Next Assignment = GMO plantsIn 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

Lipid metabolismUnique aspects in plantsMake fatty acids by same reactions, but in plastids with a prokaryoticfatty acid synthase12 proteins, cf one multifunctional protein

Lipid metabolismMake 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 metabolismSource of acetyl-CoA is controversial• Most comes from plastid PDH• Some comes from cytoplasmic acetate; activated in cp• Also used to makesterols, some aminoacids, many others

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!

Lipid metabolismUnique aspects in plantsChloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol

Lipid metabolismUnique aspects in plantsChloroplasts have lots of galactolipids: sugar linked directly to diacylglycerol: saves PO4

Lipid metabolismUnique aspects in plantsChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cp-> most abundant lipid on earth!

Lipid metabolismUnique aspects in plantsChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cpB) DGDG (Digalactosyl diacylglycerol) 28% cp

Lipid metabolismChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cpB) DGDG (Digalactosyl diacylglycerol) 28% cpC) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp

Lipid metabolismChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cpB) DGDG (Digalactosyl diacylglycerol) 28% cpC) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp• Very unsaturated!

Lipid metabolismChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cpB) DGDG (Digalactosyl diacylglycerol) 28% cpC) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp• Very unsaturated!• Makes membranes very fluid

Lipid metabolismChloroplasts have lots of galactolipids: sugar linked directly to

diacylglycerol : saves PO4

A) MGDG (Monogalactosyl diacylglycerol) 50% cpB) DGDG (Digalactosyl diacylglycerol) 28% cpC) SQDG ( Sulphoquinovosyldiacylglycerol) 16% cp• Very unsaturated!• Makes membranes very fluid• Source of 3 FA

Lipid metabolismUnique aspects in plants1) Make fatty acids in plastids2) large amounts of galactolipids3) Oleosomes: oil-storing organelles with only outer leaflet

Lipid metabolismOleosomes: oil-storing organelles with only outer leaflet • Put oils between the leaflets as they are made

Lipid metabolismOleosomes: 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 metabolismOleosomes: 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 metabolismUse fats to store carbon as well as energy!!??• Recover C via glyoxylate cycle & gluconeogenesis

Lipid metabolismBiological roles• Plasma membrane lipids helpsurvive freezing

Lipid metabolismBiological roles• Plasma membrane lipids helpsurvive freezing• Unacclimated cells vesiculate as they lose water & pop when it returns

Lipid metabolismBiological roles• Plasma membrane lipids helpsurvive freezing• Unacclimated cells vesiculate as they lose water & pop when it returns• Acclimated cells shrivel & reswell

Lipid metabolismBiological 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 metabolismBiological roles• Plasma membrane lipids help survive freezing• Mito lipid composition may also influence chilling sensitivity• CS plants (eg bananas) are damaged at 10˚ C• Mito show defects at <10˚ C not seen in other plants

Lipid metabolismCS plants (eg bananas) are damaged at 10˚ C• Mito show defects at <10˚ C not seen in other plants• Membrane lipids show phase changes at these T

Lipid metabolismCS plants (eg bananas) are damaged at 10˚ C• Mito show defects at <10˚ C not seen in other plants• Membrane lipids show phase changes at these T• Blamed on saturated PG

Lipid metabolismBiological (& commercial) roles• Plasma membrane lipids help survive freezing• Mito lipid composition influences chilling sensitivity• Mito show defects at <10˚ C not seen in other plants• unsaturated FA did not fix CS, but saturated FA made it

worse: reason for GM desaturases

Lipid metabolismOther commercial aspects• Yield and quality of seed oil is very important:12 million

tons/year

Lipid metabolismOther 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

Lipid metabolismOther 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 metabolismOther commercial aspects• Yield and quality of seed oil is very important:12 million tons/yr• Also have markets for many specialized oils

Lipid metabolismOther 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