RRES_150_Slides_Part_2 - Plant Science (RRES 150) Plant...

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Unformatted text preview: Plant Science (RRES 150) Plant PART II Environment in Horticulture Environment Plant Hormones and Growth Substances Growth Page 30 Hormone - an endogenous or naturallyan occurring compound that is produced or occurring synthesized in one part of the plant and causes a change in physiology, growth or development in another part of the plant; usually present in very small quantities. usually Growth Substance - all naturallyGrowth all occurring or synthetically produced occurring substances that affect the physiology, growth and development of plants. Page 30 Auxin Auxin Natural Synthetic Indolebutric acid (IBA) Naphthaleneacetic acid (NAA) 2,4-dichlorophenoxyacetic 2,4-dichlorophenoxyacetic acid (2, 4-D) acid Indoleacetic acid (IAA) Structure Site of Production Shoot tips Embryos Page 31 Auxin Auxin 1) Tropism - response of plants to environmental or physical stimuli. 2) Apical dominance determined by apical bud, partly due to auxin produced a) phototropism- response response to light b) geotropism - response to gravity c) thigmotropism response to touch Page 31 Auxin (continued) Auxin 3) Fruit set - low 3) concentrations stimulate 4) Fruit or flower thinning - high concentrations cause 5) Herbicides - 2,4-D at high concentrations 6) Adventitious root formation a) stem and leaf cuttings b) tissue culture Page 30 Cytokinin Cytokinin Natural Zeatin Kinetin (not in plants) Synthetic Benzyladenine (BA) Pyranylbenzyladenine (PBA) Structure Site of Production Root tips Embryos Page 31 Cytokinin Cytokinin 1) Leaf aging or abscission 1) may delay 2) Seed germination - may overcome dormancy or stimulate germination 3) Adventitious shoot formation a) leaf and root cuttings b) tissue culture b) Page 30 Gibberellic Acid Gibberellic Natural Over 70 different compounds Over (GA) (GA) Synthetic None Structure Site of Production Shoot tips Root tips Embryos Page 32 Gibberellic Acid (GA) Gibberellic 1) Rosette or dwarf plants - lack of endogenous 1) GA often causes. GA growth retardants - chemicals that block GA synthesis; are used in greenhouse and bedding plant production to produce compact plants. produce 2) Flowering - may cause bolting in biennials 2) Page 32 Gibberelic Acid (GA) continued continued 3) Fruit size - increases size 3) of seedless grapes 4) Bud dormancy - may overcome and substitute for cold treatment 5) Seed germination - may increase or speed up 6) Sex expression - favors staminate flower formation on monoecious plants on Page 30 Ethylene Ethylene Natural Synthetic Etephon Ethrel Both release ethylene inside the Both plant plant Ethylene Structure Site of Production Ripening Fruits Aging Flowers Germinating Seeds Wounded Tissue Ethylene Ethylene 1) Fruit ripening - stimulates in 1) many fruits, ex. banana 2) Flowering - triggers flowering in some bromeliads, ex. pineapple 3) Flower longevity - causes senescence (death) of cut flowers 4) Leaf abscission (leaf drop) causes in some plants 5) Leaf epinasty (curling and contortion of leaves) - causes in some plants 6) Sex expression - favors pistillate flower formation on monoecious plants monoecious Page 32 Page 30 Abscisic Acid Abscisic Natural Synthetic Abscisic Acid (ABA) none Structure Site of Production Plastids, especially Plastids, chloroplasts chloroplasts Page 32 Abscisic Acid (ABA) Abscisic 1. Dormancy – causes bud or seed dormancy causes 2. Leaf abscission – may cause in some plants 3. Stomata – causes stomata to close Page 33 Relationship between temperature, heat, and energy temperature, Temperature Qualitative measure of heat energy Intensity or degree Heat Quantitative measure of heat energy Amount calorie (cal) - amount of heat energy required to raised 1 g of water by 1oC. to C. kilocalorie (kcal) - 1,000 calories British Thermal Unit (BTU) - amount of heat required to raise 1 lb. of water by 1oF. required F. Page 33 Ways to Transfer Heat Energy Ways 1. Conduction - flow of heat energy through a medium from molecule to molecule. 2. Convection - mass movement of heat energy. 