Plant Physiology Exam 4 Study Guide Accumulation and partitioning of photosynthesis starch and sucrose fate of triose phosphates produced as a result of the CalvinBenson cycle? remain in chloroplast or exported to cytosol in either site they are converted to hexose (6C) sugars hexose sugars are used for either starch (chloroplast) or sucrose (cyDon't forget about the age old question of finance homework solutions
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tosol) synthesis (or respiration or growth) Starch synthesis begins with hexose phosphate pools produced by the PCR (CB) cycle (regen phase) Fructose6phosphate is converted to glucose1 phosphate isomerase…. Synthesized into the stroma of plastids in 2 principle structures amylose (linear glucose polymer with alpha 1, 4 linkages) and amylopectin (branched chain structure with alpha 1, 6 linkages) used only as a carbon storage form (big piles of sugar) Interconversion of hexose phosphates Sucrose synthesis synthesized from the hexose phosphate pool primarily through two enzymesSucrose phosphate synthase, sucrose phosphate synthetase Triose Phosphate Utilization can also be used for starch synthesis in the chloroplasts of leaves synthesis of sucrose and starch compete for carbon and is regulated by FBPase heavy regulation keeps synthesis of sucrose in sync with the use of sucrose if it builds up, then hexose phosphates build up, then FBPase builds up and slow down synthesis, causing triose phosphates to build up, and then more carbon goes to starch and then to sucrose again accumultaion of sugars and storage compounds begin to reduce photosynthesis through biochemical feedback – sink limited plants 4/3/17 Phloem Translocation Patterns Sugars are only flowing away from regions of the plant which are adding sugar to the phloem and towards regions removing sugar from the phloem The phloem is a cell itself to things moving around inside them have to be small enough to move inside them All tissues connected to the same phloem strand compete for the sugars Carbon sink metabolism produces a carbon deficit in the cell; must import from elsewhere in the plantYounger leaves are dependent on sugar imports from the phloem; slowly transition to being independent and export sugars Sugar sink strength depends on temperature differences, proximity of sink to source Some have very fixed connections between a specific leaf and root, sectoring 1 leaf and 1 root will be rigidly connected for resource sharing and if one dies the other will too Biotic interaction of phloem parasites They have to be a really strong sink so that they can get they nutrients out (have to compete with host to pull stuff out the (phloem) Insects create galls by reprogramming leaf tissues (or other) to become a huge sink and remove sugar from the phloem Aphid experiment researchers took off some of the growing points on a plant and the plant became much more susceptible to aphids bc they weren’t able to create as many good sinks Respiration Primary vs secondary metabolism Primary core pathways, universal compounds in all species Secondary still produce common compounds, variations in pathways, some species specific products, usually nonessential Everything plants use that contains carbons comes from the same core processesMajor environemental factors affect respiration Oxygen restriction fermentation reactions (wastefully use up NADH) Alcoholic fermentation pyruvate is converted to acetaldehyde and then ethanol Lactic acid fermentation pyruvate is converted to lactate These fermentations yield toxic compounds when they build up, and have wasted and inefficient energy (about 4% of optimal processes) CO2 Excess Pasteur Effect Oxygen concentration decreases limit the ETC which limits CO2 release; around 3%, respiratory CO2 release is at a minimum, and below that fermentation begins Temperature enzymes can be damaged or denatured from temps that are too high or low Daily photosynthetic yield you use ~30% per day just for metabolism, etc. Respiratory rates also change with development Young developing plants(or tissues) have high respiration rates to support building of new tissue Older plants only need respiration to maintain already existence tissues As plants age, physiological activity declines, and respiration rates decline 4/7/2017 Nitrogen AssimilationDifferent than uptake in that it has to be incorporated (mineral nutrients into organisms substances) Ammonia can be assimilated into amino acids, but most of what plants uptake (NO3), they have to change its redox state Nitrogen in the environment nitrate, ammonium, amino acids, nitrogen oxides Nitrate reduction is first stored in the vacuole where it can act as an osmolyte (helps regulate (passively) the pH in the vacuole), up to 15% of the energy