mineral nutrition in plants ii oh oh, i get by with a little help from my friends. - ringo starr et...
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Mineral Nutrition in Plants II
OhOh, I get by with a little help from my friends.
- Ringo Starr et al.
Today
• Nitrogen Assimilation;
• Mychorhizzae;
• Questions.
Structural Elements, Covalently Bonded IGroup 1: Nutrients that are parts of carbon compounds...
• N: amino acids, proteins, nucleic acids, co-enzymes, etc.
– forms three covalent bonds,– chains, rings, branches,– one pair unshared electrons for metal coordination,– carbon “substitute”; distorts symmetry in rings and chains,– participates in hydrogen bonding,– metal complexion (see chlorophyll),
• Triple bond is extremely stable.
History
Varro praeceptis adicit equino sit levissium segetes alendi, prata vero graviore quod ex hordeo fiaat multasque gignat herbas…inter omnes autem constat nihil esse utilis lupini segete priusquam siliquetur aratro vel bidentibus versa manipuisve desectae circa radices arborum ac vitium obrutis…
- Pliny the Elder (~A.D. 80)
Haber-Bosch Reaction
N
NN2 gas
…as a reactant, is of limited use to most living organisms,
…some prokaryotes can break the triple bond and form ammonia,
…eukaryotes do not have the enzymes required to perform this task.
Nitrogen Gas
…plants assimilate nitrate and ammonium,
– NO3- and NH4
+ .
Oxidation State
Name
Nitrogen Species
Sources: Industrial 80 tg
Lightning 19 tgBiotic 170 tg
Lost: Volatilization 100 tg
Denitrification 210 tgLeaching 36 tg
Plant Assimilation1200 tg
Symbiotic
+
Terrestrial System
Free-Living Nitrogen Fixation
• Cyanobacteria (blue green algae),
– i.e. Anabaena,
Anabaena
- heterocysts: cells adapted for nitrogen fixation;
• no O2.
• Other bacteria,
Anaerobic: maintain anaerobic lifestyles,Facultative: can switch to anaerobic metabolism,Aerobic: adapt specific cells for “anaerobic” metabolism.
Nitrogen Fixation is Sensitive to O2
N2 8 protons
Ammonia and H2
Output.
O2 is a good electron acceptor.
8 reduced ferredoxins
Sources of Fixed Nitrogen I
Fig. 37.9
Oxidation of ammonium yields energy for carbon
fixation.
Decomposition of complex organic
molecules.
Nitrogen Assimilation I
• NO3- can be assimilated in either the root or
shoot,
– NO3- is absorbed by the root, stored in the vacuole,
assimilated, or transported to leaves,
– NO3- is reduced to nitrite,
– NO2- is reduced to form ammonium,
• uses light reactions of photosynthesis for reducing power in leaves,
• ferrodoxin reduction by plastid metabolism in roots,
• NH4+ (from the soil matrix, or from NO3
- reduction) is incorporated into amino acids for use, or for N transport.
Nitrate Toxicity• NO3
- is not generally toxic to plants and can be readily stored and transported,
• It is toxic, in high concentrations, to other organisms,
– Methemoglobinemia (“blue baby syndrome”),
• liver reduces nitrate to nitrite (or at higher pH, via bacteria in the gut),• nitrite oxidizes iron in hemoglobin, (Fe2+ ---> Fe3+),• renders hemoglobin unable to bind O2,
– Nitrosamines,
• R2NNO or RNHNO,• Extremely mutagenic and carcinogenic.
Nitrogen Fixation Requires Energy
16 ATPs for hydrolysis
8 reduced ferredoxins
N2 8 protons
Ammonia and H2
Output.
…why would bacteria associate with plants
Plant N2 Symbionts Nitrogen Assimilation II
• Plants supply reducing power,
• Bacteria provide fixed nitrogen,
– Alder (trees), Ceanothus (shrub),
• Frankia (bacteria),
– Sugarcane,
• Nostoc (bacteria),
– Azolla/Fairy Fern (water fern),
• Anaebena, (cyanobacteria)
Azolla Anabaena
Ceanothus cordulatus; Mountain Whitethorn
Azolla/Anabaena
Azolla Anabaena
Arrows point to
Anabaena strands.
