Plant Respiration Releases 50% of fixed CO 2 Provides energy for all sinks,

Plant RespirationReleases 50% of fixed CO2

Provides energy for all sinks,source leaves at night & helps source during day!

Plant RespirationSimilar, but more complex than in animalsMaking precursors, recycling products, releasing energy are also important

Plant Respiration1. Glycolysis in cytosol2. Pyruvate oxidation in mito3. Krebs cycle in mito4. Electron transport &chemiosmosis in mito

Plant Respiration1. Glycolysis in cytosol• 1 glucose -> 2 pyruvate• Yields 2 NADH & 2 ATPper glucoseUnique features in plants1. May start with DHAPfrom cp instead of glucose

Unique features in plants1.May start with DHAP from cp instead of glucose2.May yield malate cf pyr• PEP ->OAA by PEPC, then reduced to malate

Plant Respiration2.May yield malate cf pyr• PEP ->OAA by PEPC, then reduced to malate• Get more ATP/NADH in mito

Unique features in plants2.May yield malate cf pyr• PEP ->OAA by PEPC, then reduced to malate• Get more ATP/NADH in mito• Replaces substrates

Plant Respiration1.Glycolysis in cytosol• 1 glucose -> 2 pyruvate• Yields 2 NADH & 2 ATPper glucoseAnaerobic plants ferment pyr to regenerate NAD+Form EtOH

Plant Respiration1.Glycolysis in cytosol• 1 glucose -> 2 pyruvate• Yields 2 NADH & 2 ATPper glucoseAnaerobic plants ferment pyr to regenerate NAD+Form EtOHLess toxic than lactate because diffuses away

Plant Respiration3. Krebs cycle• Similar, but more complexKey role is making intermediates & recycling products

Plant Respiration3. Krebs cycle• Similar, but more complexKey role is making intermediates & recycling productsMany ways to feed in other substrates to burn

Plant Respiration3. Krebs cycle• Similar, but more complexKey role is making intermediates & recycling productsMany ways to feed in other substrates to burn or replace intermediates used for biosynthesis

Plant RespirationMany ways to feed in other substrates to burn or replaceintermediates usedfor biosynthesisNeeded to keepcycle going

Plant RespirationMany ways to feed in other substrates to burn or replaceintermediates usedfor biosynthesisNeeded to keepcycle going

Plant RespirationMany ways to feed in other substrates to burn or replaceintermediates usedfor biosynthesisNeeded to keepcycle goingMalic enzyme is key:lets cell burn malate or citrate from othersources

Plant RespirationMany ways to feed in other substrates to burn or replace intermediates usedfor biosynthesisNeeded to keep cycle goingMalic enzyme is key: lets cell burnmalate or citrate from other sourcesPEPCarboxylase lets cell replace Krebs intermediates used for synthesis

Plant RespirationPentose phosphate shunt in cytosol or cp• 6 glucose-6P + 12NADP++ 7 H2O -> 5 glucose-6P + 6 CO2

+ 12 NADPH +12 H+ : makes NADPH & intermediates

Plant RespirationPentose phosphate shunt in cytosol or cpmakes NADPH & intermediatesUses many Calvin Cycle enzymes

Plant RespirationPentose phosphate shunt in cytosol or cpmakes NADPH & intermediatesUses many Calvin Cycle enzymesMakes nucleotide & phenolic precursors

Plant RespirationUses many Calvin Cycle enzymesMakes nucleotide & phenolic precursorsGets Calvin cycle started at dawn

ATP generation2 stages1) e- transport2) chemiosmotic ATP synthesis

Three steps transport H+ across membrane

1) NADH dehydrogenase pumps 4 H+/ 2 e-

2) Cyt bc1 pumps 4 H+/ 2 e-

3) Cyt c oxidase pumps 2 H+/ 2 e- and adds 2 H+ to O to form H2O

e- transportPlants have additional enzymes!•NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+

Additional e- transport enzymes!•NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone

Additional e- transport enzymes!•NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone•Helps burn off excess NADH from making precursors

Additional e- transport enzymes!•NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone•Helps burn off excess NADH from making precursors•Much lower affinity for NADH than complex I

Additional e- transport enzymes!•NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone•Helps burn off excess NADH from making precursors•Energy is released as heat

•NADH dehydrogenase in intermembrane space that transfers e- from NADH to UQ w/o pumping H+

Additional e- transport enzymes!•NADH dehydrogenase in intermembrane space that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone• "imports" e- from cytoplasmic NADH •Much lower affinity for NADH than complex I•Energy is released as heat

Additional e- transport enzymes!•NADPH dehydrogenase in intermembrane space that transfers e- from NADPH to UQ w/o pumping H+ Insensitive to rotenone• "imports" e- from cytoplasmic NADPH

Additional e- transport enzymes!•Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ •Insensitive to Cyanide, Azide or CO•Sensitive to SHAM (salicylhydroxamic acid)

Additional e- transport enzymes!•Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ •Insensitive to Cyanide, Azide or CO•Sensitive to SHAM (salicylhydroxamic acid,)•Also found in fungi, trypanosomes & Plasmodium

Additional e- transport enzymes!•Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ •Also found in fungi, trypanosomes & Plasmodium•Energy lost as heat: can raise Voodoo lilies25˚ C

Additional e- transport enzymes!•Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ • Plants also have an uncoupler protein: lets H+ in w/o doing work!

Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency?

Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency?

Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency?• Regenerate NAD+ needed for precursor synthesis• Generate heat• Burn off excess energy captured by photosynthesis• Prevalence says they're doing something important!

Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency?• Regenerate NAD+ needed for precursor synthesis• Generate heat• Burn off excess energy captured by photosynthesis• Prevalence says they're doing something important!

Regulating RespirationRegulated by demand for ATP, NADPH and substrates

Glycolysis is allosterically regulated at 3 irreversible stepsHexokinase is allosterically inhibited by its product: G-6PAllosteric site has lower affinity than active site

Glycolysis is allosterically regulated at 3 irreversible stepsHexokinase is allosterically inhibited by its product: G-6PPyr kinase is allosterically inhibited by ATP & citrate

Regulating GlycolysisMain regulatory step is PhosphofructokinaseRate-limiting step

Committed step

Regulating GlycolysisMain regulatory step is Phosphofructokinase

Inhibited by Citrate, PEP & ATP Stimulated by

ADP

Regulating Pyruvate DHMainly by a kinase•Inhibited when Pi added

Regulating Pyruvate DHMainly by a kinase•Inhibited when Pi added•NADH, Acetyl CoA, ATPNH4+ inhibit PDH & activate kinase

Regulating Pyruvate DHMainly by a kinase•Inhibited when Pi added•NADH, Acetyl CoA, ATPNH4+ inhibit PDH & activate kinase•Activated when no Pi•ADP, pyruvate inhibitkinase

REGULATING THE KREBS CYCLE Krebs cycle is allosterically regulated at 4 enzymes1) citrate synthase 2) Isocitrate dehydrogenase 3) -ketoglutarate dehydrogenase4) Malate dehydrogenase

REGULATING THE KREBS CYCLE Krebs cycle is allosterically regulated at 4 enzymes1) citrate synthase 2) Isocitrate dehydrogenase 3) -ketoglutarate dehydrogenase4) Malate dehydrogenase

All are inhibited by NADH& products

Environmental factors 1) Temperature• Rate ~ doubles for each 10˚ C increase up to ~ 40˚ • At higher T start to denature

Environmental factors 1) Temperature• Rate ~ doubles for each 10˚ C increase up to ~ 40˚ • At higher T start to denature

2) pO2

• Respiration declines if pO2 <5%

Environmental factors 1) Temperature• Rate ~ doubles for each 10˚ C increase up to ~ 40˚ • At higher T start to denature

2) pO2

• Respiration declines if pO2 <5%• Problem for flooded roots

Environmental factors 1) Temperature• Rate ~ doubles for each 10˚ C increase up to ~ 40˚ • At higher T start to denature

2) pO2

• Respiration declines if pO2 <5%• Problem for flooded roots

3) pCO2

• Inhibits respiration at 3%

Environmental factors 1) Temperature• Rate ~ doubles for each 10˚ C increase up to ~ 40˚ • At higher T start to denature

2) pO2

• Respiration declines if pO2 <5%• Problem for flooded roots

3) pCO2

• Inhibits respiration at 3%• No obvious effects at 700 ppm, yet biomass reduced

Mineral NutritionStudied by soil-free culture in nutrient solutions:

Mineral NutritionStudied by soil-free culture in nutrient solutions: Hoagland’s is best known

Mineral NutritionSoil-free culture• Sand culture: don’t really control nutrients

Mineral NutritionSoil-free culture• Sand culture: don’t really control nutrients• Hydroponics: immerse roots in nutrient solution

Mineral NutritionSoil-free culture• Sand culture: don’t really control nutrients• Hydroponics: immerse roots in nutrient solution

• Rapidly deplete nutrients & O2 & alter pH

Mineral NutritionSoil-free culture• Sand culture: don’t really control nutrients• Hydroponics: immerse roots in nutrient solution

• Rapidly deplete nutrients & O2 & alter pH• Slanted film maintains [nutrients] & O2

Mineral NutritionSoil-free culture• Sand culture• Hydroponics: immerse roots in nutrient solution• Slanted film maintains [nutrients] & O2

• Aeroponics sprays nutrient solution on roots

Mineral NutritionMacronutrients• CHOPKNS