L12 Plant Physiology Photosynthesis PDF

Plant Physiology Stephen Hales Module 1 The Father of Plant Physiology Lorrenne C. Caburatan, D.Sc. Ap...

Plant Physiology Stephen Hales Module 1 The Father of Plant Physiology Lorrenne C. Caburatan, D.Sc. Applications of Plant Physiology - Dormancy and germination dynamics - Plant input requirements plus yield - Electron transport blocker - Use of fertilizers; 17 essential elements - Plant photo insensitivity; semi-dwarf rice - Phytohormones for growth, development - Kinetin for flower preservation - Drought resistant varieties; water content - Grain yield under limited water conditions  Photosynthesis Photosynthesis Module 2 Lorrenne C. Caburatan, D.Sc. Credits to: Prof. Djamae Manzanares, M.Sc. Prof. Christina Barazona, M.Sc. Prof. Adrian Gandecila, M.Sc. Photosynthesis Photosynthesis Light-Dependent Reaction of Photosynthesis Photosystems  Light-Dependent Reaction of Photosynthesis Part 1D Photosynthesis: The Electron Transfer Chain Figure 19.22. Pathway of Electron Flow From H2O to NADP+ in Photosynthesis. This endergonic reaction is made possible by the absorption of light by photosystem II (P680) and photosystem I (P700). Abbreviations: Ph, pheophytin; QA and QB, plastoquinone- binding proteins; Pc, plastocyanin; A0 and A1, acceptors of electrons from P700*; Fd, ferredoxin; Mn, manganese. Light-Independent Reaction of Photosynthesis  Light-Independent Reaction of Photosynthesis Calvin Cycle - takes place in the stroma - three basic types of photosynthetic mechanisms: - C3, C4, CAM  Anatomy of C3 and Kranz C4 plants Anatomy of C4 Plants  Single Cell C4 Photosynthetic Plant Single Cell C4 Photosynthesis Selective Protein Import Unique organization of single cell C4 photosynthetic Q: How do genes in dimorphic chloroplasts differentially expressed? mechanisms - Specific recognition process Chloroplasts in peripheral - Preprotein cytoplasmic compartment - Chloroplast import apparatus - Transit peptide - Internal targeting site Chloroplasts in central cytoplasmic compartment Offermann et al. 2011. How do single cell C4 species form dimorphic chloroplasts? Plant Signaling & Behavior 6:5, 762-765 Bienertia sinuspersici Selective mRNA-Targeting Selective Protein Degradation Proteases specifically degrade certain proteins Nuclear encoded mRNA which are not required or which interfere with Ribosomes in close proximity Directional transport – cytoskeleton proper function of the respective chloroplast type C3 C4 Selective mRNA trapping Substrate specificity of chloroplast proteases one type of chloroplast two types of chloroplasts Degradation of mRNAs within distinct regions Differential accumulation of protease Offermann et al. 2011. How do single cell C4 species form dimorphic Offermann et al. 2011. How do single cell C4 species form dimorphic chloroplasts? Plant Signaling & Behavior 6:5, 762-765 chloroplasts? Plant Signaling & Behavior 6:5, 762-765 CAM Photosynthesis chloroplast genome Whole genome The genome of extant chloroplast encode only ~100 proteins. Accordingly, more than 95% of chloroplast protein are nuclear encoded  Thank you! GOD bless! J PLANT RESPIRATION AEROBIC RESPIRATION AEROBIC RESPIRATION RESPIRATION: an overview the direct oxidation of hexose by molecular Higher plants are aerobic organisms, oxygen, with the consequent release of all of 6 the free energy as heat they require the presence of molecular oxygen for normal metabolism. From the energetic perspective, by breaking the oxidation of hexose down into series of They obtain both the energy and small, discrete steps, the release of energy is carbon required for maintenance and also controlled so it can be conserved in growth by oxidizing the metabolically useful forms. photoassimilates. RESPIRATION: an overview RESPIRATION: an overview RESPIRATION: an overview provides carbon skeletons for a number of plant Products are distributed and utilized for plant products, such as: growth and maintenance: Respiration has three (3) major steps: amino acids for proteins, glycolysis, nucleotides for nucleic acids, In growth