feb. 3rd, 2011 b4730/5730 plant physiological ecology respiration i
TRANSCRIPT
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Feb. 3rd, 2011B4730/5730
Plant Physiological Ecology
Respiration I
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Fs is steady state Fluorescence (F’)Closed circle F’m amb CO2Closed triangle Fs amb CO2Open circle F’m elev CO2Open triangle Fs elev CO2
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Leipner et al Env. Exp. Bot. 1999 Maize
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Mesophyll conductance• Flux of CO2 to stroma (Cc) limited by gs, gm
and gb
• Recent work has shown gm to be variable and important– Low gm reduces CC underestimate VCmax
• Cc=Ci-A/gm
– Estimate gm with curve fitting
• Estime gm with fluorescence and A
)(4
)(8*
d
di
m
RAJ
RAJC
Ag
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Hedera helix; Pons et al J Exp Bot 2009
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Many species; Sc= surface area of chloroplasts exposed to intercellular airspace; Evans et al J Exp Bot 2009
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Limitations to the Farquhar/Fluorescence model of
Photosynthesis• No gene expression controls
– Connection to hormones, whole plant controls– Longer time scales
• Stomatal physiology almost a black box
• Scale of leaf patchiness violates homogeneity
• Light dynamics problematic
• Respiration models are crude
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Autotrophic Respiration
• Can not describe plant growth from photosynthesis only – High N requirements for enzymes of both
• Total Respiration is the sum of – Maintenance
– Growth– Transport
• All eukaryotes with mitochondria have cytochrome respiratory pathway– Inhibited by cyanide
– Plants have cyanide resistant pathway that uses AOX
– animal regulation before glycolysis, plants during
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Autotrophic Respiration• Respiration can be regulated by energy
demand or substrate supply– Photosynthesis and respiration connected
through chemiosmosis (AOX)
• Ratio of CO2 to O2 (respiratory quotient) varies with tissue type and substrates used– <1 more reduced substrates – >1 more reduced products
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Alternative Respiration Pathway• Alternative Respiration pathway (CN resistant)
– Respiration production exceeds demand, reactive oxygen species (ROS) activated
– Uses alternative oxidase (AOX) instead of cytochrome electron transport chain
– Generates heat– Various hypotheses about regulation and purpose
• Uncoupling proteins (UCP) connect to photosynthesis– Uncoupling proteins relieve excess pH gradient in
mitochondria– Photorespiration inhibited by loss of UCP, ROS
problems
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Kruse et al New Phyt 2011
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Philodendron bipinnatifidum Miller et al New Phyt 2010
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Alternative respiration white; Gray total respiration
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Cucumis sativus; Juszcuk et al Phys Plant 2007 MSC16 mutant with lowered respiration/growth rates encoded by mitochondrial genome
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Arabidopsis thaliana; Sweetlove et al PNAS 06ucp1 mutant without uncoupling protein
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