Feb. 3rd, 2011B4730/5730

Plant Physiological Ecology

Respiration I

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

Leipner et al Env. Exp. Bot. 1999 Maize

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

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d

di

m

RAJ

RAJC

Ag

Hedera helix; Pons et al J Exp Bot 2009

Many species; Sc= surface area of chloroplasts exposed to intercellular airspace; Evans et al J Exp Bot 2009

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

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

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

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

Kruse et al New Phyt 2011

Philodendron bipinnatifidum Miller et al New Phyt 2010

Alternative respiration white; Gray total respiration

Cucumis sativus; Juszcuk et al Phys Plant 2007 MSC16 mutant with lowered respiration/growth rates encoded by mitochondrial genome

Arabidopsis thaliana; Sweetlove et al PNAS 06ucp1 mutant without uncoupling protein