植物細胞的生長與分化

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(1)Plant Growth . Definition: – Size increase by cell division and enlargement, including synthesis of new cellular material and organization of subcellular organelles.. Growth and Development . Growth – Irreversible change in Mass. . Development – Irreversible change in State Embryogenesis Juvenile Adult. Vegetative Adult Reproductive. 1.

(2) Growth . Components 1. Cell Division 2. Cell Enlargement. MEASURING GROWTH . Increase in fresh weight Increase in dry weight Volume Length Height Surface area. 2.

(3) HOW PLANTS GROW . Meristems – Dicots Apical. meristems – vegetative buds. – shoot tips – axils of leaves Cells. divide/redivide divide/redivide by mitosis/cytokinesis mitosis/cytokinesis Cell division/elongation causes shoot growth Similar meristematic cells at root tips. HOW PLANTS GROW . Meristems (cont) Secondary. growth in woody perennials. – Increase in diameter due to meristematic regions – vascular cambium xylem to inside, phloem to outside – cork cambium external to vascular cambium produces cork in the bark layer. 3.

(4) Cell Division . Meristematic Cells (Stem Cells) Primary – Shoot Apical Meristem (SAM) – Root Apical Meristem (RAM). . Secondary – Axillary Buds – Vascular Cambium – Cork Cambium – Pericycle (root). Cell Enlargement . Adjacent to Meristems Internode growth - Shoot Zone of Elongation - Root Turgor Pressure H2O. Uptake Cell Wall Loosening new cell walls. 4.

(5) Types of Growth . . 1. Determinant Terminal shoot apex flowers 2. Indeterminant Axillary buds flower Terminal buds vegetative 3. Monocarpic Flower once then die 4. Polycarpic Flower repeatedly over several seasons. Types of Growth . . 5. Annual Monocarpic Flower in one season and then die 6. Biennial Monocarpic Flower in second season and then die. 5.

(6) Types of Growth . . 7. Herbaceous Perennial Polycarpic Determinant Flower early and then go dormant Flower Bulbs Indeterminant Flower throughout season Shoot dies in Fall. Types of Growth . . . 8. Woody Perennial Polycarpic Indeterminant flower only once per year Biennial Bearing flower and set fruit every other year Mast Flowering more prolific in some years than in others. 6.

(7) ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH . Light Temperature Water Gases. PLANT GROWTH REGULATORS . 3. Hormone – a. Substance that acts in very low concentration (micro-molar or less) – b. Produced in one part of plant and act in another (translocatable) – c. Has the same response in many different plant species. 7.

(8) PLANT GROWTH REGULATORS . 1. Auxins 2. Cytokinins 3. Gibberellins 4. Abscisic Acid 5. Ethylene. Natural Auxin . 1. Endogenous Indole Acetic Acid. 8.

(9) Synthetic Auxins. Auxin . Synthesis a. Young developing leaves b. Terminal buds, growing axillary buds c. coleoptile tips Transport Basipetal away from tip. . 9.

(10) Auxin Polar Transport. Auxin Action . Mechanism of Action a. Bind Receptor Protein Plasma membrane b. Transport into cell c. Activate ATPase in Plasma membrane d. H+ ion extrusion e. acidify cell wall f. break hemicellulose-pectin bonds g. cellulose microfibrils slide apart h. cell enlarges. 10.

(11) Auxin Cell Wall Loosening. Auxin Responses . Cell Enlargement Shoot Growth Internodes Tubers Bulbs Root Growth Storage Roots Adventicious Roots Fruit Growth Strawberry - Receptacle enlargement Apical Dominance Auxin:Cytokinin Ratio High - Dormant Axillary Buds Low - Axillary Bud Growth. 11.

(12) Auxin Agricultural Uses . . Rooting of Cuttings Propagation Greenhouse and Nursery Crops Hormodin, Hormodin, Rootone, Rootone, etc. Commercial preps of 2,42,4-D Herbicide High Concentration 2,42,4-D Dicots more sensitive Monocots less sensitive Weed control in cereal crop production Prevent Abscission of Leaves and Fruit Older leaves Ripe Fruit Endogenous production of IAA stops Replaced by exogenous NAA. CYTOKININS. (IPA). 12.

