Transcript Bio 226: Cell and Molecular Biology

Next Assignment = GMO plants
In class starting March 27
Herbicide resistance
• Bromoxynil
• Glyphosate (roundup)
• Glufosinate (Basta)
• Isoxaflutole (Balance, Corvus, Prequel)
• Dicamba/2,4-D
•Pathogen/herbivore resistance
• BT (Bacillus thuringiensis toxin)
• Colorado Potato Beetle (CPB) Resistant NewLeaf Potato
• Papaya Ring Spot Virus Resistant Papaya
•Improving nutrition
• Golden rice
• Potato: reducing acrylamide
•Improving shelf-life
• FlavrSavr tomato.
•Making vaccines, other useful biochems
Photosynthesis in the real world
The 3 most important factors limiting photosynthesis
1. Light
2. pCO2
3. Temp
Remember that
water limits yield,
but indirectly on
PS.
Photosynthesis in the real world
Light
• Absorb it very well
• Rarely have the best amount!
Photosynthesis in the real world
Light
• Sun leaves often have too much
• Shade leaves often have too little PAR
Photosynthesis in the real world
Light
• Sun leaves often have too much
• Shade leaves often have too little PAR
• Sun leaves: thicker, more PSII, protein & xanthophyll
• light compensation pt:
more cells = more mito
Photosynthesis in the real world
Light
• Sun leaves: thicker, more PSII, protein & xanthophyll
• light compensation pt: more cells = more mito
• Shade leaves: thinner, more PSI & chl, > chlb/chla
Photosynthesis in the real world
Light
• Cells at top of leaf absorb most light
• Cells at bottom get most CO2
• Cells in middle do most photosynthesis!
Plants and Temperature
Affects enzymes
Affects membranes
• Fluidity: must be correct
• Too stiff, may leak if too cold
Plants and Temperature
Affects enzymes
Affects membranes
• Fluidity: must be correct
• Too stiff, may leak if too cold
• Denature if too warm
Plants and Temperature
Affects enzymes
Affects membranes
• Fluidity: must be correct
• Too stiff, may leak if too cold
• Denature if too warm
• PSII denatures first!
• Lipids & proteins denature
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Plants and Temperature
PSII sets Topt & upper limit for C4 plants
Topt for C3 also depends on photorespiration -> varies with pCO2
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Plants and Temperature
PSII sets Topt & upper limit for C4 plants
Topt for C3 also depends on photorespiration -> varies with pCO2
Have respiration compensation point
Plants and Temperature
• PSII sets Topt & upper limit for C4 plants
• Topt for C3 also depends on photorespiration
• Limiting factor varies at lower T depending on which enzymes fall
behind -> rubisco usually limits C3
Photosynthesis in the real world
Heat dissipation
• Long wave-length radiation
• Sensible heat loss
• Conduction &
convection to cool air
• Evaporation
Photosynthesis in the real world
pCO2
• rubisco usually limits C3 -> limited by demand for CO2
• Supply is limited by resistance to CO2 diffusion
• Boundary layer
• Stomatal: only one
that can be adjusted
• Liquid phase
Photosynthesis in the real world
pCO2
• rubisco usually limits C3 -> limited by demand for CO2
• Supply is limited by resistance to CO2 diffusion
• Boundary layer
• Stomatal: only one
that can be adjusted
• Liquid phase
Demand is set by mesophyll,
Stomata control supply
Photosynthesis in the real world
pCO2
Demand is set by mesophyll, stomata control supply
Ci is usually much lower than Ca
A vs Ci plots tattle on the Calvin cycle
Photosynthesis in the real world
pCO2
A vs Ci plots tattle on the Calvin cycle
• In linear phase rubisco is limiting
• When curves RuBP or Pi regeneration is limiting
Photosynthesis in the real world
pCO2
• Currently Rubisco usually limits C3 plants, but pCO2 is going up
Photosynthesis in the real world
pCO2