3. Radiation - flow of energy as electromagnetic waves, with no transferring medium; when radiation is absorbed it may be converted to heat energy. Page 33 Measures of Heat Energy Measures specific heat - calories needed to raise 1 g of a substance by 1 oC. C. (water = 1.0) heat of fusion - calories needed to change 1 g of a substance from solid to liquid at its melting/freezing point. solid (water = 80 cal/g) heat of vaporization - calories needed to change 1 g of a substance from liquid to gas at its boiling/condensation point. liquid (water = 540 cal/g) Page 35 Water and Heat Energy Water 80cal/g 540cal/g From wikimedia.org Page 35 Practical Application of Heat Energy Practical 1. specific heat stabilizes the temperature of plants stabilizes (plants are 75-95% water) (plants stabilizes the temperature of the environment, stabilizes esp. around large bodies of water used for low intensity heat production if you freeze a 55 gal drum of water: 55 gal x if 8 lb/gal x 454 g/lb x 80 cal/g = 16 million calories or 45,000 BTU released calories causes cooling of plants, animals and the causes environment environment evaporative cooling system, or fan-and-pad evaporative cooling system sprinkler irrigate greenhouse or nursery crops sprinkler in mid afternoon 2. heat of fusion 3. heat of vaporization Page 35 Practical Application of Heat Energy Heat 1. infrared (IR) radiation a form of radiation easily converted to heat energy when absorbed, and vice versa infrared heaters radiational cooling frost protection with fog, smoke and overhead coverings 2. change of state constant temperature when two phases of water are present frost protection with overhead irrigation pressure cooking Page 34 Green House Effect Green Page 35 Global Warming Global http://www.ipcc.ch Page 36 Climate Climate Climate - the average atmospheric conditions over a long period of time. temporary atmospheric conditions. macroclimate - the climate Weather - the current and or weather conditions of a relatively large area, usually 24 to 50 miles. local climate - the climate or weather conditions of a smaller localized area; ex. a valley, stand of trees, open field, sides of a hill, etc. microclimate - the climate or weather conditions of a very small area, ex. inside vs. outside a canopy, upper vs. lower leaf surface, etc. Page 36 Climate Zones Climate Tropical Climatic Zone The area between the 23.5o latitude N and S of equator. Between the Tropic of Cancer and the Tropic of Capricorn. Warm, rarely if ever freezes Temperate Climatic Zone The area between the 23.5o and 66.5o latitude N & S. Between Tropic of Cancer and Arctic Circle, and Tropic of Capricorn and Antarctic Circle. Has hot and cold seasons sub-tropical - often used to describe the southern most area of the Temperate Climatic Zone (ex. South Florida and Rio Grande Valley), but it is not an official climatic zone Arctic Climatic Zone The area between the 66.5o N latitude and the N. Pole and the 66.5o S latitude and the S. Pole. North of Arctic Circle, and south of Antarctic circle. Always cold and frozen Arctic Page 37 Factors that affect temperature Factors Latitude - average temperature decreases north and south from equator sun's rays spread over greater area sun's rays pass obliquely through thicker layer of sun's atmosphere Temperate Time of Year or Seasonal Variation temperature fluctuates most in the Temperate Zone Time of Day minimum average temperature: just before sunrise minimum maximum average temperature: mid-afternoon maximum Tropical Page 37 Factors that affect temperature Factors Elevation or Altitude small scale - hot air rises, cold air small sinks into low areas. large scale - the temperature large decreases 0.6oC/100 m or 1oF/330 ft decreases F/330 increase in altitude. increase Slopes - warmest to coldest slopes of a hill or side of a building: south > west > east > north Water Bodies - stabilize temperature; warmer in winter, cooler in summer Soils dark soils warm faster than light soils in spring dry soils warm faster than moist soils in spring Page 38 Seasons Seasons The earth's axis is tilted 23 1/2 degrees relative to the axis of the sun. As the earth revolves around the sun, the axis remains pointed in the same direction in space, changing the day length Watch Animation http://www.rkm.com.au/ANIMATIONS/animation-seasons.html Page 39 Temperature effects on growth and survival Temperature Cardinal Temperature - the temperature range in which plants grow and survive. Minimum Cardinal Temperature a) growth: 40-50oF (5-6oC) for most species b) survival 1. tender or chilling sensitive: 32 to 45oF (0 to 7oC) 2. semi-hardy plants: 15 to 29oF (-9 to -2oC) 3. hardy plants: less than 0oF (-18oC) Optimum Temperature a) cool-season plants: grow best at 65-75oF (18-24oC) b) warm season plants: grow best at 78-90oF (24-32oC) 1. in southern U.S.: grow as fall-winter crops. 