Transcript Bio 226: Cell and Molecular Biology

Pathogens
• Agrobacterium tumefaciens
• Agrobacterium rhizogenes
• Pseudomonas syringeae
• Pseudomonas aeruginosa
• Viroids
• DNA viruses
• RNA viruses
• Fungi
• oomycetes
• nematodes
Symbionts
• N-fixers
• Endomycorrhizae
• Ectomycorrhizae
Mineral Nutrition
Macronutrients: CHOPKNSCaFeMg
• Ca: signaling, middle lamella, cofactor
• Fe: cofactor
• Mg: cofactor
• mobile in plant, so shows first in old leaves
Mineral Nutrition
Micronutrients: BNaCl others include Cu, Zn, Mn
• B: cell elongation. NA metabolism
• Na: PEP regeneration, K substitute
• Cl: water-splitting, osmotic balance
• Cu: cofactor
• immobile in plant, so shows first in young leaves
Mineral Nutrition
Soil nutrients
•Amounts & availability vary
•Many are immobile, eg P, Fe
Mineral Nutrition
Nutrients in soil
•Plants alter pH @ roots to aid uptake
• Also use symbionts
• Mycorrhizal fungi help: especially with P
Mineral Nutrition
Also use symbionts
•Mycorrhizal fungi help: especially with P
• P travels poorly: fungal hyphae are longer & thinner
• Fungi give plants nutrients
• Plants feed them sugar
• Ectomycorrhizae surround root: only trees, esp. conifers
Mineral Nutrition
Ectomycorrhizae surround root: trees
•release nutrients into apoplast to be taken up by roots
Endomycorrhizae invade root cells: Vesicular/Arbuscular
• Most angiosperms, especially in nutrient-poor soils
Rhizosphere
Endomycorrhizae invade root cells: Vesicular/Arbuscular
• Most angiosperms, especially in nutrient-poor soils
• May deliver nutrients into symplast
• Or may release them when arbuscule dies
Rhizosphere
Endomycorrhizae invade root cells: Vesicular/Arbuscular
• Most angiosperms, especially in nutrient-poor soils
• Deliver nutrients into symplast or release them
when arbuscule dies
Also find bacteria, actinomycetes, protozoa associated
with root surface = rhizosphere
Rhizosphere
Also find bacteria, actinomycetes, protozoa associated
with root surface = rhizosphere
• Plants feed them lots of C!
Rhizosphere
Also find bacteria, actinomycetes, protozoa associated
with root surface = rhizosphere
• Plants feed them lots of C!
• They help make nutrients available
Rhizosphere
Also find bacteria, actinomycetes, protozoa associated
with root surface = rhizosphere
• Plants feed them lots of C!
• They help make nutrients available
• N-fixing bacteria supply N to many plant spp
N assimilation by N fixers
Exclusively performed by prokaryotes
Dramatically improve the growth of many plants
N assimilation by N fixers
Exclusively done by prokaryotes
Most are free-living in soil or water
N assimilation by N fixers
Exclusively done by prokaryotes
Most are free-living in soil or water
Some form symbioses with plants
N assimilation by N fixers
Exclusively done by prokaryotes
Most are free-living in soil or water
Some form symbioses with plants
Legumes are best-known, but
many others including mosses,
ferns, lichens
N assimilation by N fixers
Exclusively done by prokaryotes
Most are free-living in soil or water
Some form symbioses with plants
Legumes are best-known, but
many others including mosses,
ferns, lichens
Also have associations where
N-fixers form films on leaves or
roots and are fed by plant
N assimilation by N fixers
Exclusively done by prokaryotes
Also have associations where
N-fixers form films on leaves or
roots and are fed by plant
All must form O2-free
environment for nitrogenase
N assimilation by N fixers
All must form O2-free
environment for nitrogenase
O2 binds & inactivates electron
-transfer sites
N assimilation by N fixers
O2 binds & inactivates electron
-transfer sites
Heterocysts lack PSII, have
other mechs to lower O2
N assimilation by N fixers
Heterocysts lack PSII, have
other mechs to lower O2
Nodules have special
structure + leghemoglobin
to protect from O2
Nodule formation
Nodules have special structure + leghemoglobin to protect
from O2
Bacteria induce the plant to form nodules
Nodule formation
Bacteria induce the plant to form nodules
1. Root hairs secrete chemicals that attract N-fixers
Nodule formation
Bacteria induce the plant to form nodules
1. Root hairs secrete chemicals that attract N-fixers
2. Bacteria secrete Nod factors that induce root hair to
coil up. Nod factors determine species-specificity
