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 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 “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!

Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyl diacylglycerol) 16% cp

Lipid metabolism Chloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol : saves PO4 A) MGDG (Monogalactosyl diacylglycerol) 50% cp B) DGDG (Digalactosyl diacylglycerol) 28% cp C) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp Very unsaturated! Makes membranes very fluid Source of 3 FA

Lipid metabolism Oleosomes: oil-storing organelles with only outer leaflet Put oils between the leaflets as they are made Add oleosin proteins to outside: curve the membrane

Lipid metabolism Oleosomes: oil-storing organelles with only outer leaflet Put oils between the leaflets as they are made Add oleosin proteins to outside: curve the membrane Oils often have unusual fatty acids

Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Unacclimated cells vesiculate as they lose water & pop when it returns Acclimated cells shrivel & reswell

Lipid metabolism Biological roles Plasma membrane lipids help survive freezing Mito lipid composition may also influence chilling sensitivity CS plants (eg bananas) are damaged at 10˚ C

Lipid metabolism Other commercial aspects Yield and quality (especially unsaturation) of seed oil is very important:12 million tons/year Want more double bonds, especially w-3, for health Want less double bonds for shelf life and taste Each double bond increases p(oxidation) 40x Have GM oils with more & less double bonds

Lipid metabolism Other commercial aspects Yield and quality of seed oil is very important Also have markets for many specialized oils Have genetically-engineered many crops to alter seed oils or produce specific fats

Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils to make them volatile

Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils to make them volatile Projected to be 10% of european diesel in 2018

Lipid metabolism Biofuels are now very fashionable Biodiesel = fatty acid methyl esters Trans-esterify oils, used cooking oil, etc Projected to be 10% of european diesel in 2018 Also use coconut & other oils directly in diesel engines

Lipid metabolism Also use coconut & other oils directly in diesel engines Just need to be sufficiently fluid to reach cylinder

Lipid metabolism Also use coconut & other oils directly in diesel engines Just need to be sufficiently fluid to reach cylinder Add double bonds to fatty acids or make them shorter

Lipid metabolism Also use coconut & other oils directly in diesel engines Just need to be sufficiently fluid to reach cylinder Add double bonds to fatty acids or make them shorter Problem: shifting from growing food to growing fuel!

Biofuels

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum Only use part of plant

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum Only use part of plant Can yield 1.3x more energy than needed to grow, harvest & convert it to ethanol

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum Only use part of plant Can yield 1.3x more energy than needed to grow, harvest & convert it to ethanol Usually lose C

Biofuels Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum Only use part of plant Can yield 1.3x more energy than needed to grow, harvest & convert it to ethanol Usually lose C Use crops for fuel instead of food

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Inefficient Only use part of plant Use crops for fuel instead of food 2nd gen (cellulosic) Ethanol Use cell walls as source of sugar for yeast

Biofuels 2nd gen (cellulosic) Ethanol Use cell walls as source of sugar for yeast Can use entire plant

Biofuels 1st gen Ethanol Yeast makes EtOH from plant sugar Corn, sugar cane, sugar beet, sorghum Only use part of plant Use crops for fuel instead of food 2nd gen (cellulosic) Ethanol Use cell walls as source of sugar for yeast

Biofuels 2nd gen (cellulosic) Ethanol Use cell walls as source of sugar for yeast Can use entire plant Can use non-crops grown on marginal land Switchgrass (Panicum virgatum) C4 perennial: grows from Mexico to 55˚ N

Biofuels Switchgrass (Panicum virgatum) Can yield 5.4 x more energy than needed to grow, harvest & convert it to ethanol cf 1.3 x max for corn Also used for soil conservation and phytoremediation

Biofuels Miscanthus giganteus Sterile hybrid of M. sinensis X M. sacchariflorus (both from Asia)

Biofuels Miscanthus giganteus Sterile hybrid of M. sinensis & M. sacchariflorus (both from Asia) C4 perennial that reproduces solely through rhizomes

Biofuels Miscanthus giganteus Sterile hybrid of M. sinensis & M. sacchariflorus (both from Asia) C4 perennial that reproduces solely through rhizomes Non-invasive cf both parents, even though grows > 4m tall cf 1-2 m max for both parents

Biofuels Miscanthus giganteus Non-invasive cf both parents, even though grows > 4m tall cf 1-2 m max for both parents High N efficiency + C4 = grows well on barren land

Biofuels Miscanthus giganteus Non-invasive cf both parents, even though grows > 4m tall cf 1-2 m max for both parents High N efficiency + C4 = grows well on barren land Can yield 20 tons biomass/acre cf 7.6 for corn & 6 for switchgrass

Biofuels Miscanthus giganteus Can yield 20 tons biomass/acre cf 7.6 for corn & 6 for switchgrass could supply 12% of the EU's energy by 2050 Trees Poplar

Biofuels Trees Poplar Eucalyptus Can be harvested in 4-5 years Low maintenance Yield <4 tons biomass/acre cf 20 for M. giganteus

Biofuels 2nd gen (cellulosic) Ethanol Use cell walls as source of sugar for yeast Can use entire plant Can use non-crops grown on marginal land Problem: lignin & other wall chems

Biofuels Mutate plants to make simpler cell walls 10% of Arabidopsis genes are estimated to be involved in plant cell wall metabolism Many mutants reduce lignin synthesis Easier to digest cell walls Easier for pathogens to attack More prone to xylem collapse

Biofuels Biodiesel = fatty acid methyl esters Trans-esterify oils to make them volatile Renewable Fuels Standard (RFS2): US must use > 1 billion gallons/year in 2012 through 2022 (cf ~40 billion/year total) > 50% reduction in CO2 cf petrodiesel 2.1 billion gallons of biodiesel were used in 2015 Diamond Green Diesel in LA makes 275 million gallons/year

Biofuels Oils from plants and algae

Biofuels Algal oil production