C4 and CAM photosynthesis Adaptations that reduce PR & water loss Both fix CO2 with a different enzyme later release CO2 to be fixed by rubisco use energy to increase [CO2] at rubisco C4 isolates rubisco spatially (e.g. corn) CAM isolates rubisco temporally (e.g. cacti)

Crassulacean acid metabolism (CAM) Can tell by d13C rubisco discriminates against 13C, so C3 plants have d13C of -280/00 if it can choose CAM & C4 have d13C of -140/00 because although use up most CO2 in leaf 13C diffuses more slowly Can tell if sugar came from C3 or C4/CAM by d13C Also tells about stomatal opening &water use efficiency

Photosynthesis in the real world Sun leaves: thicker, more PSII, protein & xanthophyll light compensation pt: more cells = more mito Shade leaves: thinner, more PSI & chl, > chlb/chla

Plants and Temperature Affects enzymes: too slow if cold, denature if too hot Rubisco activase is very T sensitive; way to limit PR?

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 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 -> rubisco usually limits C3

Plants and Temperature Heat dissipation Long wave-length radiation Sensible heat loss Conduction & convection to cool air Evaporation

Plant Respiration Recovers energy stored by photosynthesis C6H12O6 + 6 O2 <=> 6 CO2 + 6 H2O + energy Occurs in all plant tissues: even source leaves in light! Releases 50% of fixed CO2

Plant Respiration Releases 50% of fixed CO2 Provides energy for all sinks, source leaves at night & helps source during day!

Plant Respiration Similar, but more complex than in animals Making precursors, recycling products, releasing energy are also important

Plant Respiration Glycolysis in cytosol Pyruvate oxidation in mito Krebs cycle in mito Electron transport & chemiosmosis in mito

Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Unique features in plants May start with DHAP from cp instead of glucose

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

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

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

Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Anaerobic plants ferment pyr to regenerate NAD+ Form EtOH

Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Anaerobic plants ferment pyr to regenerate NAD+ Form EtOH Less toxic than lactate because diffuses away

Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products

Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products Many ways to feed in other substrates to burn

Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis

Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going

Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going Malic enzyme is key: lets cell burn malate or citrate from other sources

Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going Malic enzyme is key: lets cell burn malate or citrate from other sources PEPCarboxylase lets cell replace Krebs intermediates used for synthesis

Plant Respiration Pentose 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 Respiration Pentose phosphate shunt in cytosol or cp makes NADPH & intermediates Uses many Calvin Cycle enzymes

Plant Respiration Pentose phosphate shunt in cytosol or cp makes NADPH & intermediates Uses many Calvin Cycle enzymes Makes nucleotide & phenolic precursors

Plant Respiration Uses many Calvin Cycle enzymes Makes nucleotide & phenolic precursors Gets Calvin cycle started at dawn

ATP generation 2 stages 1) e- transport 2) 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- transport Plants have additional enzymes! NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+

e- transport Plants have additional 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 Much lower affinity for NADH than complex I Energy is released as heat

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! Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+

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

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 lilies 25˚ 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! 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! 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

Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis Generate heat

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

Additional e- transport enzymes! 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!