Bio%20226:%20Cell%20and%20Molecular%20Biology

1

• 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

2

• Photosynthesis in the real world
• The 3 most important factors limiting
  photosynthesis
• Light
• pCO2
• Temp
• Remember that
• water limits yield,
• but indirectly on
• PS.

3

• Photosynthesis in the real world
• Light
• Absorb it very well
• Rarely have the best amount!

4

• Photosynthesis in the real world
• Light
• Sun leaves often have too much
• Shade leaves often have too little PAR

5

• 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

6

• 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, gt chlb/chla

7

• 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!

8

• Plants and Temperature
• Affects enzymes
• Affects membranes
• Fluidity must be correct
• Too stiff, may leak if too cold

9

• Plants and Temperature
• Affects enzymes
• Affects membranes
• Fluidity must be correct
• Too stiff, may leak if too cold
• Denature if too warm

10

• 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

11

• Plants and Temperature
• PSII sets Topt upper limit for C4 plants
• Topt for C3 also depends on photorespiration -gt
  varies with pCO2

12

• Plants and Temperature
• PSII sets Topt upper limit for C4 plants
• Topt for C3 also depends on photorespiration -gt
  varies with pCO2
• Have respiration compensation point

13

• 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 -gt rubisco usually
  limits C3

14

• Photosynthesis in the real world
• Heat dissipation
• Long wave-length radiation
• Sensible heat loss
• Conduction
• convection to cool air
• Evaporation

15

• Photosynthesis in the real world
• pCO2
• rubisco usually limits C3 -gt limited by demand
  for CO2
• Supply is limited by resistance to CO2 diffusion
• Boundary layer
• Stomatal only one
• that can be adjusted
• Liquid phase

16

• Photosynthesis in the real world
• pCO2
• rubisco usually limits C3 -gt 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

17

• 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

18

• 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

19

• Photosynthesis in the real world
• pCO2
• Currently Rubisco usually limits C3 plants, but
  pCO2 is going up

20

• 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

21

• 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

22

• 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

23

• 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

24

• 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

25
Lipid metabolism Most are glycerolipids fatty
acids bonded to glycerol
26

• GLYCEROLIPIDS
• Triacylglycerols FAs on all 3 C
• store energy

27
GLYCEROLIPIDS Bond FA to glycerol Diacylglycerols
FAs on 2 Cs, headgroup on C 3
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GLYCEROLIPIDS Diacylglycerols FAs on 2 Cs,
headgroup on C 3 Form bilayers in water
29

• 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

30

• 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

31

• 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)

32

• 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

33

• 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

34

• 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

35

• Lipid metabolism
• Source of acetyl-CoA is controversial
• Most comes from plastid PDH

36

• 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

37

• 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

38

• Lipid metabolism
• Assemble some lipids in CP, others in ER
• 163 plants assemble lipids in cp using FA-ACP
  prokaryotic pathway (primitive)

39

• Lipid metabolism
• 163 plants assemble lipids in cp using FA-ACP
  prokaryotic pathway (primitive)
• 183 plants export FA, assemble lipids in ER
  using FA-CoA eukaryotic pathway (advanced)

40

• Lipid metabolism
• 163 plants assemble lipids in cp using FA-ACP
  prokaryotic pathway (primitive)
• 183 plants export FA, assemble lipids in ER
  using FA-CoA eukaryotic pathway (advanced)
• Substrates for most desaturases
• are lipids, not FA!