respiration, energy in the form of ATP, Krebs cycle, and reductants in the form of NADPH/NADH or structural carbon precursors for fats, building blocks of carbon skeletons are used for electron transport system porphyrin pigments, and the synthesis of new plant biomass. (ETS)/electron transport chain (ETC). aromatic compounds (lignin) In maintenance respiration, the products are used for repair and maintenance of existing structural systems (membrane proteins) and for ion gradients which keep mature cells in viable form. OVERVIEW OF CELLULAR SUMMARY OF AEROBIC RESPIRATION MITOCHONDRIA: RESPIRATION IN EUKARYOTIC CELLS structure and function Inner and outer mitochondrial membranes enclose two spaces: the matrix and intermembrane space. The outer mitochondrial membrane serves as its outer boundary. The inner mitochondrial membrane is subdivided into two interconnected domains: Inner boundary membrane Cristae – where the machinery for ATP is located MITOCHONDRIA: structure MITOCHONDRIA: structure MITOCHONDRIA: structure and function Mitochondrial Membranes The outer membrane is about 50%; the inner membrane is more than 75% protein. The inner membrane contains cardiolipin but not cholesterol. (Bacterial membranes contain both though.) The outer membrane contains a large pore- forming protein called porin. The inner membrane is impermeable to even small molecules; the outer membrane is permeable to even some proteins. MITOCHONDRIA: GLYCOLYSIS structure and function GLYCOLYSIS: functions A process that converts sugars to pyruvate and takes place in cytosol where small amount of Leads to formation of molecules that The mitochondrial matrix contains: ATP is synthesized through substrate-level can be removed from the pathway for phosphorylation. synthesis of other compounds a circular DNA molecule, ribosomes, and The ATP synthesis is catalyzed by an enzyme and enzymes. involves the transfer of a phosphate group of an Pyruvate can be oxidized in the Hence, mitochonrdrial RNA and proteins can be organic substrate molecule to ADP. mitochondrion and yield larger ATP synthesized its own matrix. Partial oxidation of hexose (2 molecules of pyruvic amounts acid/hexose) --- 2 molecules of NAD+ is reduced to NADH (+2H+) that uses no O2 and releases no CO2 Produces ATP (hexose is twice phosphorylated by ATP) (net: 2 ATP) GLYCOLYSIS: an overview GLYCOLYSIS The first steps in oxidative metabolism are carried out in glycolysis. Glycolysis produces pyruvate, NADH, and two molecules of ATP. FATES OF Aerobic organisms use O2 to extract more than 30 additional ATPs from pyruvate and PYRUVATE NADH. Pyruvate is transported across the inner membrane and decarboxylated to form acetyl CoA, which enters the next stage. FERMENTATION FERMENTATION TRICARBOXYLIC ACID CYCLE (TCA CYCLE) or KREBS CYCLE The tricarboxylic acid (TCA) cycle: When O2 is limiting: Lactic acid Alcoholic is a stepwise cycle where substrate is oxidized NADH and pyruvate accumulate → Fermentation Fermentation (loss of an electron) and its energy conserved. The two-carbon acetyl group from acetyl CoA is FERMENTATION Glucose Glucose condensed with the four-carbon oxaloacetate to form a 2 Lactic acid 2 Ethanol + 2 Ethanol (alcoholic fermentation) CO2 six-carbon citrate. 2 ADP + Pi 2 Lactic acid (lactic acid fermentation) ATP 2 ADP + Pi 2 Example: in roots growing under waterlogged ATP During the cycle, two carbons are oxidized to CO2, conditions (paddy rice field condition) (catalyzed by: regenerating the four-carbon oxaloacetate needed lactic acid (catalyzed by: to continue the cycle. dehydrogenase) pyruvic acid decarboxylase and alcohol dehydrogenase)  TRICARBOXYLIC ACID CYCLE (TCA CYCLE) TRICARBOXYLIC ACID CYCLE (TCA CYCLE) or KREBS CYCLE or KREBS CYCLE Reaction intermediates in the TCA cycle are Four reactions in the cycle transfer a pair of common compounds generated in other catabolic electrons to NAD+ to form NADH, or to FAD+ reactions making the TCA cycle the central KREB’S to form FADH2. metabolic pathway of the cell. CYCLE One ATP is formed through substrate-level Three molecules of ATP