(13) Cytokinins . Synthesis – Root Apex. . Transport – Upward in Xylem. Cytokinins . Responses Stimulate Cell Division Apical Dominance High Auxin in Shoot Apex High Cytokinin in Root Apex Gradient Between: High Auxin:Cytokinin Dormant Axillary Buds Low Auxin:Cytokinin Branch Growth. 13.

(14) Cytokinins . . . Synthetic Cytokinins Kinetin DNA degredation Benzyladenine (BA or 6-Benzyl amino purine) Agricultural Uses Limited Induction of Axillary Buds Roses, Chrysanthemum Micropropagation Shoot proliferation in Tissue Culture. Gibberellins . Family of more than 130 structures. 14.

(15) Gibberellins O. C=O. HO. OH. CH3. C CH2 HO. O. GA1. Gibberellins . Inactive. Active. 15.

(16) Gibberellins . Synthesis Tissue Localization – Immature seed embryo, Young Leaves, roots. . Transport – Phloem. Gibberellins . . . Responses Cell Elongation Dwarf cultivars eg. eg. Peas (Little Marvel) Dwarfing rootstocks apples, pears, peaches height from roots fruit quality from scion Seed Dormancy High ABA Reversed by GA application Synthesis of GA by embryo. 16.

(17) Gibberellins. Gibberellins Agricultural . . . Uses. 1. Thompson Seedless Grapes Principal use Parthenocarpic Fruit 2. Seed Germination Malting Barley Precocious germination 3. Male Flower production Monoecious & Dioecious Plants 4. Chilling Requirement Azaleas Biennials Biennial Bearing. 17.

(18) Ethylene. H H. C=C. H H. Ethylene . . C2H4. Gas at room temperature. Synthesis. |ÅHemicellulose +ATP | Methionine ---> ---> SAM ---> ---> ACC ---> ---> Ethylene ---> ---> PG 1 2 | 3 |ÆGalactose . 1. SS-Adenosyl Methionine 2. Amino Cyclo Propane 3. Polygalacturonase. 18.

(19) Ethylene . Agricultural Uses. – Ethaphon - breaks down to form ethylene. . 1. Fruit Ripening Tomato, Banana, Melon, etc. Pick unripe and firm for shipping Spray in store to "ripen" Color development and softening Field Spray Uniform and synchronous ripening Canning Tomatoes Mechanical Harvest. Ethylene . . . 2. Floral Development Bromeliads Pineapple Banana Uniform development of inflorescence 3. Sex Expression Female Flowers Curcubits opposite of GA action 4. Degreening of Citrus Oranges, Lemons, Grapefruit Break down Chlorophyll Leaves Carotenoids. 19.

(20) Ethylene . . 5. Mechanical Harvesting Formation of Abscission Zone Stimulate Fruit Drop Cherries, Walnuts, Pecans 6. Postharvest Shelf Life block ethylene synthesis AgNO3 or Silver Thiosulfate delay senescence Carnations. Abscisic Acid. CH3. O. CH3. CH3. C OH. OH. O. CH3. 20.

(21) Abscisic Acid . . Natural Plant Growth Retardant Opposes action of GA and Auxin Synthesis Chloroplasts Breakdown product of Carotenoids. Abscisic Acid . . . Responses Dormancy Maintenance high levels in dormant seed and buds Drought Resistance causes stomatal closure Agricultural Uses None. 21.

(22) Translocation in the Phloem. Patterns of translocation: Source to Sink Metabolites move from source to sink. SOURCE = area of supply - exporting organs: mature leaves - storage organs: seed endosperm, storage root of second growing season beet SINK = areas of metabolism (or storage) - non-photosynthetic organs and organs that do not produce enough photosynthetic products to support their own growth or storage - Example: roots, tubers, developing fruits/seeds, immature leaves. 1.

