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

Suppression it in transgenic plant is not essential for plant survival

Metabolic redundancy

NAD+-dependent

matrix of Mito.

NADP+ME in cytosol

GTP in animal

p. 264

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

Replenish the intermediates of TCA cycle, anaplerotic

PEP carboxylase and malate dehydrogenase

Export too much

Replenish malate via

Plant, Cell and Environment (1988) 11: 445

Bypass e- transport chain

Specific inhibitors: rotenone, complex I; antimycin, complexIII ; Cyanide, azide, CO, complexIV ; salicylhydroxamic acid, AOX

(Lowering ATP production)

Five additional enzymes (green)

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

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?

WebEssay 11.4

Some species, such as the arum lilies, are so intensely thermogenic that their flowers can increase up to 35°C above the surroundings. For example, in Brazil, the inflorescence of Philodendron selloum is capable of warming to over 40°C 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.