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Plant F&F - Final
plant form and function final exam material
| Question | Answer |
|---|---|
| Four Major Classes of Organic Compounds: 1)Carbohydrates a. Monosaccharides | (1 sugar)-> "simple sugars" - Glucose - Fructose |
| Four Major Classes of Organic Compounds: 1)Carbohydrates b. Disaccharides | (2 sugars) - Sucrose = 1 Glu + 1 Fru * Primary form in which carbohydrates are transported in the phloem of plants |
| Four Major Classes of Organic Compounds: 1)Carbohydrates c. Polysaccharides | (> 2 sugars) - Starch * Polymer of glucose; Primary form of carbs in which plants store energy* - Fructans - Cellulose |
| Two forms of starch | i)Amylose = un-branched ii) Amylopectin = branched |
| Characteristics of Cellulose | * Primary component of cell walls in plants * Polymer of glucose *1st most abundant organic compound on Earth! |
| Four Major Classes of Organic Compounds: 2)Lipids | - hydrophobic - Lipids in plants are in the form of oils found in seeds and fruits. - have some functions in organisms... |
| Functions of Lipids in Organisms | a. Energy storage b. Cell Membrane Structure (ex. phospholipids) c. "Protection" from herbivores and drying out * cutin (leaves & stems) * suberin(cork cells in periderm & casparian strips of endoderm) * waxes (cuticle) |
| Four Major Classes of Organic Compounds: 3)Proteins | - Composed of amino acids * ~20 different amino acids common to all living organisms * chain of many amino acids = polypeptide chain - each protein has a unique amino acid sequence - and some functions in organisms |
| Functions of the unique amino acid sequences | - determines the way the protein will fold into a unique structure - structure affects the protein's function |
| Functions of Proteins in Organisms | a. Enzymes (help chemical reactions occur in organisms) b. Structural Materials c. Transport Materials |
| Four Major Classes of Organic Compounds: 4)Nucleic Acids | - Nucleotides = the building blocks of nucleic acids - Nucleotides have 3 components: 1. sugar 2. phosphate 3. nitrogenous bases (A,T,C,G) - Functions in organisms |
| Functions of Nucleic Acids in Organisms | - store and translate heritable (genetic) information - also ATP or Adenosine TriPhosphate ATP ADP |
| Secondary Metabolites (chemicals) | - "secondary" = not necessary for life of plant (not part of primary structure or primary metabolic processes) - once thought to be waste products but are important for... *Herbivore Defense *Allelopathy |
| Allelopathy | - chemical compounds from one plant which affect growth of other plants |
| 3 Major Classes of Secondary Metabolites | 1)Alkaloids 2)Terpenoids 3)Phenolics |
| 1) Alkaloids | - Structure: ring structures containing Nitrogen - Ex: Morphine(poppy), Cocaine(cocoa), Caffeine(coffee), Nicotine(tobacco) **All of which are psychoactive and addictive drugs** |
| 2) Terpenoids | - largest class of secondary metabolites - composed of isoprene units - many are poisonous (ex. cardiac glycosides are capable of causing heart attacks) - other examples: *taxol (pacific yew plants: cancer treatment) *rubber |
| Rubber | - high # of isoprene units joined (> 400 units) - found in latex of laticifers |
| 3) Phenolics | - aromatic compounds (C rings with double bonds) - some example groups: * phenolic acids * flavonoids * tannins * lignins |
| Phenolics: - phenolic acids | *ubiquitous (produced by many plants) examples: - salicylic acids - ferulic acid - asprin - etc... |
| Phenolics: - flavonoids | * pigments in vacuoles of some plant cells Examples: - Anthocyanins *up regulation *changing color in leaves during the Fall |
| Phenolics: - tannins | *Deter feeding of herbivores bad taste and interfere with digestion (?) |
| Phenolics: - lignins | *strengthens cell walls -> xylem -> 2' xylem *second most abundant organic compound *structure is unknown |
| Plant cells: Major cells regions | 1) cell wall 2) plasma membrane 3) nucleus 4) cytoplasm |
| (1)The Cell Wall | - Rigid (supports and determines shape and size) - Chemical composition - Our view of cell walls has changed with recent research - Wall Formation - Wall Layers |