Azolla cross section
• Anabaena grows in leaf axes and lacuna.
Azolla/Anabaena/Rice/Humans
3. Stomp (or machine smash),
4. Fixed nitrogen is released to soil.
1. Spread Azolla, let grow,
2. Break clumps, drain paddy,
More History
shu (soybean)
Chou scholars (~1000 B.C.)
Soy Root Nodules: result from an infection by Rhizobium.
Nitrogen FixationRhizobium symbionts
Rhizobium Infection I
1. Emerging root hair sends chemical attractants (elicitors),
2. Bacteria respond with a recognition signal,
if compatible?
3. Root hair grows and curls around the bacterial colony,
4. Bacteria proliferate within the curl.
Sweet Talk?
1. Plant secretes a specific elicitor
(flavonoid).
2. Bacterial receptor recognizes signal, and transports it across cell
membrane,
3. Flavanoid binds transcription factor (Nod D), complex
bids DNA,
4. nod genes are expressed,
5. Nod factor is produced (a molecule with host specificity),
6. Nod factor is recognized by the host, in turn activating host genes for proper response.
Rhizobium Infection II
5. Plant cell wall is degraded,
6. Plant plasma membrane invaginates root hair cell,
7. Infection thread reaches root hair plasma membrane, fuses,
8. Bacteria enter the apoplast.
Rhizobium Infection III
9. New infection threads form,
10. Threads form toward “target cells”,
11. Bacteria “bleb” off of the infection thread, into the cytosol,
12. Bacteria are surrounded by a plant membrane.
Nodule Formation12. Bacteria are surrounded by a plant membrane.
- bacterial induce plant cell division in infected and surrounding cells,
- cells in the pericycle begin dividing, (similar to lateral root formation).
13. Affected pericycle and cortical derived cells continue to divide until the regions fuse.
14. Vasculature forms between the nodule and the plant stele,
- nitrogenous compounds are carried to the plant,
- nutrients to the bacteria.
Nitrogen Assimilation II
• Symbiosome,
– plant membrane, surrounding…
– one or more bacteria,
• once inside a symbiosome, bacteria differentiate into bacteroids,
• bacteroids may differentiate,
• Host Cell Synthesizes,
– transport proteins for the symbiosome membrane,
– leghemoglobin, an oxygen binding molecule,
– N assimilation enzymes.
Symbiosomes
Figure 37.10
Nitrogen Assimilation I vs. II
• Cost of symbiosis (to the plant),
– unless there is a nitrogen deficit, plants without rhizobium infection generally do better than infected plants,
– generally,
• high NO32-, no R (best growth),
• high NO32-, R (good growth),
• low NO32-, R (good growth),
• low NO32-, no R (poor growth).
I II
Mycorrhizae Phosphate Extraction
…phosphate (HPO42-) is readily absorbed by
roots via a H+ / HPO42- symporter,
…however, HPO42- has low solubility and high
sorption capacity in soil,
– low concentration in the soil (1M or less), millimolar in root cells,
... Mycorrhizae increase the root surface area, actively transport HPO4
2-. Eucalyptus Root/Hartig Net
Absorbtion of Water and Minerals by Roots
Mycorrhizae
ectotropic mycorrhizal fungi
• penetrate the intercellular spaces of the root cortex,
• surround the root to form a dense fungal sheath.
vesicular-arbuscular fungi
• penetrate the intercellular spaces of the root cortex, and penetrate cortical cells,
– do not break the plant plasma membrane,– hyphae/plant structures form that exchange
nutrients.
Focus? Chapter 37?
• Excretion?• Essential Elements?
– Groups 1 - 4,
• Phytochelation and Phytoremediation?• Dose Response curves and Nutrient Deficiencies?• Nitrogen and Nitrogen Assimilation,
– Nitrate and Ammonium Assimilation,– Nitrogen Symbionts,
• Mychorrhizae?