Respiration Biological process whereby the energy stored in

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 + 6 O 2 + 6 H 2 O (glucose) 1 mole glucose 6 CO 2 + 12 H 2 O + energy (ATP) 36 ATP

Efficiency of Aerobic Respiration • ADP-P bond releases -7. 6 kcal/mol ATP when bond is broken • Theoretical energy yield from burning 1 mol glucose in a calorimeter = -686 kcal/mol • Practical yield from burning 1 mol of glucose in the cell with oxygen = 36 ATP § 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 1 mol glucose in a calorimeter = -686 kcal/mol • Practical yield from burning 1 mol 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 2 goes on to TCA cycle § without O 2 pyruvate is converted to lactate or ethanol (fermentation) • Yields 2 ATP/mole glucose in the absence of O 2

Glycolysis Glucose (6 C) 2 Pyruvate (3 C) CO 2 -O 2 +O 2 Ethanol Lactate TCA Cycle

TCA cycle

Electron Transport System NADH and FADH 2 e- H+ ATP e- H+ 4 e- + 4 H+ + O 2 2 H 2 O cyt. oxidase

Chemiosmotic model H+ H+ H+ H+ Ion concentration difference represents a source of free energy

Chemiosmotic model 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 (6 C) into 2 pyruvates (3 C) • TCA Cycle § mitochondrial matrix § only if oxygen present § converts pyruvate via acetyl Co. A into CO 2; generates NADH and FADH 2 • Electron Transport Chain § mitochondrial membranes = cristae § transfers electrons from NADH and FADH 2 to reduce O 2 to H 2 O and generate ATP

Mitochondria • Spherical to oval § about 1 micron diameter § # mito. /cell increases with demand for respiration; 300 -1000/root tip cell cristae • Double-membrane bound § outer smooth § inner folds forming cristae w controls movement in/out w site of electron transportm • Matrix matrix § soluble phase § site of TCA cycle; DNA, RNA, ribosomes

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 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 25 C • Q 10 = rate of process at one temperature divided by the rate at 10 C lower temp. § Decreases with most plant tissues at 30 -35 C w O 2 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 2 also inhibits ethylene synthesis • Temps. typically about -1 to -0. 5 C • 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 w overflow for electrons when resp. rate exceeds demand for ATP; high with high carbo. levels § Skunk cabbage, Voodoo lily, Stinking lily: CNres. pathway causes temp. of spadix to increase 10 -20 C. w volatilization of odiferous cmpds which attract pollinators