expended by plants on metabolism is devoted to this activity Two step process of reduction: (nitrate reduction to nitrite) NO3 + NAD(P)H + H+ + 2 e NO → 2 + NAD(P)+ + H2O (nitrite reduction to ammonium) NO2 + 6 Fdred + 8 H+ + 6 e NH → 4+ + 6 Fdox + 2 H2O This can occur in roots, shoots, or plants, and can vary depending on environment Tightly regulated Protein synthesis nitrate, light in leaves, carbohydrates Reversible phosphorylation light/dark (only active during the day), carbohydrates, energy status of cell Protein degradation rapid turnover Ammonium AssimilationAdded to a C molecule to produce Nitrate reduction to nitrite Nitrite reduction to ammonium Shikimic acid pathway – glyphosate toxicity to plants (Roundup weed killer), by breaking down amino acids Stops them from making new proteins, causing them to eventually starve 4/10/17 Tropisms Phototropism auxin identified as the mobile signal that moved from the tip to the coleoptile (first ID of hormone in plants for long range signal transduction) Auxin triggers acidification of cell walls, allowing expansion In acidic pH, cell wall expansion requires expansin proteins (found in cell wall) loosens the wall and creates turgor pressure 4/12/17 Gravity Perception Theories in Plant Growth Gravitropism= plant perception and reaction to directional response of gravity StarchStatolith theory starch granules are heavy enough to fall through cytoplasm to the bottom part (floor) of the cellAuxin inhibits cell elongation on sides of shoot to coordinate growth at development (coleoptiles, roots) Phytohormone How to regulate active hormone quantity: Biosynthesis Temporary conversion to active form Degradation Transport PLANT PHYSIOLOGY 4010/6010 Outline of material covered for 4th exam (this is not comprehensive but should give you a view of where we have been and guide you in your studying) Products of photosynthetic carbon metabolism: Starch and sucrose (Ch 8) 1. Starch synthesis—insoluble carbohydrate a. Cellular/organelle location of synthesis(CB cycle in stroma of chloroplast, hexose phosphates exported to plastid, forms starch granule that keeps growing) b. Biochemical pathway i. Enzymes(hexose-phosphate isomerase & phosphoglucomutase, ADP-glucose pyrophosphorylase) ii. Substrates(fructose-6-phosphate, glucose-1-phosphate, ATP) iii. Products(glucose-1-phosphate, ADP-glucose) c. Starch types structure i. Amylose(linear/smaller) ii. Amylopectin(branched chain/larger) d. Starch as a storage carbohydrate i. Short-term diurnal storage in chloroplasts(transitory in leaves bc its stored in day then broken down and exported and used at night) ii. Long-term seasonal storage in amyloplasts(parts of the year have higher/lower light intensities and starch is built up during highlight seasons for use in low light seasons)2. Sucrose synthesis from triose phosphates a. Cellular location(carbon exported from chloroplast to cytosol where its synthesized) b. Biochemical pathway i. Enzymes(Pi/triose phosphate transporter, sucrose phosphate synthase, sucrose phosphate phosphatase) ii. Substrates(G3P or DHAP from chloroplast, fructose-1,6- biphosphate,) iii. Products(fructose-1,6-biphosphate, glucose-1-phosphate) c. Metabolic regulation of sucrose synthesis i. Triose phosphate:inorganic phosphate ratios(photosynthesis produces triose phosphate, sucrose has to be used or sent away (or used for starch synthetization) to keep on pace with the triose phosphate as a byproduct of CB) ii. Fructose-2,6-bisphosphate as a regulatory metabolite to suppress formation of Fructose-6-phosphate(FBPase helps regulate the balance btwn sucrose and starch synthesis, and F 2,6-BP is a regulator metabolite that can inhibit it when necessary) d. Regulation of sucrose versus starch synthesis i. Starch accumulation in leaves is reduced by: (when more carbon is being used to make and use sucrose, starch is not made or used) 1. hexose sugar demand by cell (cell growth, etc, requiring high energy use) 2. Sucrose export to phloem(cells sending sucrose to other parts of plants that are growing, etc, the cell still needs to be making more) ii. Chloroplast membrane triose phosphate:inorganic phosphate antiporter is a regulator of the balance between sucrose and starch synthesis Phloem translocation: long distance transport in the phloem (Ch 11) 1. Phloem anatomy a. Cell types i. Sieve elements (sieve tube elements in angiosperms and sieve cells in gymnosperms) ii. Missing organelles iii. Unique cell components(sieve tube damage- callose in sieve pores is deposited btwn PM and cell wall, sealing them off from surrounding contact tissues) b. Companion cells i. Specialized function(connected to its sieve cell by numerous plasmodesmata allowing rapid exchange of solutes, take over some metabolic functions for sieve cells