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 PotatoNewLeaf Potato Papaya Ring Spot Virus Resistant Papaya Improving nutrition Golden rice Potato: reducing acrylamide Improving shelf-life FlavrSavr tomato. FlavrSavr Making vaccines, other useful biochems

Photosynthesis in the real world The 3 most important factors limiting photosynthesis 1.Light 2.pCO 2 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 CO 2 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

Plants and Temperature PSII sets T opt & upper limit for C4 plants T opt for C3 also depends on photorespiration -> varies with pCO 2

Plants and Temperature PSII sets T opt & upper limit for C4 plants T opt for C3 also depends on photorespiration -> varies with pCO 2 Have respiration compensation point

Plants and Temperature PSII sets T opt & upper limit for C4 plants T opt 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 pCO 2 rubisco usually limits C3 -> limited by demand for CO 2 Supply is limited by resistance to CO 2 diffusion Boundary layer Stomatal: only one that can be adjusted Liquid phase

Photosynthesis in the real world pCO 2 rubisco usually limits C3 -> limited by demand for CO 2 Supply is limited by resistance to CO 2 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 pCO 2 Demand is set by mesophyll, stomata control supply C i is usually much lower than C a A vs C i plots tattle on the Calvin cycle

Photosynthesis in the real world pCO 2 A vs C i 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 pCO 2 Currently Rubisco usually limits C3 plants, but pCO 2 is going up

Photosynthesis in the real world pCO 2 Currently Rubisco usually limits C3 plants, but pCO 2 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 pCO 2 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 pCO 2 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!