(23) Exactly what is transported in phloem?. Sucrose The sugar that is most important in translocation is sucrose Sucrose is a disaccharide, i.e., made up of two sugar molecules – an additional synthesis reaction is required after photosynthesis. Sucrose - is not a rigid structure, but mobile in itself.. http://www.biologie.uni-hamburg.de/b-online/e16/16h.htm#sucr. 2.

(24) Compounds translocated in the phloem. Compounds translocated in the phloem. 3.

(25) Primary phloem and primary xylem Stem of Clover. Phloem Location review. Root Stele. Stem Vascular Bundle. Leaf Midrib. Phloem is always in close proximity to xylem.. 4.

(26) Sieve elements are highly specialized for translocation Longitudinal section. External view. Sieve elements are highly specialized for translocation. 5.

(27) Three different types of companion cells Ordinary companion cells - have chloroplasts - few plasmodesmata between companion cell and surrounding cells, except for own sieve elements - symplast of sieve element and its companion cell is relatively isolated from surrounding cells. Transfer cells - similar to ordinary companion cells - develop fingerlike wall ingrowths, particularly on walls that face away from sieve element - wall ingrowths increase surface area of plasma membrane (increases potential for solute transfer across membrane). Intermediary cells - have numerous plasmodesmata connecting them to bundle sheath cells - have many small vacuoles - poorly developed thylakoids and lack of starch grains. Phloem transport Velocities ≈ 1 m hour-1 , much faster than diffusion. What is the mechanism of phloem transport? What causes flow?, What’s the source of energy?. 6.

(28) General diagram of translocation. Physiological process of loading sucrose into the phloem. Pressure-flow Phloem and xylem are coupled in an osmotic system that transports sucrose and circulates water. Physiological process of unloading sucrose from the phloem into the sink. Sugars are moved from photosynthetic cells and actively (energy) loaded into companion cells. Fig. 10.14. 7.

(29) Sugars are moved from photosynthetic cells and actively (energy) loaded into companion & sieve cells.. The concentrating of sugars in sieve cells drives the osmotic uptake of water.. Fig. 10.14. Fig. 10.16. Phloem loading uses a proton/sucrose symport.. 8.

(30) Pressure- Flow-Hypothesis Munch Hypothesis Source •. High concentration of sucrose, via photosynthesis, –. •. Δ[sucrose] drives diffusion,. Active H+-ATPase, –. electrochemical gradient drives symporters,. •. - Ψs builds, water enters the cell, + Ψp builds.. •. Low concentration of sucrose,. Sink –. Δ[sucrose] drives diffusion,. Active H+-ATPase,. •. –. electrochemical gradient drives antiporters,. – - Ψs drops, water exits the cell, Ψp drops.. Pressure-Flow-Hypothesis. Ψp •. Notice that the Ψs at the source is more negative than at the sink!. •. Why don’t we expect water to flow toward the source?. Water, along with solutes moves down the pressure gradient, not the water potential gradient.. 9.

(31) Water Cycling. Phloem unloading. • Apoplastic: three types • (1) [B] One step, transport from the sieve elementcompanion cell complex to successive sink cells, occurs in the apoplast. • Once sugars are taken back into the symplast of adjoining cells transport is symplastic. 10.

(32) The pressure-flow model (Münch, 1930s). Fig. 10.10. The pressure-flow model of phloem translocation At source end of pathway • Active transport of sugars into sieve cells • Ψs and Ψw decrease • Water flows into sieve cells and turgor increases At sink end of pathway • Unloading of sugars • Ψs and Ψw increase • Water flows out of sieve cells and turgor decreases. 11.

(33) Ψw -1.1MPa. -0.4MPa. 12.

(34) Photosynthesis Overview Energy for all life on Earth ultimately comes from photosynthesis. 6CO2 + 12H2O. C6H12O6 + 6H2O + 6O2. Oxygenic photosynthesis is carried out by: cyanobacteria, 7 groups of algae, all land plants 1. Photosynthesis Overview Photosynthesis is divided into: light-dependent reactions -capture energy from sunlight -make ATP and reduce NADP+ to NADPH carbon fixation reactions -use ATP and NADPH to synthesize organic molecules from CO2 2. 1.