2. in northern U.S.: grow in late spring, summer, early fall 1. in southern U.S.: grow in late spring and summer, early fall 2. in northern U.S.: grow in summer, but for some warm season crops the growing season may be too short to get good yield. Maximum Cardinal Temperature a) growth: 90-96oF (32-36oC), most species o o Page 40 High Temperature Damage High Dies quickly Dies Denatures proteins (unfolding of Denatures proteins) at 130oF proteins) Desiccation causes excessive drying-out causes Sun scald or scorch desiccation followed by death of desiccation tissue Respiration exceeds photosynthesis depletes stored food depletes Dies slowly or just poor growth Page 40 Methods to decrease high temperatures temperatures 1. Soil temperature 1. mulch - insulates and blocks out mulch light light 2. Air temperature 1. Decrease light intensity (decrease both visible and infrared if possible) 1. lath covering over nursery crops 2. shade cloth or saran over nursery crops or greenhouses 3. shading compound or white wash painted on greenhouse roof 4. colored solution flowing through a doublelayered greenhouse roof (primarily decreases IR) Page 40 Methods to decrease high temperatures temperatures 1. Evaporative cooling (relies on heat of vaporization) 1. spray foliage and physical structures during midafternoon 2. fine mist or fog injected into a greenhouse 3. fan-and-pad cooling system in a greenhouse Page 41 Cold Temperature Damage Cold Chilling Injury damage or death due to cold, yet above freezing temperatures (32 to 45 oF). Freeze Injury - damage or death due to temperatures below freezing (below about 28 oF). Page 41 Types of Freezes Types 1) Radiational Freeze or Frost - temperature drops due to radiational cooling which results in a temperature inversion; occurs on calm, clear nights. • radiational cooling - loss of heat by long wavelength infrared (IR) radiation. • temperature inversion - a warm air mass above a cold air mass. • dew point - the temperature at which air reaches 100% relative humidity. 2) Advective Freeze - temperature drops due to the invasion of a cold air mass or convection current. Page 42 Development of Radiational Freeze Freeze Night 2. No wind 3. No cloud No cover cover All conditions have to occur together 1. Conditions for Conditions Occurrence Occurrence Page 41 Types of Radiational Freezes Freezes a) white frost - occurs when the temperature drops below both the current dew point (dew forms) and below freezing (dew freezes). b) black frost - occurs when the temperature drops below freezing, but remains above the current dew point. Page 43 Injury from Chilling Temperature (slow death) (slow 1. Increased protein and enzyme Increased breakdown breakdown 2. Increased membrane leakiness a) Membranes lose selective permeability b) Leaves often appear deeper green and Leaves slightly water logged slightly Examples of sensitive plants Tropical plants Tropical fruits Summer annuals and bedding plants Chilling sensitive vegetables Page 43 Injury from Freezing Temperature (slow or fast death) (slow 1. individual cells individual a) Very rapid temperature drop Direct cellular damage – damage to Direct Ice forms in cytoplasm and ruptures cell Seldom occurs, but always fatal Ice forms in cell wall and cytoplasm Ice dehydrates dehydrates Occurs most, not fatal to hardy or cold Occurs acclimated plants acclimated Cold soil impedes water uptake Dry winds increase evaporation Soil freezes and expands, thus heaving the Soil plant out of the soil plant b) Moderate temperature drop 2. 