Chapter 11 Respiration and lipid metabolism

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Chapter 11 Respiration and lipid metabolism
(Aerobic) respiration reduced organic
compounds (glucose) are oxidized to release free
energy and generate carbon precursors
for biosynthesis In plant cells, reduced
carbon is derived from sucrose,
hexose phosphates, triose phosphates, fructans,
lipids, organic acids, proteins.
From a chemical standpoint, plant
respiration C12H22O11 12 O2 ? 12 CO2
11 H2O
? photosynthesis
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Suppression it in transgenic plant? is not
essential for plant survival ? Metabolic
redundancy
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p. 264
NAD-dependent matrix of Mito.
NADPME in cytosol
GTP in animal
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NAD malic enzyme ? make possible the complete
net oxidation of TCA cycle intermediates (A)
malate (B) citrate ? to regulate the level of
organic acids in the cells, during fruit ripening
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Replenish the intermediates of TCA cycle,
anaplerotic ? PEP carboxylase and malate
dehydrogenase
Replenish malate via
Export too much
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Plant, Cell and Environment (1988) 11 445
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Five additional enzymes (green)
(Lowering ATP production)
Bypass e- transport chain Specific inhibitors
rotenone, complex I antimycin, complexIII
Cyanide, azide, CO, complexIV salicylhydroxamic
acid, AOX
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Alternative respiration (p. 272-273)
alternative oxidase involved the alternative
oxidase is a quinol-oxygen oxidoreductase
catalyzes a reduction oxygen to water,
and it does not pump protons complexes III
and IV are bypassed, energy conservation in the
form of ATP is much smaller when the AOX
is active is insensitive to cyanide, azide,
or carbon monoxide is inhibited by
salicylhydroxamic acid the AOX pathway
appears particularly active in thermogenic
flowers and it is primarily responsible
for heat production salicylic acid
initiates this thermogenesis is induced by a
variety of stresses, many of which can
inhibit mitochondria respiration
Voodoo lily putrid odor
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The possible function of alternative respiration
1. Heat production in certain membranes of the
Araceae (the arum family) 2. In most plants, to
adjust the relative rates of ATP production and
synthesis of carbon skeletons for use in
biosynthetic reactions alternative oxidase
is regulated by a. reversible
oxidation/reduction of an intermolecular
sulfhydryl bridge b. the reduction level
of the ubiquinone pool c. pyruvate, the
substrate of the TCA cycle 3. To prevent a
potential overreduction of the ubiquinone pool,
which can led to generation of destructive
reactive oxygen species (ROS).
Plastoquinone in chloroplasts RNS?
Why plant mitochondria require both alternative
oxidase and uncoupling protein mechanisms?
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WebEssay 11.4 Some species, such as the arum
lilies, are so intensely thermogenic that their
flowers can increase up to 35C above the
surroundings. For example, in Brazil, the
inflorescence of Philodendron selloum is capable
of warming to over 40C at air temperatures close
to freezing (Figure 1)
Thermal image of the inflorescence of
Philodendron selloum during thermogenesis. The
warm spadix is visible, because the spathe
(V-shaped structure) has been cut away. Sterile
male florets in the center of the spadix are
warmest, but the fertile male florets also
produce heat. Female florets at the base of the
spadix do not produce significant heat.