(35) 3. Photosynthesis Overview Photosynthesis takes place in chloroplasts. thylakoid membrane – internal membrane arranged in flattened sacs -contain chlorophyll and other pigments grana – stacks of thylakoid membranes stroma – semiliquid substance surrounding thylakoid membranes 4. 2.

(36) 5. Discovery of Photosynthesis The work of many scientists led to the discovery of how photosynthesis works. Jan Baptista van Helmont (1580-1644) Joseph Priestly (1733-1804) Jan Ingen-Housz (1730-1799) F. F. Blackman (1866-1947) 6. 3.

(37) Discovery of Photosynthesis C. B. van Niel, 1930’s -proposed a general formula: CO2+H2A + light energy CH2O + H2O + 2A where H2A is the electron donor -van Niel identified water as the source of the O2 released from photosynthesis -Robin Hill confirmed van Niel’s proposal that energy from the light reactions fuels carbon fixation 7. Pigments photon: a particle of light -acts as a discrete bundle of energy -energy content of a photon is inversely proportional to the wavelength of the light photoelectric effect: removal of an electron from a molecule by light -occurs when photons transfer energy to electrons 8. 4.

(38) 9. Pigments Pigments: molecules that absorb visible light Each pigment has a characteristic absorption spectrum, the range and efficiency of photons it is capable of absorbing.. 10. 5.

(39) 11. Pigments chlorophyll a – primary pigment in plants and cyanobacteria -absorbs violet-blue and red light chlorophyll b – secondary pigment absorbing light wavelengths that chlorophyll a does not absorb. 12. 6.

(40) Pigments Structure of pigments: porphyrin ring: complex ring structure with alternating double and single bonds -magnesium ion at the center of the ring -photons excite electrons in the ring -electrons are shuttled away from the ring 13. 14. 7.

(41) 15. Pigments accessory pigments: secondary pigments absorbing light wavelengths other than those absorbed by chlorophyll a -increase the range of light wavelengths that can be used in photosynthesis -include: chlorophyll b, carotenoids, phycobiloproteins -carotenoids also act as antioxidants 16. 8.

(42) Photosystem Organization A photosystem consists of 1. an antenna complex of hundreds of accessory pigment molecules 2. a reaction center of one or more chlorophyll a molecules Energy of electrons is transferred through the antenna complex to the reaction center. 17. 18. 9.

(43) Photosystem Organization At the reaction center, the energy from the antenna complex is transferred to chlorophyll a. This energy causes an electron from chlorophyll to become excited. The excited electron is transferred from chlorophyll a to an electron acceptor. Water donates an electron to chlorophyll a to replace the excited electron. 19. 20. 10.

(44) Light-Dependent Reactions Light-dependent reactions occur in 4 stages: 1. primary photoevent – a photon of light is captured by a pigment molecule 2. charge separation – energy is transferred to the reaction center; an excited electron is transferred to an acceptor molecule 3. electron transport – electrons move through carriers to reduce NADP+ 4. chemiosmosis – produces ATP 21. Light-Dependent Reactions In sulfur bacteria, only one photosystem is used for cyclic photophosphorylation 1. an electron joins a proton to produce hydrogen 2. an electron is recycled to chlorophyll -this process drives the chemiosmotic synthesis of ATP. 22. 11.

(45) 23. Light-Dependent Reactions In chloroplasts, two linked photosystems are used in noncyclic photophosphorylation 1. photosystem I -reaction center pigment (P700) with a peak absorption at 700nm 2. photosystem II -reaction center pigment (P680) has a peak absorption at 680nm 24. 12.

(46) Light-Dependent Reactions Photosystem II acts first: -accessory pigments shuttle energy to the P680 reaction center -excited electrons from P680 are transferred to b6-f complex -electron lost from P680 is replaced by an electron released from the splitting of water 25. Light-Dependent Reactions The b6-f complex is a series of electron carriers. -electron carrier molecules are embedded in the thylakoid membrane -protons are pumped into the thylakoid space to form a proton gradient. 26. 13.