3. Desiccation – Excessive drying out Frost heaving Injury from Freezing Temperature (slow or fast death) Continued (slow 1. Bark splitting Cambium under bark freezes, Cambium expands and splits the bark expands Page 43 2. Physical or mechanical Physical breakage (ice damage) breakage Weight of ice on the plants 3. Sun scald or southwest injury Excessive desiccation on the Excessive area of the tree receiving brightest sun light brightest Page 43 Sensitivity to freezing injury Sensitivity Sensitive Young Tissue Growing Tissue Flower Buds Roots Resistant Mature Tissue Dormant Tissue Vegetative Buds Shoots Page 44 Prevention of Radiational Freeze or Frost Radiational 1. Decrease radiational cooling a) b) c) d) e) Hot caps or plastic tents Mulches Foams Fog or Water Vapor Smoke Prevention of Radiational Freeze or Frost Radiational (continued) 1. Increase air temperature a) Eliminate temperature inversion 1) Wind machines 2) Helicopters Page 44 b) Irrigation a) Water is warmer and stabilizes Water temperature temperature b) Temperature stays at 32ºF when when liquid water is present liquid c) Oil burners and smudge pots Page 44 Prevention of Advective Freeze Damage Advective 1. Select frost adapted plants 2. Some of the radiational freeze methods a) b) c) Hot caps or plastic tents Mulches Foams Avoid north side of hills, buildings etc. Avoid low areas, valleys etc. Avoids damage to new spring growth and flower buds from late Avoids spring frost spring Normal preparation of the plant for winter (dormancy) 3. Site selection 4. Delay development in spring 5. Harden-off or cold acclimation in fall Page 44 Cold Acclimation Cold Naturally triggered by: Naturally a) short days b) cool temperatures c) cold temperatures Allow to occur naturally by observing the following: observing 1) Do not encourage growth: a) decrease fertilization b) decrease watering c) avoid pruning 2) Avoid stress a) insect, disease or physical damage b) poor nutrition and nutrient deficiencies c) too heavy fruit load Page 45 Two Types of Dormancy Two Dormancy- a state of inactive growth. Purpose - to survive adverse conditions Quiescence Dormancy imposed by Triggers external or environmental conditions a) b) Unfavorable environmental conditions External factor, such as hard seed coat Causes Unfavorable environment; too dry, cold, hot, etc. Remove unfavorable environment How to overcome Page 45 Two Types of Dormancy Two Rest or Rest Physiological Dormancy Physiological Dormancy imposed internal or physiological conditions by Triggers a) b) Short days (SD) Decreasing temperatures Low level of growth promotors (e.g. auxin or gibberellic acid) High level of growth inhibitors (e.g. ABA) Causes a) b) How to overcome Give period of cold between 32-45 ºF (0-7 ºC), which satisfies the chilling requirement. Plants and Organs that Exhibit Rest that Flower buds – usually shorter chilling requirement Vegetative buds – usually longer chilling requirement Page 46 Common among temperate perennial plants Vegetative and flower bud dormancy Flowering bulb dormancy Cold storage or bulb chilling usually 6-12 weeks at 35-45 ºC (0-7 ºC) in a cooler or refrigerator Seed Rest or Embryo Rest Cold is required for seeds of some temperate trees and shrubs to germinate Stratification - moist, cold (32-45 ºF, 0-7 ºC) storage for 6-12 weeks required to overcome embryo rest (physiological dormancy) Page 48 From: G.R. McEachern. 1990. Growing Fruits, Berries and Nuts: Southwest-Southeast, Gulf Publishing Co., Houston, TX Chilling requirement: the number of hours of cold between 32-45 ºF (0-7 ºC) required to satisfy rest. Chilling Requirements for Temperate Fruit Trees Temperate Crop Peach Page 47 Cultivar Red Haven June Gold EarliGrande Montmorency Ozark Primer Methley Golden Delicious Granny Smith Maxine Orient Stuart Desirable American cultivars French cultivars Most cultivars Chilling Hour Requirement 950 650 250 1000 750 600 1000 600 850 650 500 400 100 none none Cherry Plum Apple Pear Pecan Grape Citrus The chilling hour requirement of fruit trees must be matched to the chilling hour zone where the tree is to be grown. Your local county agent should be able to give you a list of cultivars that are adapted to your chilling hour zone. Reputable nurseries should only sell fruit tree cultivars adapted to your region. Effect of Chilling Hour Effect Peach Variety Earligrande Chilling Hour Requirement 250 Brownsville 200 hour zone normal flowering College Station 600 hour zone flowers early in spring, likely killed by late frost Page 47 Table shows what happens if you plant peach cultivars with different chilling hour requirements in various chilling hour zones across Texas. Wichita Falls 1000 hour zone flowers very early in spring, definitely