Transcript Mineral Nutrition in Plants II

Mineral Nutrition in Plants II
Oh
Oh, I get by with a little help from my friends.
- Ringo Starr et al.
Today
• Nitrogen Assimilation;
• Mychorhizzae;
• Questions.
Structural Elements, Covalently Bonded I
Group 1: Nutrients that are parts of carbon compounds...
• N: amino acids, proteins, nucleic acids, coenzymes, 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
Nitrogen Gas
N
N
N2 gas
Nitrogen Species
Oxidation
State
Name
…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.
…plants assimilate nitrate and
ammonium,
– NO3- and NH4+ .
Terrestrial System
+
Symbiotic
Sources:
Industrial 80 tg
Lightning 19 tg
Biotic
170 tg
Lost:
Volatilization 100 tg
Denitrification 210 tg
Leaching
36 tg
Plant Assimilation
1200 tg
Free-Living Nitrogen Fixation
• Cyanobacteria (blue green algae),
– i.e. Anabaena,
• Other bacteria,
Anabaena
- heterocysts:
cells adapted for
nitrogen fixation;
Anaerobic: maintain anaerobic lifestyles,
Facultative: can switch to anaerobic metabolism,
Aerobic: adapt specific cells for “anaerobic” metabolism.
• no O2.
Nitrogen Fixation is Sensitive to O2
Ammonia
and H2
Output.
8 reduced
ferredoxins
N2
O2 is a good electron acceptor.
8 protons
Sources of Fixed Nitrogen I
Oxidation of ammonium
yields energy for carbon
fixation.
Decomposition of
complex organic
molecules.
Fig. 37.9
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 NO3reduction) 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
Ammonia
and H2
Output.
8 reduced
ferredoxins
N2
8 protons
16 ATPs for hydrolysis
…why would bacteria associate with plants
Plant N2 Symbionts
Nitrogen Assimilation II
• Plants supply reducing power,
• Bacteria provide fixed nitrogen,
– Alder (trees), Ceanothus (shrub),
Ceanothus cordulatus; Mountain Whitethorn
• Frankia (bacteria),
– Sugarcane,
• Nostoc (bacteria),
– Azolla/Fairy Fern (water fern),
• Anaebena, (cyanobacteria)
Azolla
Anabaena
Azolla/Anabaena
• Anabaena grows
in leaf axes and
lacuna.
Azolla
Anabaena
Arrows
point to
Anabaena
strands.
Azolla cross section
Azolla/Anabaena/Rice/Humans
1. Spread Azolla, let grow,
2. Break clumps, drain paddy,
3. Stomp (or machine smash),
4. Fixed nitrogen is released to soil.
More History
shu (soybean)
Chou scholars (~1000 B.C.)
Soy Root Nodules: result from an
infection by Rhizobium.
Nitrogen Fixation
Rhizobium symbionts
Rhizobium Infection I
if compatible?
1. Emerging root hair sends chemical
attractants (elicitors),
3. Root hair grows and curls around the
bacterial colony,
2. Bacteria respond with a recognition
signal,
4. Bacteria proliferate within the curl.
Sweet Talk?
3. Flavanoid binds
transcription factor
(Nod D), complex
bids DNA,
2. Bacterial receptor
recognizes signal,
and transports it
across cell
membrane,
1. Plant secretes a
specific elicitor
(flavonoid).
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,
11. Bacteria “bleb” off of the infection
thread, into the cytosol,
10. Threads form toward “target cells”,
12. Bacteria are surrounded by a plant
membrane.
Nodule Formation
12. 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+ / HPO42symporter,
…however, HPO42- has low solubility
and high sorption capacity in soil,
– low concentration in the soil (1mM or
less), millimolar in root cells,
... Mycorrhizae increase the root
surface area, actively transport
HPO42-.
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?