(47) Light-Dependent Reactions Photosystem I -receives energy from an antenna complex -energy is shuttled to P700 reaction center -excited electron is transferred to a membrane-bound electron carrier -electrons are used to reduce NADP+ to NADPH -electrons lost from P700 are replaced from the b6-f complex. 27. Light-Dependent Reactions ATP is produced via chemiosmosis. - ATP synthase is embedded in the thylakoid membrane -protons have accumulated in the thylakoid space -protons move into the stroma only through ATP synthase -ATP is produced from ADP + Pi 28. 14.

(48) 29. Carbon Fixation Reactions To build carbohydrates, cells need: 1. energy -ATP from light-dependent reactions 2. reduction potential -NADPH from photosystem I. 30. 15.

(49) Carbon Fixation Reactions Calvin cycle -biochemical pathway that allows for carbon fixation -occurs in the stroma -uses ATP and NADPH as energy sources -incorporates CO2 into organic molecules. 31. Carbon Fixation Reactions carbon fixation – the incorporation of CO2 into organic molecules -occurs in the first step of the Calvin cycle ribulose-bis-phosphate + CO2 5 carbons 1 carbon. 2(PGA) 3 carbons. The reaction is catalyzed by rubisco. 32. 16.

(50) Carbon Fixation Reactions The Calvin cycle has 3 phases: 1. carbon fixation 2 molecules PGA RuBP + CO2 2. reduction PGA is reduced to G3P 3. regeneration of RuBP G3P is used to regenerate RuBP 33. 34. 17.

(51) Carbon Fixation Reactions Glucose is not a direct product of the Calvin cycle. -2 molecules of G3P leave the cycle -each G3P contains 3 carbons -2 G3P are used to produce 1 glucose in reactions in the cytoplasm. 35. Carbon Fixation Reactions During the Calvin cycle, energy is needed. The energy is supplied from: - 18 ATP molecules - 12 NADPH molecules. 36. 18.

(52) Carbon Fixation Reactions The energy cycle: -photosynthesis uses the products of respiration as starting substrates -respiration uses the products of photosynthesis as starting substrates. 37. 38. 19.

(53) Photorespiration Rubisco has 2 enzymatic activities: 1. carboxylation – the addition of CO2 to RuBP -favored under normal conditions 2. photorespiration – the oxidation of RuBP by the addition of O2 -favored in hot conditions CO2 and O2 compete for the active site on RuBP.. 39. 40. 20.

(54) Photorespiration Some plants can avoid photorespiration by using an enzyme other than rubisco. -PEP carboxylase -CO2 is added to phosphoenolpyruvate (PEP) -a 4 carbon compound is produced -CO2 is later released from this 4-carbon compound and used by rubisco in the Calvin cycle 41. Photorespiration C4 plants -use PEP carboxylase to capture CO2 -CO2 is added to PEP in one cell type (mesophyll cell) -the resulting 4-carbon compound is moved into a bundle sheath cell where the CO2 is released and used in the Calvin cycle. 42. 21.

(55) 43. 44. 22.

(56) 45. Photorespiration CAM plants -CO2 is captured at night when stomata are open -PEP carboxylase adds CO2 to PEP to produce a 4 carbon compound -this compound releases CO2 during the day -CO2 is then used by rubisco in the Calvin cycle 46. 23.

(57) 47. 24.

(58) Photosynthesis The Source of most Biological Energy Trapped in Photosynthesis Energy Converted to Chemical Bonds. Light: An Energy Waveform With Particle Properties Too. wavelength violet blue green yellow orange red 400. 500. 600. 700 nm. wavelength (nm) 10-9 meter 0.000000001 meter!. 1.

(59) Light: An Energy Waveform With Particle Properties Too. wavelength visible spectrum 400. 500. 600. 700 nm. wavelength (nm) 10-9 meter 0.000000001 meter!. White Light. Green is reflected!. Leaf Pigments Absorb Most Colors. 2.

(60) Light: An Energy Waveform With Particle Properties Too. amplitude brightness intensity Many metric units for different purposes We will use an easy-to-remember English unit: foot-candle 0 fc = darkness 100 fc = living room 1,000 fc = CT winter day 10,000 fc = June 21, noon, equator, 0 humidity. Photosynthetic Rate. What wavelengths of light drive photosynthesis? 100%. 0. Action Spectrum green light reflected some still drives photosynthesis. 400. visible spectrum 500 600 wavelength (nm). 700 nm Light beyond 700 nm has insufficient energy to drive photosynthesis. 3.