killed by frost flowers early in spring, likely killed by late frost normal flowering June Gold 650 flowers late if at normal flowering all; would still grow vegetatively flowers very late if at all; would still grow vegetatively flowers late if at all; would still grow vegetatively Red Haven 950 Page 49 Vernalization and Biennials Vernalization Biennial: Plants that have a 2 year life cycle Biennial life cycle: 1st year – Grow vegetatively as rosettes or bulbs in late summer-fall Winter – Cold of winter triggers flower inception (Vernalization) 2nd year – in spring flower forms and develops, called bolting Page 49 Vernalization and Biennials (continued) (continued) Definitions: Vernalization - a cold treatment (32-45 oF for 4-12 weeks) required to trigger or initiate flower formation in biennials. Bolting - flower formation and seed stalk elongation in biennials De-Vernalization- exposure (1 day to 1 week) to high temperatures (90-95 oF) immediately after vernalization, which erases the vernalization treatment. Site of Perception - growing point (apex) of stems. Page 49 Vernilazation and Biennials (continued) Vernilazation Growth Habits: Rosettes – radish, carrot, turnip, mustard, kale, bluebonnet, Indian paint brush Heads - cabbage Bulbs- onion Page 50 Light Light ENERGY TRANSFER - light is one of the ways in which energy is transferred. 1. conduction - molecule to molecule. 2. convection - mass movement. 3. radiation- radiant energy transferred as electromagnetic waves. Page 50 Properties of Light Properties light - light is the layman's term for visible radiant energy in the 400 to 700 nm wavelength region of the spectrum. In other words, it is the form of radiant energy (i.e. radiation) that animals can see. It is also the wavelengths of radiant energy that plants use in photosynthesis and for most other reactions that require light. FOUR PROPERTIES OF LIGHT 1. quantity - the intensity or amount of light. 2. quality - the wavelength or color of light. 3. duration - determines the total amount of light energy received. total amount of light energy = quantity x # hours of light. 4. Photoperiod - the day length, or length of light in a 24 hour cycle, regardless of quantity. Page 50 Properties of Light (continued) Properties Light can be affected as follows 1. Absorbed - when radiant energy (such as light) is absorbed it is converted primarily to heat energy. 2. Re-radiation - heat energy is converted to radiant energy as long wavelengths in the infrared (IR) region of the spectrum. 3. Transmitted - when radiant energy (such as light) passes through an object unaffected, such as glass. 4. Reflected or scattered - when radiant energy (such as light) is "bounced off" an object, such as a solid colored surface. The color of an object is the color (as determined by wavelength) of light that is transmitted or reflected. In other words, your eyes see the color that is not absorbed. Page 51 Measurement of Light Intensity Measurement 1. photometer or common light meter (cheapest) - measures amount of luminance (500-600 nm). Expressed as: a) foot-candle (ft-c) - 1 lumen per square foot b) lux - 1 lumen per square meter 1 foot-candle = 10.76 lux Page 51 Measurement of Light Intensity Measurement 1. quantum sensor - measures actual light intensity or light energy in the 400-700 nm wavelength band. photosynthetically active radiation (PAR) - light intensity in the 400-700 nm wavelength band that is used by plants in photosynthesis. Expressed as: microEinstein per second per square meter - μEs-1m-2 (400700 nm) Watts per square meter - Wm-2(400-700 nm) Page 51 Measurement of Light Intensity (continued) Measurement Page 51 Measurement of Light Intensity Measurement 1. radiometer - measures radiant energy received at all wavelengths, i.e. total solar radiation (350-800 nm). 2. spectral radiometer measures the intensity at each wavelength (i.e. color spectrum from a light). Effect of light quantity in plants in Page 52 1. phototropism - response of plants to light a)plants bend towards areas of higher light intensity. 