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Light and Temperature Interaction Modified by Georgia Agricultural Education Curriculum Office June, 2002 August 2008 Fall Leaf Color • cool temps - very bright days August 2008 Orange • yellow, reds, purples and browns • chlorophyll cells die as temperatures get cooler August 2008 Yellow • carotenoids • after chlorophyll dies you see the other pigments that are always present August 2008 Red-Purple • anthocyanins • not always present • synthesized in cooler temps • made from sugar molecules August 2008 Brown • tannins • mask or show up more once chlorophyll dies • produced in the leaves August 2008 Leaf Fall • need an abscission layer • leaf can no longer translocate carbohydrates out of the leaf August 2008 Bright Days • lots of carbohydrates in the leaf • anthocyanins get brighter color August 2008 The Key…… • cool, short days August 2008 Greenhouse Effect • short, high energy wave lengths of light from sun enters house • absorbed by structures and plants August 2008 Greenhouse Effect • plants re-radiate green light in longer waves • long waves do not have as much energy as the short waves August 2008 Greenhouse Effect • longer waves do not have enough energy to escape from the house • result is heat August 2008 Greenhouse Effect • this is how the earth is heated • long waves cannot escape through the clouds • cloudy nights are warmer August 2008 Light • energy - electromagnetic radiation • wavelengths - distance from peak to peak • measured in nanometers “NM” August 2008 Far Red • color plants use August 2008 Infra Red • heat energy August 2008 Visible light • light quality - color • quantity - intensity, how bright • duration - photoperiod August 2008 Quality • blue - 400-510 NM • cell elongation • photosynthesis - chlorophyll absorbs red and blue light August 2008 Quality • phototropism - plant tends to grow or bend toward a light source August 2008 Red • photosynthesis • stimulates branching • encourage growth of auxiliary buds August 2008 Red • phytochrome - light absorbing pigment • seed germination in photoblastic seeds August 2008 Red • flowering responses • photoperiod August 2008 Far Red • filters through leaf • inhibits branching phytochrome reactions - inhibits germination of photoblastic seeds August 2008 Far red • promotes stem elongation August 2008 Yellow - Green • does not effect plants August 2008 Intensity • measured in foot candles • amount per unit area on plant August 2008 Plants • shade loving • too much sun - leaf burn • dehydrate • kill chlorophyll August 2008 Plants • sun loving • low light, pale color • new leaves are small • lack vigor August 2008 Plants • don’t flower properly if at all August 2008 Light • Light Compensation Point ”LCP” • light intensity where rate of photosynthesis = the rate of respiration August 2008 LCP • Lowest intensity you can grow a plat at • If a plant is grown below this level, respiration will be greater than photosynthesis August 2008 LCP • plant will die • for a plant to grow photosynthesis must be greater than respiration August 2008 Acclimitization • preparing plant for lower light intensity conditions • expose to lower light intensity August 2008 Artificial Lights • Incandescent • far red, red - elongation • low blue • 80% of emitted radiation is heat August 2008 Incandescent • 20% visible light • 12% utilized by plant August 2008 Flourescent • red, blue • 36% heat energy • 22% light used by plant • spectral flexibility August 2008 Flourescent • can change the quality of the light by changing the coating on inside of bulbs • Cool White - Ca Halophosphate August 2008 “Gro-Lux” • coated with Mg Fluorogerminate • not as long life as cool white, 30X more expensive August 2008 Metal Halide • increase light intensity August 2008 Low Pressure Sodium • yellow glow • energy efficient • yellow - orange light August 2008 High Pressure Sodium • red, blue light • energy efficient August 2008 Photoperiod • length or duration of the light period • biological measurement of relative length of light and dark periods August 2008 Photoperiod • effects • flowering • leaf abscission • dormancy - acclimate for winter August 2008 Effects….. • Sex expression • runner formation • tuber formation • bulb formation August 2008 Short Day Plants • flower when day length is shorter • the dark period is critical • it’s dark longer than it is light August 2008 Short Day Plants • examples • Chrysanthemum • Christmas Cactus • Poinsettia August 2008 Long Day Plants • flower when days are long and nights are short • example: lettuce, radish, petunias August 2008 Facilitative Long Day • flower any period • if long day - flowering is enhanced • examples - tomato, begonia August 2008 Day Neutral • flower under long or short day lengths • example: African Violet August 2008 Poinsettias • use night interrupted lighting • turn on artificial lights from 10 p.m. to 2 a.m. • splits up the dark period August 2008 Poinsettias • cyclic lighting from 10 p.m. to 2 a.m. • lights on for 6 minutes and off for 24 minutes August 2008