(61) Photosystem II chlorophyll b. Light. P450. lutein An te nn a. en er. P470. gy. zeaxanthin Pi. gm. P480. en t. Co m. er. to: ETS e-. lycopene. from: H2O. tr a. ns f. ß-carotene P500. pl e. In each energy transfer x some energy is lost as heat: 2nd law of thermodynamics.. P510. echlorophyll b. But enough energy is passed to P680 to eject an electron to the electron transport system.. Chlorophyll a. Chlorophyll b. CH2. CH2. HC. CH3. H. HC. P650. chlorophyll a P680. ß-Carotene. HO. CHO. H. Zeaxanthin. CH3 H3C. N. N Mg. H N. H3C. C2H5 H3C H. N. H. CH3. N. C2H5. N Mg. H N. H3C. H N. CH HC C CH3 HC. H3C. CH3. H H2C. H H. CH2 O=COCH O 3 O=C O H2C CH H3C C CH2 H2C CH2 H3C CH CH2 H2C CH2 H3C CH CH2 H2C CH2 HC H3C CH3. H2C. H H. CH2 O=COCH O 3. O=C O H2C CH H3C C CH2 H2C CH2 H3C CH CH2 H2C CH2 H3C CH CH2 H2C CH2 HC H3C CH3. Photosynthetic pigments are amphipathic. CH3. CH3. CH3 CH HC C CH3 HC. H3C. CH HC C CH3 HC. CH HC C CH3 HC. CH HC CH H3C C CH HC CH H3C C CH HC CH3 H3C. CH HC CH H3C C CH HC CH H3C C CH HC CH3 H3C. H3C. H3C OH. Lutein. 4.

(62) 100%. What intensities of light drive photosynthesis?. Reaction Rate. Photosynthesis. add to reserve grow reproduce Respiration. Using reserves and may die. 0. 0 10. 100. compensation point. 1,000. 10,000 fc. Light Intensity (fc). The example plant shown here “breaks even” at an intensity we have in our homes…a house plant!. 100%. What intensities of light drive photosynthesis?. Reaction Rate. Photosynthesis A. 0. Photosynthesis B. Respiration. Shade tolerant plant dies in intense light!. 0 10. 100. compensation points. 1,000. 10,000 fc. Light Intensity (fc). The second example plant shown here cannot survive in our homes…it is a sun-loving crop plant!. 5.

(63) The Light Reactions: An Energy Diagram -2.0. reducing. P700* FeS. -1.5. Fd FNR. -1.0 Em (volts). PQ ATP 2 H2O. 1.0 1.5 2.0. cyt b. Pheo. 0 0.5. NADP+ NADPH. P680*. -0.5. eH+. cyt f PC ADP+Pi. 4 eO2 + 4 H+. oxidizing. P700 PS I. P680 PS II. The PCR Cycle has Three Phases P-C-C-C-C-C-P CO2 ribulose-1,5bisphosphate rubisco carboxylation ADP C-C-C-P 3-phosphoglycerate. regeneration. ATP. sucrose for transport starch for storage. reduction C-C-C-P glyceraldehyde3-phosphate. ATP NADPH NADP+ ADP + Pi. 6.

(64) Let’s Do Some Stoichiometry: 3 P-C-C-C-C-C-P CO2 3 x 5 = 15 C 3 ribulose-1,5bisphosphate rubisco carboxylation 3 ADP 6 C-C-C-P 3-phosphoglycerate 6 3 ATP ATP 6 reduction NADPH 5 5 x 3 = 15 C 6 6 C-C-C-P NADP+ To take off 3 carbons: glyceraldehyde- 6 ADP + P sucrose for transport 6 i 3-phosphate 1 starch for storage regeneration complex shuffling. More Stoichiometry:. 3 ADP. 3 P-C-C-C-C-C-P CO2 3 ribulose-1,5bisphosphate rubisco carboxylation. 6 C-C-C-P 3-phosphoglycerate sucrose and 6 starch are not ATP 6 reduction 3-carbon NADPH 5 compounds! 6 6 C-C-C-P NADP+ To take off 3 carbons: glyceraldehyde- 6 ADP + Pi 6 sucrose for transport 3-phosphate 1 starch for storage 3 ATP. regeneration complex shuffling. 7.