Nodule formation
1. Root hairs secrete chemicals that attract N-fixers
2. Bacteria secrete Nod factors that induce root hair to
coil up. Nod factors determine species-specificity
3. Nod factors induce degradation of root cell wall
Nodule formation
3. Nod factors induce degradation of root cell wall
4. Plant forms "infection thread"=internal protusion of
plasma membrane that grows into cell
5. When reaches end of cell bacteria are released into
apoplast and repeat the process on inner cells
Nodule formation
5. When reaches end of cell bacteria are released into
apoplast and repeat the process on inner cells
6. Cortical cells near xylem form a nodule primordium
Nodule formation
5. When reaches end of cell bacteria are released into
apoplast and repeat the process on inner cells
6. Cortical cells near xylem form a nodule primordium
7. When bacteria reach these cells the infection thread
breaks off, forming vesicles with bacteria inside
Nodule formation
7. When bacteria reach these cells the infection thread
breaks off, forming vesicles with bacteria inside
8. Vesicles fuse, form the peribacteroid membrane and
bacteria differentiate into bacteroids.
Nodule formation
8. Vesicles fuse, form the peribacteroid membrane and
bacteria differentiate into bacteroids.
9. Plant cells differentiate into nodules
Nodule formation
8. Vesicles fuse, form the peribacteroid membrane and
bacteria differentiate into bacteroids.
9. Plant cells differentiate into nodules: have layer of cells
to exclude O2 & vasculature
to exchange nutrients
Nodule formation
Plant cells differentiate into nodules: have layer of cells to
exclude O2 & vasculature to exchange nutrients
Complex process that is difficult to engineer: 21 nonlegume plant genera have N-fixers
Nitrogen fixation
N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi
Catalysed by nitrogenase, a very complex enzyme!
Nitrogen fixation
N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi
Catalysed by nitrogenase, a very complex enzyme!
Also catalyzes many other reactions
Usually assayed by acetylene reduction
Nitrogen fixation
N2 + 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi
Usually assayed by acetylene reduction
Sequentially adds 2 H per cycle until reach NH3
Nitrogen fixation
Sequentially adds 2 H per cycle until
reach NH3
May then be exported to cytosol &
assimilated by GS/GOGAT or assimilated
inside bacteroid
Nitrogen fixation
Sequentially adds 2 H per cycle until
reach NH3
May then be exported to cytosol &
assimilated by GS/GOGAT or assimilated
inside bacteroid
Are then converted to amides or ureides
& exported to rest of plant in the xylem!
Nutrient uptake
Most nutrients are dissolved in water
Nutrient uptake
Most nutrients are dissolved in water
• Enter root through apoplast until hit endodermis
Nutrient uptake
Most nutrients are dissolved in water
• Enter root through apoplast until hit endodermis
• Then must cross plasma membrane
Crossing membranes
A) Diffusion through bilayer
B) Difusion through protein pore
Selective
C) Facilitated diffusion
D) Active transport
E) Bulk transport
Active
1) Exocytosis
2) Endocytosis
Nutrient uptake
Then must cross plasma membrane
• Gases, small uncharged & non-polar molecules diffuse
Nutrient uptake
Then must cross plasma membrane
• Gases, small uncharged & non-polar molecules diffuse
down their ∆ [ ]
• Important for CO2, auxin & NH3 transport
Nutrient uptake
Then must cross plasma membrane
• Gases, small uncharged & non-polar molecules diffuse
down their ∆ [ ]
• Polar chems must go through proteins!
Selective Transport
1) Channels
integral membrane proteins with pore that specific ions
diffuse through
Selective Transport
1) Channels
integral membrane proteins with pore that specific ions
diffuse through
• depends on size
& charge
Channels
integral membrane proteins with pore
that specific ions diffuse through
• depends on size & charge
• O in selectivity filter bind
ion (replace H2O)
Channels
integral membrane proteins with pore
that specific ions diffuse through
• depends on size & charge
• O in selectivity filter bind
ion (replace H2O)
• only right one fits
Channels
O in selectivity filter bind
ion (replace H2O)
• only right one fits
• driving force?
electrochemical D