2. photosynthesis a)light reaction - increases with increasing light intensity b)stomata - C3 and C4 plants: open in light; close in dark c)stomata - CAM plants: open in dark; close in light Effect of light quantity in plants in 1. temperature high light intensity increases temperature due to: a) absorption of radiation, especially IR; greater with darker colors b) greenhouse effect 2. transpiration - greater in high light intensity due to heat buildup, but transpiration may decrease if it gets too bright then too hot, which will cause the stomata to close. Page 52 Page 52 Effect of light quantity in plants (continued) Effect Sun Grown Maple Leaf 1. Sun versus shade plants a) Leaf structure (dicot leaves) Sun Grown Leaf Thicker due to thicker palisade mesophyl layer Thinner, due to thinner palisade layer Higher proportion spongy mesophyl Larger size (surface area) Softer and more pliable Shade grown Leaf Shade Grown Maple Leaf b)Optimum light intensity Sun plants have a high optimum light intensity Shade plants have a low optimum light intensity Images from http://www.lima.ohio-state.edu/biology/archive/leaves.html Effect of light quantity in plants (continued) in 1. Photooxidation 2. Etiolation Page 52 destruction of chlorophyl by high light intensity elongated, pale green to yellowish growth due to low light intensity lack of color development due to exclusion of light used on cauliflower, asparagus, and celery conditioning of plants to low light intensity interior environments 3. Blanching 4. Light acclimatization Indoor Performance of shade versus sun foliage plants versus Plant Name 15-25 ft-c 12 12 30 12 12 12 Page 53 Number of Months of Attractive Live At Various Indoor Light Intensities 25-50 ft-c 36 24 - 50-75 ft-c 36 36 - 75-100 ft-c 36 38 - Shade Plants (lowest light tolerant) Cast Iron Plant Aucuba Janet Craig Dracaena Sander's Dracaena Heart-Leaf Philodendron Mother-in-Law's Tongue Shade Plants (moderate light tolerant) Norfolk Island Pine Schefflera, Umbrella Plant Anthurium Spider Plant Boston Fern Aluminum Plant 36 30 12 30 12 12 36 36 38 38 36 - Indoor Performance of shade versus sun foliage plants (continued) foliage Plant Name Sun Plants Weeping Fig Rubber Plant Grape Ivy English Ivy - Page 53 Number of Months of Attractive Live At Various Indoor Light Intensities 15-25 ft-c 25-50 ft-c 50-75 ft-c 75-100 ft-c 12 12 12 12 from: G. Thames and M.R. Harrison. 1966. Foliage Plants for Interiors. Bulletin 327-A, Rutgers University, New Brunswick, NJ) Page 54 Effect of light intensity on photosynthesis/respiration relationship Effect of light intensity on photosynthesis/respiration relationship photosynthesis/respiration sun versus shade plants sun Page 54 Pages 55 &56 Methods of light acclimatization 1. Grow plants under reduced light intensity for entire Grow production time (most commonly used method). production Greenhouse covered with shade cloth to yield the Greenhouse required light intensity required Production time longer Plants taller with deeper green leaves Plants can be used immediately 2. Give final period of greatly reduced light intensity Give after growth under high light intensity after Plants can not be used indoors immediately after growth Plants in high light intensity in a) b) c) Growth stops Leaves turn yellow, especially older leaves Leaves fall off, especially the older leaves Page 55 Reduced light intensity requirements Common Name Zebra Plant Chinese Evergreen Pilea Peacock Plant Dumbcane Asparagus Ferns Norfolk Island Pine Rubber Plant Croton Scientific Name Aphelandra squarrosa Aglaonema spp. Pilea spp. Calathea spp. Dieffenbachia spp. Asparagus spp. Araucaria heterophylla Ficus elastica Codiaeum variegatum Suggested Light Intensity (ft-c) 1000-2000 2000-2500 2000-3500 3000-3500 3000-4500 3500-4500 5000-6000 5000-8000 7000-8000 % Shade (in summer) 80-90% 80% 73-80% 73% 63-73% 63% 55% 30-55% 30% Page 56 Acclimatization Acclimatization Recommendation: Grow plants at high light intensities. Acclimatize plants for 4-6 weeks at very low light intensities (about 150-500 ft-c) in a heavily shaded greenhouse or lighted warehouse. From: W.C. Fonteno and E.L. McWilliams J. Amer. Soc. Hort. Sci. 103(1):52-56, 1976) Page 57 Effect of Light Quality on Plants Effect 1. Photosynthesis a) Chlorophyl absorbes predominantly blue and Chlorophyl orange-red light orange-red b) Green-yellow are transmitted and reflected 2. Growth responses – due to effect on photosynthesis Growth a) Colored coverings 1. 2. 3. 