| (1)The Cell Wall: Chemical composition and structure (varies in tissue type, species, and layers) | Carbs. 1) Cellulose #1 = "rods" imbedded in matrix of #2 & #3 below * macro/microfibrils 2) Hemicelluloses 3) Pectins Proteins 4) Lignin 5) Enzymes and glycoproteins Lipids 6) Cutin, suberin, and waxes -> reduce wate |
| (1)The Cell Wall: Wall Formation | *components are made INSIDE the cell then, they are exported and deposited on the surface |
| (1)The Cell Wall: Wall Layers | 1)middle lamella-cements primary walls of adj. cells together (high pectin concentration) 2)primary wall (constantly being secreted as the cell gets larger 3)secondary wall ... |
| Wall Layers: Secondary Wall | *is formed after the cell stops growing in size *not present in all cells *interior to the primary cell wall *often has higher concentration of cellulose than the primary wall *may lack pectins and proteins |
| Wall Layers: Secondary Wall | *often 3 distinct layers that differ in cellulose orientation |
| (2)Plasma Membrane | - phospholipid bilayer - fluid mosaic model of membrane structure *proteins "float" in a phospholipid "sea" - several types of proteins assoc. with the plasma membrane: * receptor * recognition * passive/active transporters |
| (4)Cytoplasm | = the cytosol + various organelles *the cytosol: -continuous between cells in plants held together by Plasmodesmata -approx. 85-90% water -plasmodesmata are very common and abundant -plasmodesmata functions: *cell to cell transport. *commun |
| (4)Cytoplasm The cytosol | *because interior of all cells are connected, we can identify: -symplast = the interior of cells, including their plasmodesmata connections -apoplast = the cell walls and intercellular spaces outside the plasma membrane |
| (4)Cytoplasm | Some important organelles and other "structures" in the cytoplasm are: 1)Vacuoles 2)Plastids 3)Mitochondria 4)ER: Endoplasmic Reticulum 5)Ribosomes 6)Dictyosomes (aka. golgi bodies) 7)Cytoskeletons 8)Oil bodies 9)Peroxisomes |
| Vacuoles | -plant cells typically have a large central vacuole -vacuoles are also important for: *storage (food, inorganic nutrients, secondary toxic metabolites to avoid damage *pigments (ampycyans) *degredation ("digestion") |
| Plastids: A)Chloroplasts | *Chloroplasts -internally,thylakoids (a system of membranes inside chloroplast organs) -2 thylakoid types: 1)Grana (stacks of coins) 2)Stroma thylokoids/lamellae (run between the stacks) |
| Plastids: A)Chloroplasts cont'd | -2 aqueous compartments: 1)Stroma (outside) ->thylakoids are in the stroma 2)Lumen (inside the thylakopid space) B)Chromoplasts C) Leucoplasts |
| Mitochondria | -function in energy production through respiration = the "power plants" of the cell (same as in animals) |
| Endoplasmic Reticulum "ER" | = "tunnels" or "pipes" through cytoplasm -involved in transportation and modification of newly formed proteins, as well as other functions |
| Ribosomes | -small structures involved in protein synthesis -often illustrated as "dots" on rough ER ("smooth" ER has no ribosomes) |
| Dicytosomes (aka. Golgi Bodies) | -function in synthesis, packing, and secretion of wall polysaccharides (cellulose, pectin, and hemocellulose) |
| Cytoskeleton | -system of tiny "threads" ->Microfilaments, and tiny "tubes" ->Microtubules; within the cytoplasm -gives cells their overall shape -organizes and moves organelles within the cell |
| Oil bodies | -function in energy storage, especially in seeds and fruits |
| Peroxisomes | page 46 |
| Aerobic Respiration | -part of process occurs in the cytoplasm then moves to the Mitochondria -Overall Reaction: C6H12O6 + 6 O2 ->6 CO2 + 6 H2O (+ ATP) -energy released during breakdown of glucose (and other compounds) -released energy is transformed to ATP |
| Aerobic Respiration 3 stages | 3 stages: 1)Glycolysis -produces only 2ATP (cytoplasm) 2)Krebs Cycle -produces only 2 ATP (mito.) 3)ETC: Electron Transport Phosphorylation -the electron carriers NADH and FADH2 release electrons to a series of molecules with O2 as TEA |
| Aerobic Respiration | 1)Glycolysis = 2 ATP 2)Pyruvate Oxidation = 0 3)Krebs cycle = 2 ATP 4)ETC = 32 ATP ~Typical E. yield: 36 ATP total |
