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chapter 13 outline

by: Caitrín Hall

chapter 13 outline BIOL 1110

Caitrín Hall
GPA 3.9

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About this Document

These notes cover chapter 13 lecture and textbook material.
Introduction to Botany
Bernard Goffinet
Class Notes
Biology, botany, outline
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This 5 page Class Notes was uploaded by Caitrín Hall on Tuesday January 26, 2016. The Class Notes belongs to BIOL 1110 at University of Connecticut taught by Bernard Goffinet in Summer 2015. Since its upload, it has received 14 views. For similar materials see Introduction to Botany in Biology at University of Connecticut.

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Date Created: 01/26/16
Plant Behavior 13.1 Plants sense and respond to external and internal stimuli  Abiotic signals – external and physical o Light, temperature, pressure, gravity  Biotic signals – originate from other organisms or from within organism’s body  Signal transduction – process by which signals are transmitted from reception point to response site o Proteins bind to hormones or undergo physical change (become activated) in response to physical signals o Begins when activated receptor molecules cause chemical changes in cytoplasmic messenger molecules (often—addition of phosphate group) o Chemical signal is passed along signal transduction pathway o Stimuli often cause release of ions such as calcium-binding proteins or change in gene expression 13.2 Hormones regulate plant growth and development Hormones – chemical compounds produced in one part of body & exert effects on another Plant growth substances – plant hormones  Auxins, cytokinins, gibberellins, ethylene, abscisic acid, brassinosteroids, systemin, salicylic acid, jasmonic acid  Chemical structures determine functions  Auxins o Fruit production o Produced from amino acid tryptophan in young leaves  shoot apex  Induce leaf/flower growth at shoot apex  Induce cells to secrete acid into cell walls, causing them to loosen  Induce development of vascular tissue—creates path for auxin transport to lower regions of plant  Apical dominance (retards lateral bud growth immediately below)  Results from high demand for sugar by active shoot tip; not  enough sugar left for axillary buds; new branches form when  shoot tip is removed  Mediate growth response to light direction  Promote activity of secondary meristems  Induce formation of roots  Inhibit leaf and fruit drop  Stimulate ethylene synthesis  Cytokinins o Used with auxins to clone plants in labs (tissue culture – pieces of stem,  leaf, or root are removed) o Auxin + cytokinin = 10:1  plant cells divide to form a callus o Auxin + cytokinin > 10:1  callus forms roots o Auxin + cytokinin < 10:1  callus turns green/develops shoots o Derived from adenine o Produced primarily in root tips o Transported through xylem to meristems, seeds, leaves, fruit o Work by inducing mitosis in shoot and root meristems o Activate secondary meristems & production of adventitious roots o Form partnerships between roots and good bacteria o Delay leaf aging  Gibberellins o Produced by terpene synthesis pathway in apical buds, roots, leaves, embryos o Promotes stem/leaf elongation by stimulating mitosis o Causes cell wall loosening to allow water uptake and cell expansion o Dwarf plants produce less gibberellin o Flowering plants—gibberellins liberate transcription factors from repressor  proteins  Transcription proteins stimulate cell division/expansion o Removes barriers to gene expression o Promote seed germination and flowering  Ethylene = CH2 o Ripening hormone – also promotes sugar production to increase sweetness &  turns on gene expression for synthesis of carotenoids (fruit color change) o Ethylene gas  leaf drop and fruit ripening o Influences cell specialization, sex determination, flower again, defense against  pathogens, response to mechanical stress o Induces triple response 1. Inhibition of stem/root elongation 2. Swelling/strengthening of stems 3. Formation of stem hook (holds seeds in downward, protective position) **imbalance of auxin  cells on one side of stem elongate faster**  Abscisic acid (ABA) o Produced in shoot system o Slows or stops plant metabolism in poor growth conditions o Induce dormancy – tissues protected within buds and seeds don’t grow until  certain environmental signals occur o Forms tough, protective bud scales around apical meristems during growing  season to prepare for winter o Conserves plant water during drought/salinity/cold o Water­stressed roots produce ABA via terpene pathway—prevents water loss  from leaves by causing stomata to close 13.3 Plants use pigment-containing molecules to sense their light environments  Seeds cannot germinate without light  Successful seed establishment depends on ability of seeds to measure light period Seeds measure light & time periods with light­responsive molecules  Phytochromes perceive light; react to far­red light and 2 pigments that absorb blue &  UV radiation o Cryptochrome o Phototropin o Combo of pigment & protein – light absorption by pigment  change in protein o Control seed and spore germination  “Light sensor” molecules function like light switches  Phytochrome switched off – absorbs red light (Pr) & turns on  Phytochrome switched on – absorbs far­red light (Pfr) & turns off  In regulation of chloroplast position, molecules exert influence in  cytoplasm  Other phytochrome molecules induce chemical changes in nucleus  to turn gene expression on or off  Longer exposure to light  more phytochrome molecules activated  Seeds exposed to red light – activated phytochrome turns on genes to end  dormancy and stimulate germination  Phytochrome in seedless plants influences spore germination  proof of  ancient light­sensing system o Control timing of flowering and dormancy  Flowering corresponds to day length  Short­day plants – flower only if day length < critical period (night  length > than critical period)  Long­day plants – opposite  Day­neutral plants – flower regardless of day length as long as it’s long  enough for plant to grow  Photoperiodism – plants’ response to length of light period  Leaf phytochromes measure length of night  Brief light flash during nighttime  short­day plants don’t flower  During darkness, molecules activated (Pfr)  inactivated (Pr) o Reduces gene expression  Flash of light reconverts Pr to Pfr  Phototropism – plants can sense shading and grow into light  Stems bend toward light  Curvature results from greater amount of cell elongation on the  shaded side of tip (auxin is accumulated there) Chapter Wrap-up Examine and Discuss Self Test  1. What are hormones? List some examples of plant hormones and how they are useful to humans. 2. What is phytochrome and how does it act like an “on/off” switch? It is a light sensor that absorbs red light to turn on gene expression to end dormancy and far red light to turn off. 4. How does light sensing in phototropism differ from light sensing in seed germination? 5. What are short-day, long-day, and day-neutral plants, and how do these plants determine day length? 6. Why do relatively few pathogen attacks actually cause dis- ease? 7. How can plants that have been attacked by herbivores warn neighboring plants to be on guard? Applying Concepts  1. Tomato plants have been genetically engineered so that transcription of one of the genes required to make ethylene has been blocked. What effect would you anticipate this loss of endogenous ethylene to have on the tomato plant? How could this effect be easily reversed? 2. Poinsettias are familiar plants to most people. Sold in late November and December, their verdant foliage and large colored bracts that surround the small flowers brighten the holidays. Yet such plants, maintained as houseplants, rarely bloom a second time. Knowing that poinsettias are short- day plants, why do you think they rarely re-flower and how might you get them to flower again? 3. Many fruits, such as apples, oranges, and grapefruits are sold in grocery stores in perforated bags. What is the purpose of the holes in these bags?


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