are formed from each phosphorylation when succinyl-CoA is pair of electrons donated by NADH; converted to succinic acid. two molecules of ATP are formed from each pair of electrons donated by FADH2. Why? Best to take note of this at the ETC/ETS process. TRICARBOXYLIC ACID CYCLE (TCA CYCLE) TRICARBOXYLIC ACID CYCLE (TCA CYCLE) TCA CYCLE or KREBS CYCLE: or KREBS CYCLE or KREBS CYCLE functions Reduction of NAD and FAD to electron donor NADH and FADH2 (they are subsequently oxidized to yield ATP during ETS) Direct synthesis of ATP (1 molecule for each pyruvate oxidized) Formation of carbon skeletons for the synthesis of certain amino acids THE ROLE OF MITOCHONDRIA IN THE ELECTRON TRANSPORT SYSTEM/ THE ROLE OF MITOCHONDRIA IN THE FORMATION OF ATP ELECTRON TRANSPORT CHAIN FORMATION OF ATP Electron-Transport Complexes – Complex I (NADH dehydrogenase) catalyzes transfer of Electron Transport electrons from NADH to ubiquinone and transports four H+ per Electrons move through the inner membrane pair. via a series of carriers of decreasing redox – Complex II (succinate dehydrogenase) catalyzes transfer of potential. electrons from succinate to FAD to ubiquinone without transport of H+. Electrons associated with either NADH or – Complex III (cytochrome bc1) catalyzes the transfer of FADH2 are transferred through specific electrons from ubiquinone to cytochrome c and transports four electron carriers that make up the electron H+ per pair. transport chain. – Complex IV (cytochrome c oxidase) catalyzes transfer of electrons to O2 and transports H+ across the inner membrane. – Cytochrome oxidase is a large complex that adds four electrons to O2 to form two molecules of H2O. The metabolic poisons CO, N3–, and CN– bind catalytic sites in Complex IV. THE ROLE OF MITOCHONDRIA IN THE THE ROLE OF MITOCHONDRIA IN THE FORMATION OF ATP FORMATION OF ATP Electron-Transport System (continued) The electrons gradually lose energy as they pass Electron-Transport System (continued) along the chains of electron carriers. The free energy associated with the The released energy pumps H+ into the formation of the proton electrochemical intermembrane space, creating an H+ or pH gradient is called proton motive force. gradient across the membrane. It is harnessed to make ATP from ADP + Pi through ATP synthase, in a process called chemiosmosis. CHEMIOSMOTIC PHOSPHORYLATION CHEMIOSMOTIC PHOSPHORYLATION SUBSTRATE-LEVEL PHOSPHORYLATION The H+ ions diffuse back across the inner membrane by passing though the ATP Oxidative synthase which capture their energy to make phosphorylation Photosynthetic ATP. phosphorylation The cell couples the exergonic reactions of electron transport and endergonic synthesis of ATP. “Chemiosmotic Theory” by P. Mitchell (1966) explains how pH gradient drives the formation of ATP OXIDATIVE METABOLISM IN THE OXIDATIVE PHOSPHORYLATION: summary RESPIRATORY CHAIN INHIBITORS MITOCHONDRION The Importance of Reduced Coenzymes Step 1: High energy electrons are passed from FADH2 or NADH. As electrons move through the electron-transport chain, H+ are pumped out across the inner membrane. Step 2: The controlled movement of protons back across the membrane. ATP is formed by the controlled movement of H+ back across the membrane through the ATP- synthesizing enzyme. Oxidative phosphorylation can be uncoupled from ETS by uncoupling agents like dinitrophenol or inhibited by potent Oxidative phosphorylation - the process when ATP formation is driven by energy that is released from electrons removed during substrate oxidation phosphorylating inhibitors like oligomycin. PLANT AEROBIC RESPIRATION: PLANT AEROBIC RESPIRATION: PLANT AEROBIC RESPIRATION: unique features unique features unique features In Krebs Cycle: In Electron-Transport System: The succinyl-coA synthetase step produces The availability of an alternative pathway for ATP instead of GTP which the step the reduction of O2 which leads to cyanide- produces in animals. resistant respiration. Significant NAD+-malic enzyme activity that An external dehydogenase that faces the enables the plant mitochondria