| 2 major stages of Photosynthesis | 1)Energy-transduction reactions (aka.light-dependent reactions) -light energy->ATP + NADPH (e- carrier) -water split -> O2 |
| 2 major stages of Photosynthesis | 2)Carbon-fixation reactions (aka.light-independent reactions) -usually do not occur in the light but have the ability to. CO2 (from air) ->organic compounds |
| Photosystems | 2 photosystems involved in energy-transduction reactions: Photosystems I & II -> mostly work together = assemblages of pigments (chlorophyll & carotinoids) in the thylakoid membranes ~250-400 pigments per photosystem |
| Photosystems cont'd | -organized into an antenna complex and a reaction center -In reaction center: "special chlorophyll-A molecules" ->P700 (in PI) ->P680 (in PII) |
| Energy-Transduction Reactions | -When P700 or P680 absorb energy, they are "boosted" to a higher Energy level -Photosystem I and II work together in "Z-scheme" |
| Energy-Transduction Reactions: P680 | -When P680 gives up electrons to electron acceptors, it replaces its electrons byh "stealing" them from water = Photolysis 2 H2O ->4e-, 4H+, O2 Photolysis = light-dependent splitting of H2O molecules |
| Energy-Transduction Reactions: P680 | P680 -In process, H+ is released into the lumen (inside stacks) -Cytochrome b/f complex of electron transport chain further adds to H+ gradient -H+ gradient powers photophosphorylation |
| Energy-Transduction Reactions: P700 | -When P700 moves to excited states and gives up electrons, its electrons are replaced by accepting them from chain from PI. aka."linear" or "non-cyclic" e- flow -Photosystem I passes electrons down chain, final acceptor = NADP+ -> NADPH |
| Energy-Transduction Reactions: Cyclic Flow | -cyclic flow also possible: (Fd)Ferredoxin sends e-'s back to cytochrome b6/f complex instead of following the chain->cyclic system -Note: (1)H+ gradient still generated & ATP still formed, (2)No NADPH formed |
| Energy-Transduction Reactions: Carbon-fixation | The Calvin Cycle -occurs in stroma of the chloroplast (outside of thylakoids) - 3 stages: 1)fixation 2)reduction 3)regeneration |
| Conversions of PGAL | a) When PGAL remains in the chloroplast -> converted to starch b) Transported out of chloroplast (and into cytosol) -> converted to sucrose |
| Rubisco and Photorespiration | -Rubisco = Ribulose 1,5-bisphosphate (a) carboxylase/ (b) oxygenase *light-activated enzyme *confined to bundle sheath cells |
| Rubisco and Photorespiration | -Photorespiration – a process that, like respiration, uses O2 and releases CO2, but unlike cellular respiration it does NOT generate usable energy -> wasteful & counterproductive process for plants. |
| Rubisco and Photorespiration cont’d | -When O2 is accepted by Rubisco, phosphoglycolate is produces -> “salvage pathway” |
| Rubisco and Photorespiration cont’d | -Why do plants have photorespiration? 1)Rubisco evolution in low O2 environment (oxygenase is not very active trait) 2)Some evidence that photorespiration may be “good” in conditions of high light levels |
| Rubisco and Photorespiration cont’d | -When is photorespiration most evident? 1) [O2] >>[CO2] 2)High temperature environments |
| Rubisco and Photorespiration cont’d | -Metabolic modifications to avoid/minimize photorespiration: (1) C4 photosynthesis *avoids photorespiration by spatial separation of the steps of photosynthesis *eudicots + tropical grasses (crabgrass), sedges, zea mays (corn) |
| Types of C4 Photosynthesis | a) carbon fixation in the mesophyll cells b) malate or aspartate transported to bundle sheath cells c) decarboxylation in bundle sheath cells (Asp->OAA) ->Malate -> pyruvate + CO2 ->pyruvate back to mesophyll cells -> PEP |
| Rubisco and Photorespiration cont’d | (2) CAM photosynthesis ->common in dessert succulent plants, etc. *avoids photorespiration by temporal separation of the steps of photosynthesis a) Fix carbon at night (stomates open at night) b) Release CO2 during day (stomates close in daytime |
| External Factors and Plant Growth | *Response to the external environment involves: Perception of stimulus -> communication to other plant parts -> response |
