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sugar sink

sugar sink


School: Clemson University
Department: Biology
Course: Plant Physiology
Professor: Douglas beilenberg
Term: Spring 2017
Tags: plant, Physiology, Auxin, tropisms, starch, and sucrose
Cost: 25
Name: Exam 4 Study Guide
Description: This includes all of my notes from the powerpoints in lecture and an annotated version of the test outline that he uploaded. This is a Study Guide NOT a week of notes.
Uploaded: 04/14/2017
13 Pages 144 Views 1 Unlocks

What is perception mechanism?

How do plants perceive environmental stimuli?

What stimuli can plants perceive?

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?

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