4. Plant canopy – shade rich in green-yellow light, poor in blue and orange-red light Fiberglass Tinted/shaded glass Shade cloth or saran Tungsten – rich in red and far red Fluorescent – rich in blue and yellow-orange HID - varies b) Artificial light sources 1. 2. 3. Page 57 1. Pigments Effect of Light Quality on Plants (continued) (continued) a) Anthocyanins Anthocyanins blue, red and purple in color orange and yellow in color absorb blue and green (450-500 absorb nm) light nm) can pass energy to chlorophyl to can assist in photosynthesis assist Absorbs red (660 nm) Absorbs and far red (730 nm) light and Involved in photomorphogenic Involved and photoperiodic responses (day length) b) Carotenoids c) Phytochrome Page 57 Effect of Light Quality on Plants (continued) (continued) 1. Seed germination Some seeds only germinate Some when exposed to sun light and need to be sown on the soil surface (not buried) surface a) Sun light and any white or red Sun light causes germination light Pfr form of phytochrome present b) Far red light inhibits Far germination germination Pr form of phytochrome present Page 58 Response of plants to photoperiod Response Plant Types: 1. Short-day plant (SDP) Responds when photo period is shorter than Responds shorter a critical level critical Example retracts resources from leaves in Example the fall when day length decreases below critical value critical Responds when photo period is longer than Responds longer a critical level critical Example starts flowering (bolting) in the Example summer when day length exceeds critical value Does not respond to photo period 2. Long-day plant (LDP) 3. 3. Day-neutral plant (DNP) Page 58 Photo Period Photo civil twilight - reflected sky light that occurs approximately 1/2 hour before sunrise and 1/2 hour after sunset. Plants can detect civil twilight, so it must be taken into account when determining the photoperiod that plants perceive. Plants cannot detect moonlight, so it does not effect the photoperiod plants perceive. photoperiod - the day length a plant perceives, which will be the absolute day length (time from sunrise to sunset) plus 1 hour of civil twilight. critical photoperiod - the photoperiod (absolute day length + civil twilight) above or below which the photoperiodic response is turned-on or turned-off. Each species has its own unique critical photoperiod that it "looks" for. Page 58 Examples of Plants Based on Response to Photoperiod Response Flowering Short-Day Plants chrysanthemum poinsettia kalanchoe strawberry soybean Jerusalem artichoke tuberous begonia none none maple sumac dogwood birch dogwood birch - Long-Day Plants sedum tuberous begonia carnation radish spinach onion bryophyllum spider plant strawberry none none none most plants Day-Neutral Plants bean tomato squash rose corn tulip crocus piggy-back plant grasses coleus foliage plants many temperate trees many temperate trees - Bulbs and Tubers Plantlets Runners Color Development Dormancy Cold Acclimatization Elongation of Stems Mechanisms of Photoperiodic Responses Mechanisms Light Perception, Timing and Floral Induction in Light Short-Day Plants Short-Day Page 59 All the critical events happen at night, therefore plants are not photoperiodic but rather are nyctiperiodic. Short-day plants really are long-night plants Page 59 Mechanisms of Photoperiodic Responses Mechanisms Response of photoperiodic plants to different photo periods It is the trend in response to photoperiod that is important, not the absolute day length. Photoperiod SDP ( ex. Chrysanthemum) 14.5 hr critical photoperiod flowers flowers flowers no flowers no flowers no flowers LDP ( ex. Henbane) 11 hr critical photoperiod no flowers no flowers flowers flowers flowers flowers 4 hour 8 hour 12 hour 16 hour 20 hour 24 hour Day Neutral Flowers bloom at any day length Page 59 Mechanisms of Photoperiodic Responses Mechanisms Manipulating flowering in photoperiodic plants Horticulturist manipulate the light and dark periods to which plants are exposed in order to trigger photoperiodic plants to flower during any season of the year. That is why you can purchase a chrysanthemum year round. ...
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This note was uploaded on 05/13/2011 for the course RRES 150 taught by Professor N/a during the Spring '11 term at University of Louisiana at Lafayette.

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