| Tropisms | (A) General Definition- tropism = growth response where a part of a plant bends/curves toward or away from an external stimulus (aka. Directional Growth Response) -Negative = away from the stimulus -Positive = toward a stimulus |
| Tropisms | (B) Gravitropism- 1) Perception 2)Communication 3)Response |
| Gravitropism: 1) Perception | *one likely possibility = amyloplasts (starch containing plastids) *within roots = located in root cap *within shoots = often located in cells near or around the vascular tissue |
| Gravitropism: 1) Perception | *the “starch-statolith hypothesis” – starch-containing amyloplasts act as statoliths |
| Gravitropism: 2) Communication | *may involve auxin redistribution *recent studies also indicate that Calcium plays an important role |
| Gravitropism: 3) Response | *roots show -> Positive Gravitropism *shoots show -> Negative Gravitropism |
| (C) Phototropism | 1) P = light receptor – pigment called “Zeaxanthin” (a xanthophylls – type carotinoid) 2) C = auxin- rate of transport is altered (> Auxin to the shaded side) |
| Phototropism cont'd | 3) R = auxin causes cells on shaded side to elongate; “bending” toward light = differential growth response |
| (D) Heliotropism “solar tracking” | -leaves and/or flowers move diurnally with respect to direction of sun’s rays Ex. sunflowers track sun throughout the day -Pulvini @ bottom of leaflets -2 types |
| 2 types of Heliotropism | 1) diaheliotropism- perpendicular to sun’s rays (hi SA, > photosynthesis) 2) paraheliotropism – parallel to sun’s rays (lo SA, <photosynthesis) |
| (E) Thigmotropism | Touch-directional growth response Ex. tendrils attaching to pole or other plant (wraps around to continue; bending toward the stimulus) |
| Nastic Movements | = “plant movements that occur in response to a stimulus but whose direction of movement is independent of the position of the origin of the stimulus” |
| Examples of Nastic Movements | 1) Thigmonastic movements = “sensitive plants” like venus fly trap, response of plant movement (rapid) as a result of a mechanical touch stimulus. 2)Nyctinastic movements = “night closure” leaves close at night |
| Daily and Seasonal Patterns of Environmental Response A) Circadian rhythms | = regular, ~ 24hour cycles -Ex. nyctinastic movements, production of some “hormones”, rate of cell division, photosynthesis, etc. |
| Environmental Response A) Circadian rhythms | - evidence that the basic rhythm is endogenous, but that external factors are used to remain synchronized (phytochrome may play a role in this) |
| Environmental Response B) Photoperiodism | -response to changing daylength that occurs seasonally -Flowering Ex. = short-day (d 8hr, n 16 hr); long-day (d 16hr, n 8hr), day-neutral plants (flower at anytime without respect of length of days |
| Environmental Response B) Photoperiodism | one part of the explanation of photoperiodism = phytochrome (Pr = red, Pfr = far red) - sunlight contains both red and far red wavelengths, so during day: Pr ≈ Pfr - in darkness: < Pr and < Pfr |
| Stress Physiology of Plants: A) General Information | - stress = any external factor acting on an organism which brings about a negative response - when are plants under stress? -> all the time; when any optimal conditions are not present |
| B) Example stresses: | 1)Temperature 5)Pollutants/toxins 2)Water 6)UV light 3)Mechanical 7)Nutrient 4)Anaerobosis 8)Parasites/pathogens 9)Allelopathy |
| Temperature Stress | -too high, heat stress -Low, chilling stress - too low, freezing stress |
| Water Stress | - high, flooding stress - low, drought stress |
| Mechanical Stress | - touch, wind, rain, physical stress |
| Anaerobosis Stress | -goes along with flooding |
| Pollutant/toxin Stress | - contamination of air, soil, and water |
| UV light Stress | - related to the depletion of Stratospheric Ozone |
| Nutrient Stress | < nutrient uptake ability, < nutrient availability |
| Parasites/pathogen Stress | -reduce growth, secondary death, damaged caused |
| Allelopathic Stress | - chemicals from one plant influencing surrounding plants |
| C) Generalized stress responses in plants | -evidenced that stresses of many (all?) types bring about similar responses in plants |
