation through bacteria: 170 mio. t/year Uptake through plants from soil: 1200 mio. t/year Loss as ammonium into atmosphere: 100 mio t/year Loss as bound onto soil particles: 10 mio. t/year Loss through bacterial denitrification: 210 mio. t/year Loos by leaching into groundwater: 36 mio. t/year 8% 2% 90%

Nitrogen in plants Nitrogen is highly abundant in plant cells just like O, C, H Proteins, nucleotides (DNA, RNA), sec. metabolites N 2 fixation into NH 3 or NO 3 - (Haber-Bosch) HB-process: 200ºC, 200 at (80 mio.t/y) Natural N2-fixation: (190 mio.t/y) lightning (8%) N 2 -> HNO 3 photochemical processes (2%) NO + O 3 -> HNO 3 biolog. N2 fixation (90%) N 2 -> NH4

Nitrate assimilation Nitrate (NO 3 - ) + NADPH + H + +2e - NO H 2 O + NADP + (uptake in roots) Nitrite (NO 2 - ) + 8H + + 6Fd red + 6e - NH Fd ox + 2H 2 O (toxic) Nitrate Reductase Nitrite Reductase Chloroplasts Cytoplasm NH 4 + into amino acids (amino group)

Nitrate assimilation Nitrate (NO 3 - ) + NADPH + H + +2e - NO H 2 O + NADP + (uptake in roots) Nitrate Reductase Cytoplasm Flavin Adenine DinucleotideMolybdenum complex reduces nitrate 2e - (from respiration) 2e -

Nitrate assimilation Nitrite (NO 2 - ) + 8H + + 6Fd red + 6e - NH Fd ox + 2H 2 O (toxic) Nitrite Reductase Chloroplasts Photosynthesis ETC Iron-sulfur

Ammonium assimilation Ammonium (NH 4 + )+Glutamate+ATP Glutamine+ADP+P i Mg 2+, Mn 2+, Co 2+ Cofactor Isoenzymes in Cytoplasm, chloroplasts Glutamine synthetase (GS) Glutamate synthase (GOGAT) Glutamine + 2-oxoglutarate + NADH 2 Glutamate+NAD + Chloroplasts

Ammonium assimilation Glutamate synthase (GOGAT) Glutamine + 2-oxoglutarate + NADH 2 Glutamate+NAD + Chloroplasts

Ammonium assimilation Ammonium (NH 4 + )+Glutamate+ATP Glutamine+ADP+P i Mg 2+, Mn 2+, Co 2+ Cofactor Isoenzymes in Cytoplasm, chloroplasts Glutamine synthetase (GS) Glutamate dehydrogenase (GDH) NH oxoglutarate + NADPH Glutamate+NADP + + H 2 O chloroplasts, mitochondria Alternative pathway of ammonium assimilation

Ammonium assimilation Ammonium (NH 4 + )+Glutamate+ATP Glutamine+ADP+P i Mg 2+, Mn 2+, Co 2+ Cofactor Isoenzymes in Cytoplasm, chloroplasts Glutamine synthetase (GS)

Ammonium assimilation Glutamate+oxalacetate Aspartate+2-oxoglutarate Aspartate aminotransferase (Asp-AT) Glutamine+ Aspartate+ ATP Asparagine +Glutamate+ ADP +Pi Asparagine synthetase (AS) Cytoplasm, chloroplasts, mitochondria, peroxisomes, glyoxysomes Cytoplasm

Ammonium assimilation Glutamine+ Aspartate+ ATP -> Asparagine +Glutamate+ ADP +Pi Asparagine synthetase (AS)

Ammonium assimilation Glutamate+oxalacetate Aspartate+2-oxoglutarate Aspartate aminotransferase (Asp-AT) Vitamin B 6 cofactor

Amino acid biosynthesis

Nitrogen assimilation in plants N O3- Nitrate N O2- Nitrite N H4+ Ammonium N H2-CH H COOH Amino Acids Uptake from the soil Nitrate reductase Nitrite reductase GS/GOGAT Protein biosynthesis

Nitrogen assimilation in plants ASNiRNR AS: asparagine synthetase NiR: nitrite reductase NR: nitrate reductase Uptake from the soil NHS NHS: nitrate-proton-symporter NO 3 -

Nitrogen fixation Plants live in symbiosis with N 2 -fixing bacteria The nitrogenase enzyme complex allows to fix N2 from air N2 + 16ATP +8 H + +8e - -> 2NH H ADP + 16P i Nitrogenase enzyme complex This is a tough job, requiring a lot of energy (16ATP!) and specialist equipment

Nitrogen fixation Plants live in symbiosis with N 2 -fixing bacteria The nitrogenase enzyme complex allows to fix N2 from air N2 + 16ATP +8 H + +8e - 2NH H ADP + 16P i SU1 SU2 Nitrogenase enzyme complex

Nitrogen fixation Plants live in symbiosis with N 2 -fixing bacteria The nitrogenase enzyme complex allows to fix N2 from air N2 + 16ATP +8 H + +8e - 2NH H ADP + 16P i SU1SU2 Nitrogenase enzyme complex e-e- e-e- e-e- e-e- N2 fixation NO reduction Azide reduction Acetylene reduction H2 production ATP hydrolysis

Nitrogen fixation N 2 -fixing bacteria live in association with plants incl. rhizobium They live inside root nodules formed by leguminous plants N2 + 16ATP +8 H + +8e - -> 2NH H ADP + 16P i Root nodules of soybean infected with R. japonicum Veg. cell Het.cyst N 2 -fixing cyanobacterium Anabaena

Nitrogen fixation How do we get these nodules? A.) Rhizobia bind to root hairs (iso-flavonids, betaine) B.) Rhizobia bind to root hairs (nodulins, nod factors) Root hair curling

Nitrogen fixation C.) Rooty hair cell wall degraded, infection thread, Golgi secretory vesicles D.) Fusion of infection thread and plasma membrane of root hair cell

Nitrogen fixation E.) Rhizobia released into apoplast, infect second root hair cell F.) Infection thread branches, release of bacteria enclosed by plant plasma membrane, peribacterial m. G.) Bacteroids (N 2 -fixing) form nodules

Nitrogen fixation Fixation of NH3 into either amides (asparagine or glutamine) (pea, broad bean, lentil) or ureides (allantoic acid, allantoin, citrulline) (soybean, kidney bean, peanut) Plant ureides