to operate an intermembrane space and is capable of alternative pathway for metabolism of PEP oxidizing cystolic NADPH. produced by glycolysis. A rotenone-insensitive NADH dehydrogenase that faces the mitochondrial matrix. BIOENERGETICS OF RESPIRATION BIOENERGETICS OF RESPIRATION OTHER PATHWAYS OF PLANT RESPIRATION For every 1 molecule of hexose: Efficiency of respiration : How much energy on Aerobic respiration is strongly inhibited by certain Glycolysis: 2 NADH glucose can be trapped as ATP? negative ions such as cyanide (CN-), azide (N3-) and 2 ATP = 2 Input: Complete oxidation of a mole of glucose carbon monoxide (CO) ATP Krebs Cycle: 8 NADH at pH 7, -ΔG = 2880 kJ Combined with iron in the cytochrome oxidase (Complex IV) prevents respiration 2 ATP = 2 Output: Hydrolysis of 36 ATP @ 41 kJ = ATP 2 FADH2 36 × 41 = 1476 kJ Cyanide-resistant respiration /Alternative pathway ETS:2 NADH @ 2 ATP = 4 ATP (Glycolysis) (1 mole ATP hydrolyzed releases about 28 – 41 kJ) 8 NADH @ 3 ATP = 24 ATP (Krebs) Efficiency: Output × 100 = 1476 × 100 = 51.25% Pentose phosphate pathway/ Hexose 2 FADH2 @ 2 ATP = 4 ATP monophosphate shunt/ Oxidative pentose (Krebs) Input : 2880 phosphate pathway/ phosphogluconate pathway TOTAL 36 Note: The remaining 48.75% are lost as heat (yes they all mean the same thing, just remember one term) ATP ALTERNATIVE RESPIRATION OR ALTERNATIVE RESPIRATION OR CYANIDE- OTHER PATHWAYS OF PLANT RESPIRATION RESISTANT PATHWAY: functions CYANIDE-RESISTANT PATHWAY Thermogenesis Alternative pathway Electrons from ubiquinone are directly accepted by Energy overflow Key enzyme for O2 via an alternative oxidase. pathway: Alternative Occurs in leaves and roots oxidase (AOD or AOX) Contributes to ATP synthesis when the cytochrome path is saturated (consuming carbohydrates not needed for growth, energy  homodimer that span the inner mitochondrial overflow) membrane, with active side facing the matrix Bulk of heat has thermogenic significance  functions as a ubiquinone O2 oxidoreductase: in pollination that is, it accepts e- from the UQ-pool and Skunk cabbage transfers them directly to oxygen (try to find out why and how this in plant response to low temperatures plant uses the said pathway)  energy that will be conserved as ATP is converted to heat instead OTHER PATHWAYS OF PLANT RESPIRATION OTHER PATHWAYS OF PLANT RESPIRATION OTHER PATHWAYS OF PLANT RESPIRATION Alternative pathway Pentose phosphate pathway Pentose phosphate pathway Thermogenesis Floral development in Araceae (skunk cabbage) Hexose monophosphate shunt; Oxidative pentose NADPH is oxidized to form ATP needed for phosphate pathway; phosphogluconate pathway Tissues of the spadix undergoes a surge in oxygen fatty acid biosynthesis; consumption, called respiratory crisis Pathway from glucose degradation where plants obtain energy from the oxidation of sugars in CO2 Erythrose-4-phosphate as starting compounds Higher temp volatizes amines that attract insect pollinators and H2O for production of phenolic compounds like Electron acceptor: NADP+ instead of NAD+ anthocyanins and lignins Energy flow hypothesis In most tissues the alternative pathway is inoperative until Products: Ribose-5-phosphate as precursor for ribose the normal cytochrome pathway has become saturated NADPH, and deoxyribose units in nucleotides, RNA The rate can be increased by increasing the supply of erythrose-4-Phosphate, and DNA carbohydrates to cells --- excess supply over and above ribose-5-Phosphate what is required for metabolism or processed for storage PENTOSE PHOSPHATE PATHWAY OVERVIEW OF CELLULAR FACTORS AFFECTING RESPIRATION RESPIRATION IN EUKARYOTIC CELLS Functions NADPH Substrate availability – for fatty acid synthesis Oxygen availability Ribose 5- phosphate – for nucleic acid synthesis Temperature Erythrose 4- phosphate – for phenolic Type and Age of Plant compounds synthesis FACTORS AFFECTING RESPIRATION FACTORS AFFECTING RESPIRATION FACTORS AFFECTING RESPIRATION Oxygen Availability Temperature Substrate Availability Variations in the O2 content of air are too small to Plants deficient in