| The common features that may be part of a generalized stress response: | * changes in “Hormone” ratios * increase in ABA, decrease in cytokinins * decline in growth rate and in rate of resource acquisition |
| D) Details of some specific stress examples | 1) Heat Stress 4) Drought Stress 2) Chilling Stress 5) Mechanical Stress 3) Freezing Stress 6) Allelopathic Stress |
| 1) Heat Stress | -if expose plants to higher than normal temp. (but non-lethal), plants can acclimate so that later on they can survive at previously lethal temp.s - an important part of this heat stress response = heat shock proteins (hsp’s), or “chaperone proteins” |
| 1) Heat Stress | - hsp’s induced by many other stresses: drought, salt, pollutants &heavy metals, wounding -some (most?) hsp’s are produced during normal plant growth and development (hsp’s upregulated while under stress) |
| 2) Chilling Stress | - membrane fluidity changes - change in enzyme activity and/or change in production of enzymes - allow the plant to function better at lower temp.s |
| 3) Freezing Stress | - part of acclimation/survive of freezing = cell “dehydration” - carbohydrates in vacuoles -> transported to cell wall dehydrate to make solutes = H2O, causes freezing in cell wall where less damage occurs |
| 4) Drought Stress | - stomates close due to high ABA - increase in osmolytes; lower carbs and AA’s to cause increase of solutes in roots to draw in more H2O |
| 4) Drought Stress | - leaf curling and wilting reduces transpiration rates (water loss) by reducing surface area exposed to sunlight -altered root morphology and increased root/shoot ratio |
| 4) Drought Stress | - more roots and larger SA than shoots -dormancy - rain-reduced roots |
| 5) Mechanical Stress | Thigmomorphogenesis = overall plant growth and development is being influenced by touch |
| - some physical changes observed with “touch” stimuli: | * change in membrane potential: rapid (w/I seconds) * increase ethylene plant growth regulator (PGR) ~ 1hr |
| - some physical changes observed with “touch” stimuli: | *increase in mRNA levels of “touch – induced genes” (TCH genes), including some calmodulin-dependent mRNA’s (protein that binds to Ca = Ca mechanism present) |
| 6) Allelopathic Stress “Chemical Warfare” among plants | -the formal, traditional definition = the process in which a plant releases into the environment an organic compound which inhibits or stimulates the growth of another plant |
| 6) Allelopathic Stress “Chemical Warfare” among plants | - wide range of chemicals produced by plants that have allelopathic potential (Ex. tannins, AA’s, phenols, alcohols) |
| - Variety of ways to get out of the plant and into the surrounding environment | 1) leaching from leaves (rain) 2) decay and leaching from plant litter 3) Exudation from roots 4) Volatition from leaves |
| Large numbers of possible ways that these compounds may affect growth | - membrane affect - water relations - chlorophylls content reduce |
| Large numbers of possible ways that these compounds may affect growth | - photosynthesis decreases - inhibition of protein synthesis and DNA replication - reduced PGR’s = growth is inhibited |
| (E) Interactions of stresses | - Evidenced that exposure to one stress may influence response to subsequent stresses (high heat stress builds resistance to low chilling stress) - Simultaneous exposure to multiple stresses? -> effects unknown |
| (E) Interactions of stresses | - separate dry & wet shoot/ root weights to give more accurate observations rather than only the total weight of plants |
| Plant Growth Regulators (PGR) | - the internal regulation of plant growth and development is accomplished via PGR’s *may be produced in one part of plant and transported to another (= hormones) *may act w/I cell or tissue where produced (active in very low concentrations |
| Examples of types of PGR’s: A) the “BIG 5” | 1) Auxins – Indoleacetic Acid (IAA) 2) Gibberellins 3) Abscisic Acid (ABA) 4) Ethylene 5) Cytokinins |
| B) Other more recent discoveries | 1) Jasmonates 2) Salicylic Acid (SA) 3) Oligosaccarins 4) Brassinosteroids 5) Systemin 6) Nitric oxide |
