The infection process during nodule organogenesis ─ occur simultaneously Plant: attractants Rhizobia: Nod factors Cell wall degradation Infection thread formation Fuse with the membrane of root cell Penetrate and new infection thread formation Branching and extending bacteria released into the cytosol Bacteroids: a nitrogen-fixing endosymbiotic organelles (p. 301R)

The energetic of nutrient assimilation ¤ nitrate  ammonium consumes ca. 25% of the total energy less than 2% of the total dry weight produce ¤ occur in the stroma of the chloroplast ¤ Photoassimilation: coupling nutrient assimilation to photosynthetic e - transport use the surplus reductants of Calvin cycle  high light, low [CO 2 ], photoassimilation proceed  [CO 2 ]  inhibit photoassimilation inhibit photorespiration C/N assimilation

C 4 plants: photoassimilation occur in mesophyll cells, [CO 2 ] low High [CO 2 ] in bundle sheath cells  Inhibit photoassimilation

Assimilatory quotient(AQ)  CO 2 assimilated / O 2 evolved as a function of light level Wheat seedling Photoassimilation  no photoassimilation (no photoinhibition)

Photoassimilation: CO 2 fixation may interfere with nitrate photoassimilation (1) (1) NADH is supported by chloroplast via malate shuttle (2) The level of reduced ferredoxin (3) The acidification of stroma dissipate the pH gradient CO 2 itself and ATP regeneration (2) stroma (3)

WebEssay 12.1 The plants receiving NH 4 + were more responsive to CO 2 enrichment than those receiving NO 3 -

Doubling CO 2 (enrichment): short-term: accelerate carbon fixation in C 3 plants by about 30% long-term (days to weeks): carbon fixation declines until it stabilizes at a rate that averages 12% above ambient controls CO 2 acclimation shoot N and proteins contents diminish WebEssay 12.1

Sulfur assimilation § Sources: The weathering of parent rock material Industrial contamination, the burning of fossil fuels releases sulfur dioxide and hydrogen sulfide § Absportion pathways: sulfate: H + – SO 4 2- symporter of the roots from the soil sulfur dioxide take up from stomata ＞ 0.3 ppm, 8 h  extensive tissue damage § Location mostly in leaves which can supply reduced ferredoxin and serine (p. 305R) § The transported form in the phloem glutathione (Gly-Cys-  -Glu), also acts as a signal that coordinates the absorption of sulfate by the roots and the assimilation of sulfate by the shoot

Activated form 2 In plastids In cytosol gallic acid glucoside, glucosinolates, polysaccharides (photorespiration)

Cysteine  Methionine (Web topic 12.3) S-adenosylmethionine

Sulfur assimilation § Functions: The structural and regulatory roles in proteins, disulfide bridges Electron transfer through iron-sulfur clusters Catalytic sites for several enzymes and coenzymes Secondary metabolites such as Nod factors, antiseptic alliin in garlic, and anticarcinogen sulforaphane in broccoli

Oxygen assimilation ¤ Respiration (major) Photorespiration: rubisco oxygenase activity (major) oxygen fixation (minor): oxygen assimilated into organic compounds ¤ the types of oxygenases dioxygenase: monooxygenase: mixed-function oxidase

cell wall protein extensin, posttranslation A + O 2 + BH 2  AO + H 2 O + B hydroxylation demethylation In ER

Cation assimilation ¤ K, Mg, Ca, Cu, Fe, Mn, Co, Na, Zn ¤ coordination bonds and electrostatic bonds p. 306L neutralization oxalate