curing differentiation or damage, and the numerous mitochondria in them likely help supply the sieve cells) c. Transfer cells/intermediate cellsi. Role during loading/unloading(transfer cells occur most frequently at nodes in path phloem and phloem unloading pathways, and transport sugars from apoplast to symplast of sieve and companion cells)(intermediary cells have lots of plasmodesmata connecting them to bundle sheath cells, and function in symplastic transport of sugars from mesophyll cells to sieve elements) ii. Anatomical specialization (wall folds/plasmodesmata number) (transfer cells have PM ingrowths that increase surface area to increase potential for solute transfer, with little to no plasmodesmata connections to any cells other than its sieve cell)(intermediary cells have tons of plasmodesmata connecting to surrounding cells (bundle sheath cells, mesophyll cells, and their connecting sieve cells) d. Phloem is continuous cytoplasmic space i. Many cells end to end with connected cytoplasm ii. Sieve plates iii. Large plasmodesmata 2. Special methods used to study phloem transport a. Aphid stylets i. Avoiding plugging of phloem after puncture(avoids blockage by p-proteins and doesn’t wound surrounding tissue) ii. Allowed measurement of contents and demonstrated phloem is pressurized(can remove aphid and leave the stylet, it true and pure phloem sap will come out) b. Radioactive tracers i. Demonstrated phloem as the primary path of movement out of leaves(inserted radioactive glucose into leaves and watched it be transported through phloem, mediated by sieve cells) ii. Calculations of movement rates (velocity or mass transfer rate) 3. Phloem sap contents a. Sugars b. Reduced nitrogen compounds (amino acids, others) c. Inorganic nutrients d. Hormones/signaling compounds 4. Osmotically generated pressure flow is the mechanism of phloem movement (pressure gradient between source and sink to speed up flow) a. At source (sugar, then water, then phloem phluid) i. Sugar loading into phloem makes solute potential more negative ii. Water is drawn to low water potential cell iii. Water intake increases pressure iv. Phloem fluid flows to regions of low pressure, carrying dissolved material by bulk flow. b. At sink (sugar is removed and used, leaving room for more phluid to move into cells) i. Removal of sugar from phloem makes solute potential less negative ii. Water is lost from phloem, reducing pressure c. Patterns of phloem movementi. Phloem sap only flows FROM regions adding sugar to phloem (source) ii. Phloem sap only flows TO regions removing sugar from phloem (sink) iii. Three mechanisms of phloem loading 1. Passive (apoplastic – btwn mesophyll cells and phloem cells) 2. Active (symplastic) 3. Passive polymer trap (symplastic using intermediary companion cells) iv. Phloem unloading mechanism 5. Phloem sink competition (depends on location of sink relative to source and vascular connections between source and sink) 6. Determinants of sink strength (the ability of a sink to mobilize photosynthates towards itself = sink size * sink activity) 7. Distribution of molecules around plant is limited by the vascular connections and whether the tissue is a sink or a source for the phloem Respiration in plants (Ch 12 not lipid metabolism) 1. Overview-dual roles a. Primary vs. secondary metabolism (primary- core pathways, universal compounds, secondary- common compounds, variations in pathways, usually nonessential) 2. Energy production a. Glycolysis(cytosol and plastids- yields ATP, NADH from oxidizing sugars) b. Pentose Phosphate pathway ( cytosol and plastids- yields NADPH and sugar phosphates) c. Citric acid cycle (mitochondrial matrix- pyruvate oxidized to CO2 using lots of reducing power and some energy from sucrose) d. Oxidative phosphorylation (mitochondria- uses ETC to transfer of e from NADH to oxygen, and synthesizing ATP) e. ATP synthesis 3. Energy bypasses that reduce energy yield a. AOX (alternative oxidase- energy released from oxidation of NADH is released as heat, not conserved. This likely helps the plant reduce oxidative stresses and heat themselves which helps attract some pollinators) b. Uncoupling proteins (increase permeability and allow proton flow back into the matrix, preventing buildup of the electrochemical proton gradient, reducing ATP synthesis but not the rate of electron transfer) c. NADP(H) Dehydrogenases (use extra NADH and add electrons to the system is Complex 1 is limiting, is less efficient bc of a skipped step) 4. Environmental regulation of respiration a. Oxygen (flooding) (water filling the air spaces in soil reduces the plants ability to take oxygen into roots, meaning it has to be transported there from higher parts of the plant)i. Fermentative metabolism (alcoholic fermentation-pyruvate