sugars or low substrate have Respiration is temperature dependent. influence respiration in leaves/stems. Quantitative measure to describe the effect of temp is the low respiration rates. The rate of O2 penetration in plant organs are usually temperature coefficient or Q10 Substrate starvation → proteins/fats are used. sufficient to maintain normal respiration levels in At temp above 30°C, the Q10 in most plants begin to mitochondria. Respiration rates of leaves are very fast at fall off as substrate availability becomes limiting. In flooded soils where hypoxia (low O2) or anoxia (no O2) The O2 penetrating the cells begin to limit respiration sundown → high sugar levels due to exists → accumulation of photosynthates during the day. at higher temp at which chemical reactions could high CO2 and low ATP yield, with sugar used more as substrate proceed rapidly. – Pasteur effect (practical importance during storage) When temp rises to 40°C, if prolonged, rate Decreasing O2 can minimize aerobic respiration without decreases as a result of enzyme denaturation. stimulating anaerobic respiration. FACTORS AFFECTING RESPIRATION FACTORS AFFECTING RESPIRATION Type and Age of Plant Plants exhibit differences in morphology and Other Factors: External or Internal metabolism → rate differs among various plants and CO2 – often inhibits the process between cells, tissues, and organs Based on what we’ve learned about cellular respiration, how can CO2 inhibit it? Root tips/meristematic tissues have higher respiratory rates on a dry weight basis than non- Wounding – facilitates the entry of O2 or activates metabolic tissues (woody stems) enzymes of respiration Age influences respiration:  Climacteric fruits  Non-climacteric fruits Mechanical stimulus  Apple  Cherry Salt respiration – addition of ions to plants previously High during rapid vegetative growth, declines before flowering  Avocado grown in distilled water stimulates respiration Young leaves, roots, and growing flowers  Citrus During fruit development (ripening); declines when picked  Banana  Pineapple “Climacteric rise”  Mango  Strawberry coincides with the full ripeness and full flavor of fruits  Tomato  Watermelon RESPIRATION: functions RESPIRATION: functions SUBSTRATES FOR RESPIRATION 1. Provides ATP to power most cellular work 2. Provides materials for cellular biosynthesis CARBOHYDRATES PROTEINS LIPIDS : TRIGLYCERIDES (FAT / OIL) (aldose) (ketose) Fat Oil Disaccharides Polysaccharides (animal) (plant) glycosidic bond glycosidic bond (1-4) (1-4) PHYSIOCHEMISTRY OF LIPIDS CONVERSION OF FATS/OILS TO SUGARS CONVERSION OF FATS/OILS TO SUGARS Structurally diverse compounds soluble in organic Key Steps: solvents but insoluble to water 1. In the spherosomes, triglycerides are hydrolyzed to Biosynthesis of fats, oils and other lipids requires fatty acids (FA) and glycerol. large investment of metabolic energy. 2. In the glyoxysome, FA are activated to fatty acyl- CoA which undergoes beta-oxidation and becomes Fatty acid synthesis is localized in the chloroplast acetyl CoA. and proplastids of non-green tissues. 3. The glyoxylate cycle generates succinate that moves Membrane lipids occur in SER and mitochondrial to mitochondrion and is converted to malate. membrane. 4. Malate is oxidized to oxaloacetate, decarboxylated to Fats and oils exist in the form of triglycerides PEP and by reverse glycolysis (gluconeogenesis) in Stored in spherosomes/oleosomes/lipid bodies in plants the cytosol produces glucose → sucrose Why would the plant go through all this trouble? What instance would it choose this? CONVERSION OF FATS/OILS TO SUGARS LIPIDS : PHOSPHOLIPIDS LIPIDS : CUTIN, SUBERIN & WAX Examples of hydroxy lfatty acids that polymerize to make CUTIN HOCH2(CH2)14COOH HOCH2(CH2)8CH(CH2)5COOH CONTROL OF OH RESPIRATION Examples of hydroxyl fatty acids THROUGH that polymerize to make SUBERIN HOCH2(CH2)14COOH HOOC(CH2)14COOH FEEDBACK END OF RESPIRATION Examples of common WAX INHIBITION components CH3(CH2)27CH3 (alkane) CH3(CH2)22COOH (fatty acid) O CH3(CH2)22CO(CH2)25CH3 (ester) CH3(CH2)24CH2OH (alcohol)