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 ba

cteria 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 [CO2],

photoassimilation proceed

[CO2]

inhibit photoassimilation

inhibit photorespiration

C/N assimilation

C4 plants: photoassimilation occur in mesophyll cells, [CO2] low

High [CO2] in bundle sheath cells

Inhibit photoassimilation

Assimilatory quotient(AQ) CO2 assimilated / O2 evolved

as a function of light level

Wheat seedling

Photoassimilation

no photoassimilation

(no photoinhibition)

Photoassimilation:

CO2 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

CO2 itself and ATP regeneration

(2) stroma

(3)

WebEssay 12.1

The plants receiving NH4+ were

more responsive to CO2 enrichment than those receiving NO3

-

Doubling CO2 (enrichment):

short-term:

accelerate carbon fixation in C3 plants by about 30%

long-term (days to weeks):

carbon fixation declines until it stabilizes at a rate that averages

12% above ambient controls

CO2 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+– SO42- 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 + O2 + BH2 AO + H2O + 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