converted to acetaldehyde to ethanol, lactic acid fermentation pyruvate converted to lactate, both use up NADH to generate NAD+, which is needed in glycolysis- these are not efficient and some products can be damaging) b. Carbon Dioxide(some soils have excess) c. Temperature (respiration rate and energy use greatly increases with temperature, using 30-60% of daily photosynthetic yield. Can also affect growth and development, nutrient uptake, and ripening and senescence) 5. Developmental regulation of respiration a. Biosynthesis (plants synthesize all 20 amino acids, partially from the citric acid cycle) b. Incomplete oxidation of sugars c. Use of respiratory metabolites for building other molecules—examples i. Cellulose ii. Nucleotides iii. Amino acid synthesis (N assimilation)(incorporation of the nutrient into a form usable by the organism- usually means changing nitrate to ammonium) Nitrogen Reduction and Assimilation (Ch 13 nitrogen only) 1. Uptake vs assimilation (uptake- getting the raw particles containing needed elements into the plant; assimilation- turning the nutrients into usable forms for the plant) 2. Nitrate reduction to nitrite (first step) a. Enzymes (Nitrate Reductase) b. Energy (reduces highly oxidized nitrate to nitrite) c. Regulation (affected by protein concentration, light levels in leaf, carbohydrate availability, only happens in light due to reversible phosphorylation) d. Location (root and/or shoot, in cytosol) 3. Nitrite reduction to ammonium (second step) a. Enzymes (Nitrite Reductase) b. Energetics i. Potential for use of light reactions reductants for nitrite reduction (reduced ferrodoxin from photosynthesis is used by nitrite reductase) c. Location (nitrite is immediately processed bc of toxicity, is moved from cytosol to chloroplasts to be reduced) 4. Assimilation of ammonium and the synthesis of amino acids a. GS/GOGAT cycle (glutamine synthetase / glutamate synthase cycle converts ammonium to ammonia, allowing it to be truly assimilated) b. Transamination reactions (transfer amino groups from one molecule to another- use glutamine to synthesize the other needed amino acids) 5. Glyphosate mode of action (RoundUp weed killa) a. EPSP synthase (prevents synthesis of 3 essential amino acids – phenylalanine, tyrosine, tryptophan)b. Development glyphosate resistant plants (genes contain a copy of EPSPS enzyme that’s naturally unaffected by glyphosate) Plant behavior and hormone biology (Ch 15 for core, pulling from Chs 16-19) 1. Plant behavior (particularly movements) raised questions of mechanisms 2. Plant movements: a. Tropisms (permanent growth in response to a stimulus- new leaf growth facing optimal sunlight direction) b. Nastisms (temporary movement in response to stimuli- leaf rolling for metabolic reasons, leaf closing in venus fly traps) 3. What stimuli can plants perceive? (light, gravity) a. How do plants perceive environmental stimuli? b. Where in plant? (tip of growing coleoptile) c. What is perception mechanism?(blue light) 4. How do plants respond to environmental stimuli? a. Where in plant? (coleoptile tip) b. What is the response mechanism? (auxin redistribution) c. If the location of response is different that location of perception how is this information transmitted/transduced (apoplastically to cells with Rs) 5. Study of plant behavior led to discovery of auxin a. Example of phototropism i. Identification of site of perception (coleoptile tip) ii. Identification of response mechanism (auxin redistribution) iii. Evidence of auxin redistribution as triggering directional response (acidification of cell walls allow expansion) iv. Auxin and the loosening of cellulose fibers in cell walls to allow expansion growth. b. Example of gravitropism i. Identification of site of perception in roots (root cap) ii. Identification of response mechanism in roots (auxin) iii. Evidence of auxin redistribution as triggering the directional response 6. Example of differential effect of hormones in different tissues 7. Auxin promotes cell elongation in shoots 8. Auxin inhibits cell elongation in roots 9. Hormone concepts a. Definition of a hormone b. Roles of hormones c. Hormone action is dependent upon i. Dose of active hormone ii. Sensitivity of tissues (competence to respond) d. Regulation of active levels of hormones i. Synthesis/degradation ii. Activation/inactivationiii. Sequestration/release iv. Uptake/efflux e. Current Major Hormones i. Auxin ii. Gibberellic Acid iii. Cytokinin iv. Abscisic Acid v. Ethylene vi. Brassinosteroids vii. Strigolactone viii. Jasmonic Acid ix. Salicylic Acid f. For each of the major hormones i. Where in the plant is it synthesized? ii. How is it transported around the plant iii. What are the major physiological/developmental effects of the hormone?