(65) The PCR Cycle and Light Reactions are interdependent. H2O. O2. Light Reactions thylakoid. chlorophyll, etc. ADP + Pi NADP+ PCR Cycle. NADPH ATP. rubisco, etc.. stroma. CO2. (CH2O)3. The PCR Cycle cannot operate in darkness! “Dark Reactions?”. RuBisCO: an ancient enzyme with a modern problem RuBP + CO2. RuBisCO. 1% in air O=C=O. RuBP + O2 20% in air O=O. 2 x P-C-C-C (Phosphoglycerate) RuBisCO often constitutes up to 50% of the protein in a plant…to ensure enough photosynthesis is achieved. RuBisCO. P-C-C-C (a Phosphoglycerate) + P-C-C 2 x CO2 photorespiration. • Early in evolution of photosynthesis the atmosphere was anaerobic, so RuBisCo evolved without a problem. • As photosynthesis was successful, competitive inhibition from oxygen was essentially a negative feedback. • Evolution has not yet replaced RuBisCO. • But several workarounds have evolved…. 8.

(66) C4 Photosynthesis: The first fixation is a 4-carbon compound Mesophyll Cell. Bundle Sheath Cell. regeneration C3 acid. phosphoenol pyruvate. HCO3pepc. plasmodesmata. C3 acid. C4 acid. PCR cycle rubisco CO2 decarboxylation C4 acid. carboxylation atm CO2. C4. The C4 and C3 reactions are spatially separated. Zea mays. Leaves bundle sheath mesophyll. PEPc expression in leaf cs http://botit.botany.wisc.edu/images/130/Leaf/Zea_leaf_cross_section/ Major_vein_MC.jpg http://www.conabio.gob.mx/malezasdemexico/a steraceae/flaveria-trinervia/imagenes/rama.jpg. RubisCO expression in leaf cs. Flaveria bidentis http://www.uni-duesseldorf.de/home/Jahrbuch/2002/Grieshaber/Grafik/Grieshaber05.gif. http://wings.buffalo.edu/academic/department/fnsm/ bio-sci/facultyart.GIFS/Berryart.gif. 9.

(67) Zea mays leaf cross section showing classic Kranz anatomy. Zea mays leaf cross section These bulliform cells lose water and the leaf rolls…which way?. 10.

(68) C4 Photosynthesis: A cycle requiring ATP and NADPH. NADP malic enzyme type Bundle Sheath Cell. Mesophyll Cell ADP. ATP pyruvatephopsphate dikinase. CCCOOpyruvate plasmodesmata. P CCCOOphosphoenol pyruvate -. HCO3 pepc. Pi. NADP+. CCCCOOoxaloacetate. PCR cycle rubisco. NADPH malic enzyme NADP+. -OOCCCCOOmalate malate dehydrogenase. carbonic anhydrase. atm CO2. NADPH. CCCOOpyruvate. CO2. -OOCCCCOOmalate. The C4 and C3 reactions are spatially separated. CAM Photosynthesis: Crassulacean Acid Metabolism At Night. In Daylight. starch triose phosphate phosphoenol pyruvate. low pH. HCO3-. malic acid. higher pH. NADPH. pepc NAD+. malate. NADH malic oxaloacetate dehydrogenase. atm CO2. starch PCR cycle pyruvate rubisco CO2. malic acid. malic enzyme NADP+ malate. stomata open! stomata closed! The C4 and C3 reactions are temporally separated. 11.

(69) Sedum leaf cross-section (a CAM plant)Note the lack of palisade/spongy differentiation. Sedum leaf cross-section (a CAM plant)Note the lack of Kranz anatomy. 12.

(70)