| Transportation within plants: | - in vascular tissue - through other cells Ex. auxin polar transport in phototrophic response |
| Effects/Responses to PGR’s depend on multiple factors | - concentration - sensitivity of receiving cells - type of receiving cells - presence of other PGR’s |
| Major functions of the BIG 5 | (A) Auxin 1) cell elongation (refer to notes on auxin in phototropism) 2) apical dominance = inhibitory affect on lateral branches that stop lateral shoots from growing - some synthetic herbicides are auxins = READING |
| Major functions of the BIG 5 | (B) Gibberellins 1) Promotes germination of dormant seeds and growth of dormant buds 2) Promotes stem elongation 3) Promotes development of some fruits |
| (B) Gibberellins | 1) Promotes germination of dormant seeds and growth of dormant buds 2) Promotes stem elongation 3) Promotes development of some fruits |
| (C) Abscisic Acid (ABA) | 1) Growth inhibition (counter to Gibberellins) - prevents premature germination 2) Stress resistance -> closes stomates |
| (D) Ethylene | 1) Fruit Ripening- “one bad apple spoils the whole bunch” 2) Promotes senescence (age) and abscission of leaves (fall off) |
| (D) Ethylene | 3) Recent studies have found that ethylene is involved in many aspects of growth and development; cell expansion, growth & germ. of grasses, flower opening/closing, sex of flower, etc. |
| (E) Cytokinins | 1) Bud Activation 2) Delay senescence (counter to Ethylene) |
| The Molecular Basis of PGR action: The major mechanisms | - cell expansion and/or cell division is promoted or suppressed - differential gene expression is triggered |
| The Molecular Basis of PGR action: The major mechanisms | * PGR binds to specific protein receptors on cell membrane -> triggers various response pathways that may also involve 2nd messengers -> various transcription regulators are affected to “turn on” or “turn off” gene expression. |
| The Soil-Plant-Atmosphere Continuum: | - water can exit plant to enter atmosphere through cuticle and lenticels BUT over 90% is lost through the stroma - thus, the driving force for water transport = transpitation (through the stomates) |
| Factors Affecting Transpiration Rates: | 1) Temperature - directly affects opening and closing of stomates (movement of water) - high temp./ evaporation rates double per each 10 degrees increased |
| Factors Affecting Transpiration Rates: | 2) Humidity high = less high evapo./transpiration rates; low = more high transp. Rates 3) Wind/air currents (temp. changes) high wind disturbs boundary layer and sucks more water out |
| Factors Affecting Transpiration Rates: | 4) Internal CO2 concentration -directly affects opening/closing of stomata - this, in turn, is influenced by multiple interacting factors: a) balance between photosynthesis (in.) and respiration (de.) |
| Factors Affecting Transpiration Rates: | b) light (affects photosyn. Changing balance & CO2 levels; temp. in.; stomata o/c due to water stress in. ABA) c) Water status of the plant water stress in. ABA & o/c stomates d) temperatures photosynthesis, influences stomates photorespiration |
| Factors Affecting Transpiration Rates: | e) external CO2 concentrations experimental manipulation in lab |
| Factors Affecting Transpiration Rates: | 5) Circadian rhythms - daily cycles of o/c stomates - internal timing mechanism - environmental factors keep in sync and respond to change |
| Opening/Closing of Stomates | (A) Structure - Guard cells attached to one another - Radial micellation -> Ballopns taped |
| Opening/Closing of Stomates | (B) Stomata open (push on each other) when the guard cells swell with water, and close (relax closed) when water leaves the guard cells |
| Opening/Closing of Stomates | (C) The entry or exit of is a response to changing solute conc. (K & Cl-) - When solutes are pumped into guard cells -> H2O follows in...open; and out = H2O exits...close |
| Opening/Closing of Stomates | (D) Mechanisms for solute concentration changes ABA = open -> Ca -> Cl- /malate open -> K+ open (depolar.) -> H2O -> close |
| Opening/Closing of Stomates | (E) Why necessary to regulate o/c at all times? -plant needs to have openings because it needs CO2 in & O2 out - but having permanently open holes is a problem b/c too much H2O lost |
