• Energy released is coupled to the synthesis of ATP.

Respiration

• Biological process whereby the energy

stored in carbohydrates from PS is released in a step-wise, controlled manner.

• Energy released is coupled to the synthesis of ATP.

• ATP is essential for plant cell maintenance,

growth and development

Carbohydrate Conversion

• Starch glucose

• Sucrose + water glucose + fructose

Equation for Aerobic Respiration

C ₆ H ₁₂ O ₆ + 6O ₂ + 6H ₂ O 6CO ₂ + 12H ₂ O + energy

(glucose) (ATP)

1 mole glucose 36 ATP

Efficiency of Aerobic Respiration

• ADP-P bond releases -7.6 kcal/mol ATP when bond is broken

• Theoretical energy yield from burning 1mol glucose in a calorimeter = -686 kcal/mol

• Practical yield from burning 1mol of glucose in the cell with oxygen = 36ATP

 36 ATP X -7.6 kcal/mol = -274 kcal/mol glucose

 274/686 kcal/mol X 100 = 40% efficiency

Efficiency of Anaerobic Respiration

• ADP-P bond releases -7.6 kcal/mol ATP when bond is broken

• Theoretical energy yield from burning 1mol glucose in a calorimeter = -686 kcal/mol

• Practical yield from burning 1mol of glucose in the cell without oxygen = 2 ATP

 2 ATP X -7.6 kcal/mol = -15.2 kcal/mol glucose

 15.2/686 kcal/mol X 100 = 2.2% efficiency

3 Stages of Respiration

• Glycolysis

• TCA Cycle

• Electron Transport Chain

Glycolysis

• Occurs in all living organisms

• Only stage which can occur without oxygen

• Oldest stage of respiration

 operated for billions of years in anaerobic organisms

• Converts glucose to 2 pyruvates in cytosol

 with O

goes on to TCA cycle

 without O

pyruvate is converted to lactate or ethanol (fermentation)

• Yields 2ATP/mole glucose in the absence of O ₂

Glycolysis

Glucose (6C)

2 Pyruvate (3C)

Ethanol Lactate

TCA Cycle

CO

+O

-O

-O

TCA

cycle

Electron Transport System

NADH and FADH ₂ e ^-

e ^-

4e ^- + 4H ⁺ + O ₂ 2H ₂ O

cyt. oxidase

H ⁺

H ⁺

ATP

Chemiosmotic model

H ⁺ H ⁺ H ⁺

H ⁺ H ⁺

H ⁺ H ⁺ H ⁺

H ⁺

H ⁺ H ⁺

H ⁺

H ⁺ H ⁺

H ⁺

Ion concentration difference represents a source of

free energy

Chemiosmotic model

H ⁺ H ⁺

H ⁺ H ⁺ H ⁺

H ⁺ H ⁺ H ⁺

H ⁺ H ⁺ H ⁺

H ⁺

H ⁺ H ⁺

H ⁺

The energy represented by the H ⁺ gradient is converted to a

chemical form (ATP) via the ATP synthase

3 Stages of Respiration

• Glycolysis

 cytoplasm

 with or without oxygen present

 breaks glucose (6C) into 2 pyruvates (3C)

• TCA Cycle

 mitochondrial matrix

 only if oxygen present

 converts pyruvate via acetyl CoA into CO

; generates NADH and FADH

• Electron Transport Chain

 mitochondrial membranes = cristae

 transfers electrons from NADH and FADH

to reduce O

to H

O and generate

ATP

Mitochondria

• Spherical to oval

 about 1 micron diameter

 # mito./cell increases with demand for respiration; 300-1000/root tip cell

• Double-membrane bound

 outer smooth

 inner folds forming cristae

 controls movement in/out

 site of electron transportm

• Matrix

 soluble phase

 site of TCA cycle; DNA, RNA, ribosomes

matrix

cristae

Alternate Fates of Glucose C

• Not all C respired to CO ₂

• Intermediates of respiration branch off:

 amino acids

 pentoses for cell wall structure

 nucleotides

 porphyrin biosynthesis

 fatty acid synthesis

 lignin precursors

 precursors for carotenoid synthesis, hormones

Factors Affecting Resp. Rate

• [Substrate]

• [ATP]

• [Oxygen]

• Temperature

• Plant type

• Plant organ

• Plant age

Factors: Substrate Availability

• Resp. higher right after sundown compared to right before sunrise due to [S]

• Shaded leaves respire slower than lighted leaves

• Starvation of plant tissue results in utilization of proteins

• High [ATP] in cell and get negative feedback

on resp.

Factors: [Oxygen]

• No effect until [O ₂ ] < 1%

 Cyt oxidase not sensitive to O ₂ until 0.05%

• O ₂ diffuses in water 10,000 X slower than in air

• Some plants have intercellular air system, e.g., aerenchyma in shoots and roots (rice)

• Very low levels of O ₂ see accelerated breakdown

of sugars to ethanol and CO ₂ evolved = Pasteur

Effect

Factors: Temperature

• Q ₁₀ for respiration is 2.0 - 2.5 between 5 and 25C

• Q ₁₀ = rate of process at one temperature divided by the rate at 10C lower temp.

 Decreases with most plant tissues at 30-35C

 O

being used so fast, it can’t diffuse fast enough into tissues

• Tropical regions - 70-80% PS C lost to resp. due

to high night temperatures and resp. rates

Factors: Plant Type/Organ/Age

• Resp. rate tends to increase with age of plant

 Young trees lose about 1/3 daily PS C to resp. and doubles with older trees as ratio of PS/Non-PS tissue decreases

• Greater metabolic activity = greater resp. rates

 Root tips, dev. buds and meristematic regions in general have higher respiration rates

 In veg. tissues, resp. decreases from the tip to the mature regions

• Seeds - low resp. rates, dormant, desiccation results in

slowdown of respiration

Factors: Plant Type/Organ/Age (cont.)

• Ripening Fruit

 Resp. high when young cells are dividing and growing

• Climacteric Fruit (apples, tomatoes)

 Sharp increase in rate immediately before fruit ripening = climacteric rise in respiration

 Coincides with full ripeness and flavor and preceded by huge increase in ethylene production

 This leads to senescence and decrease in respiration

• Non-climacteric Fruit

 Citrus, cherries, grapes, pineapple, strawberries

 Insensitive to ethylene

Controlled Atmosphere Storage

• Lower O ₂ (2% - 3%) & raise CO ₂ (5% - 10%)

 slows down resp.

• No ethylene

 high CO

also inhibits ethylene synthesis

• Temps. typically about -1 to -0.5C

• Pick apples in Sept./Oct. when green and immature and store in CA

 expose to normal air with ethylene when ready to sell

fresh apples in March

Cyanide Resistant Respiration

• Aerobic resp. (cyt oxidase) in plants and animals inhibited by CN ^- and N ₃ ^- (azide)

 bind to Fe in enzyme and halts e

transport

• Animals: CN causes resp. to decrease fast, virtually irreversible and fatal

• Plants: display a 10-25% CN-resistant resp. and alternate pathway for electron flow

 electron flow branches off to alternate oxidase

 less ATP produced

Cyanide Resistant Respiration (cont.)

• Metabolic Role?

 No clear role

 Operates when cyt oxidase poisoned

 Energy overflow hypothesis

 overflow for electrons when resp. rate exceeds demand for ATP; high with high carbo. levels

 Skunk cabbage, Voodoo lily, Stinking lily: CN-res.

pathway causes temp. of spadix to increase 10-20C.

 volatilization of odiferous cmpds which attract pollinators