• Currently Rubisco usually limits C3 plants, but pCO2 is going up
• Will increase plant growth until hit new limiting factor
Photosynthesis in the real world
• Will increase plant growth until hit new limiting factor
• Free-Air CO2 Enrichment Experiments show initial gains, but
taper off w/in a few years
Photosynthesis in the real world
• Will increase plant growth until hit new limiting factor
• Free-Air CO2 Enrichment Experiments show initial gains, but
taper off w/in a few years
• Now are limited by nutrients or water
Photosynthesis in the real world
pCO2
• Greenhouse effect on T will reduce production in many areas but
raise it in others
• Climate change will alter rainfall
Photosynthesis in the real world
pCO2
• Greenhouse effect on T will reduce production in many areas but
raise it in others
• Climate change will alter rainfall
• Overall prediction is
that crops will suffer in
many parts of world
Lipid metabolism
Most are glycerolipids: fatty acids bonded to glycerol
GLYCEROLIPIDS
Triacylglycerols = FAs on all 3 C
• store energy
GLYCEROLIPIDS
Bond FA to glycerol
Diacylglycerols = FAs on 2 Cs, headgroup on C 3
GLYCEROLIPIDS
Diacylglycerols = FAs on 2 Cs, headgroup on C 3
Form bilayers in water
Lipid metabolism
Unique aspects in plants
Make fatty acids by
same reactions, but in
plastids with a prokaryotic
fatty acid synthase
12 proteins, cf one
multifunctional
protein
Lipid metabolism
Make fatty acids in plastids with a prokaryotic FAS
• 12 proteins, instead of one multifunctional protein
• Assemble some lipids in CP, others in ER
Lipid metabolism
Make fatty acids in plastids with a prokaryotic FAS
• 12 proteins, instead of one multifunctional protein
• Assemble some lipids in CP, others in ER
• Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except
in grasses (profoxydim & other grass herbicides inhibit ACCase)
Lipid metabolism
• Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except
in grasses (profoxydim & other grass herbicides inhibit ACCase)
• Same biochem, but diff
location and enzymes
Lipid metabolism
• Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except
in grasses (profoxydim & other grass herbicides inhibit ACCase)
• Same biochem, but diff
location and enzymes
• In light cp make lots of
NADPH, and leaves are
main sinks for FA
Lipid metabolism
• Acetyl-CoA carboxylase is also prokaryotic = 4 subunits, except
in grasses (profoxydim & other herbicides inhibit ACCase)
• Same biochem, but diff
location and enzymes
• In light cp make lots of
NADPH, and leaves are
main sinks for FA
• But, each cell makes
its own FA, so NADPH
in other cells comes from
Pentose-Pi shunt
Lipid metabolism
Source of acetyl-CoA is controversial
• Most comes from plastid PDH
Lipid metabolism
Source of acetyl-CoA is controversial
• Most comes from plastid PDH
• Some comes from cytoplasmic acetate; activated in cp
• Also used to make
sterols, some amino
acids, many others
Lipid metabolism
Source of acetyl-CoA is controversial
• Most comes from plastid PDH
• Some comes from cytoplasmic acetate; activated in cp
• Also used to make sterols, some
amino acids, many others
• Why ACCase is “committed step”
Lipid metabolism
Assemble some lipids in CP, others in ER
• “16:3 plants” assemble lipids in cp using FA-ACP = prokaryotic
pathway (“primitive”)
Lipid metabolism
“16:3 plants” assemble lipids in cp using FA-ACP = prokaryotic
pathway (“primitive”)
“18:3 plants” export FA, assemble lipids in ER using FA-CoA =
eukaryotic pathway (“advanced”)
Lipid metabolism
“16:3 plants” assemble lipids in cp using FA-ACP = prokaryotic
pathway (“primitive”)
“18:3 plants” export FA, assemble lipids in ER using FA-CoA =
eukaryotic pathway (“advanced”)
Substrates for most desaturases
are lipids, not FA!