| Water Transport in the Xylem | (a) Water structure = H-bonded chains of H2O molecules (b) The Cohesion-tension Theory - water is pulled through plants NOT PUSHED - adhesion also important (“cohesion-adhesion-tension theory) |
| Water entry and transport in Roots | A) Most water absorption through root hairs (extensions of epidermis) B) Review Root Anatomy |
| Water entry and transport in Roots | C) Pathways through the root 1)Apoplastic 2)Symplastic 3)Transcellular |
| Pathways through the root: | 1) Apoplastic = moving through cell walls, never into cells (Casparian Strips) 2) Symplastic = moving into cells/cytoplasm and through cell to cell via plasma desmata 3) Transcellular = through root hairs cell to cell |
| Assimilate Transport: -> Sucrose movement | a) Source-to-sink transport in the phloem via the sieve tubes. source = leaves, storage (export) sink = roots, fruits, old leaves, storage (import) |
| Assimilate Transport: -> Sucrose movement | b) Pressure-flow hypothesis *osmotically generated pressure “pushes” the assimilates from source to sinks -sucrose enters (phloem loading) sieve tube at source -> water diffuses into sieve tube from surrounding cells (from exylem) |
| Assimilate Transport: -> Sucrose movement | -sucrose carried passively by water to a sink -sucrose exits (phloem unloading) sieve tube at sink -> water follows sucrose out |
| Assimilate Transport: -> Sucrose movement | c) Phloem Loading - May be apoplastic or symplastic. -Apoplastic loading involves active transport into sieve tubes and companion cells (from cell wall) |
| Assimilate Transport: -> Sucrose movement | *ATP powers a proton pump to create a proton gradient = 1˚ Active Transport *Proton gradient powers the active transport of sucrose = 2˚ Active Transport |
| Assimilate Transport: -> Sucrose movement | -Role of companion cells is debatable, but it is likely that they supply most of the energy needed for the process |
| Assimilate Transport: -> Sucrose movement | -Symplastic loading is uncertain, but is thought to travel inside the cells via plasmodesmata and continue to sieve tube through companion cells |
| Assimilate Transport: -> Sucrose movement | d) Phloem unloading and transport into sink cells -may be apoplastic -actual unloading is thought to be a passive process but... -Energy is likely to be necessary to transport into sink tissues |
| Uptake and Transport of Inorganic Nutrients: -> xylem | a) Most uptake is via root hairs/epidermis OR association with fungi -> mycorhizzae b) Most ions appear to travel through the symplastic pathway and are then transported to rest of plant via xylem (dissolved in water) and carried by mass flow |
| Uptake and Transport of Inorganic Nutrients: -> xylem | c) Evidence suggests that nutrient uptake is by active transport - Energy is required in at least 2 steps: 1) pump across membrane of epidermal cells 2) pump into the vessels of xylem |
| Essential Elements: (A) Macronutrients ( ≥ 1,000 mg/kg) | 1) Nitrogen - important component of amino acids (proteins), nucleotides (DNA/RNA), etc. 2) Phosphorus - ATP, etc. |
| Essential Elements: (A) Macronutrients ( ≥ 1,000 mg/kg) | 3) Potassium - osmotic and ionic balance; guard cell regulation of stomates; enzyme activator |
| Essential Elements: (A) Macronutrients ( ≥ 1,000 mg/kg) | 4) Calcium - component of cell walls, pollen tube growth, stomata movement, 2nd messenger, cell volume control, fertilization, gene regulator, cold acclimation, UV light expression, etc... |
| Essential Elements: (A) Macronutrients ( ≥ 1,000 mg/kg) | 5) Sulfur - component of some amino acids, etc. 6) Magnesium - component of chlorophyll; enzyme activator |
| Essential Elements: (B) Micronutrients ( ≤ 100 mg/kg) | Trace Elements: - Iron, Chlorine, Manganese, Molybdenum, Nickel, Copper, Zinc, Boron |
| Common Nutrient Deficiency Symptoms: | A) Chlorosis = leaves turn yellow because of reduced chlorophyll content B) Necrosis = leaf tissue dying and browning C) Reduced Growth D) Wilted or curled leaves -> under? Or up? |
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