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chp9-GROWTHANDDEVELOPMENT

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Information about chp9-GROWTHANDDEVELOPMENT
Science-Technology

Published on December 18, 2008

Author: aSGuest7131

Source: authorstream.com

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GROWTH AND DEVELOPMENT : GROWTH AND DEVELOPMENT VEGETATIVE GROWTH AND DEVELOPMENT : VEGETATIVE GROWTH AND DEVELOPMENT Shoot and Root Systems Crop plants must yield for profit Root functions Anchor Absorb Conduct Store As the shoot system enlarges, the root system must also increase to meet demands of leaves/stems MEASURING GROWTH : MEASURING GROWTH Increase in fresh weight Increase in dry weight Volume Length Height Surface area MEASURING GROWTH : MEASURING GROWTH Definition: Size increase by cell division and enlargement, including synthesis of new cellular material and organization of subcellular organelles. MEASURING GROWTH : MEASURING GROWTH Classifying shoot growth Determinate – flower buds initiate terminally; shoot elongation stops; e.g. bush snap beans Indeterminate – flower buds born laterally; shoot terminals remain vegetative; e.g. pole beans SHOOT GROWTH PATTERNS : SHOOT GROWTH PATTERNS Annuals Herbaceous (nonwoody) plants Complete life cycle in one growing season See general growth curve; fig. 9-1 Note times of flower initiation See life cycle of angiosperm annual; fig. 9-3 Note events over 120-day period SHOOT GROWTH PATTERNS : SHOOT GROWTH PATTERNS Biennials Herbaceous plants Require two growing seasons to complete their life cycle (not necessarily two full years) Stem growth limited during first growing season; see fig. 9-4; Note vegetative growth vs. flowering e.g. celery, beets, cabbage, Brussels sprouts SHOOT GROWTH PATTERNS : SHOOT GROWTH PATTERNS Perennials Either herbaceous or woody Herbaceous roots live indefinitely (shoots can) Shoot growth resumes in spring from adventitious buds in crown Many grown as annuals Woody roots and shoots live indefinitely Growth varies with annual environment and zone Pronounced diurnal variation in shoot growth; night greater ROOT GROWTH PATTERNS : ROOT GROWTH PATTERNS Variation in pattern with species and season Growth peaks in spring, late summer/early fall Spring growth from previous year’s foods Fall growth from summer’s accumulated foods Some species roots grow during winter Some species have some roots ‘resting’ while, in the same plant, others are growing HOW PLANTS GROW : HOW PLANTS GROW Meristems Dicots Apical meristems – vegetative buds shoot tips axils of leaves Cells divide/redivide by mitosis/cytokinesis Cell division/elongation causes shoot growth Similar meristematic cells at root tips HOW PLANTS GROW : HOW PLANTS GROW Meristems (cont) Secondary growth in woody perennials Increase in diameter due to meristematic regions vascular cambium xylem to inside, phloem to outside cork cambium external to vascular cambium produces cork in the bark layer GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT : GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT DNA directs growth and differentiation Enzymes catalyze biochemical reactions Structural genes Genes involved in protein synthesis Operator genes Regulate structural genes Regulatory genes Regulate operator genes GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT : GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT What signals trigger these genes? Believed to include: Growth regulators Inorganic ions Coenzymes Environmental factors; e.g. temperature, light Therefore . . . Genetics directs the final form and size of the plant as altered by the environment ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light Temperature Water Gases ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light Sun’s radiation not all reaches earth; atmosphere absorbs much visible (and some invisible) rays pass, warming surface reradiation warms atmosphere Intensity high in deserts; no clouds, dry air low in cloudy, humid regions earth tilted on axis; rays strike more directly in summer day length varies during year due to tilt ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light (cont) narrow band affects plant photoreaction processes PAR (Photosynthetically Active Radiation) 400-700nm stomates regulated by red (660nm), blue (440nm) photomorphogenesis – shape determined by light controlled by pigment phytochrome phytochrome absorbs red (660nm) and far-red (730nm) but not at same time pigment changes form as it absorbs each wavelength ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light (cont) importance of phytochrome in plant responses plants detect ratio of red:far-red light red light – full sun yields sturdy, branched, compact, dark green plants far-red light – crowded, shaded fields/greenhouses plants tall, spindly, weak, few branches; leaves light green ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light (cont) Phototropism – movement toward light hormone auxin accumulates on shaded side cell growth from auxin effect bends plant blue light most active in process pigment uncertain ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light (cont) Photoperiodism – response to varying length of light and dark shorter days (longer nights) onset of dormancy fall leaf color flower initiation in strawberry, poinsettia, chrysanthemum tubers/tuberous roots begin to form longer days (shorter nights) bulbs of onion begin to form flower initiation in spinach, sugar beets, winter barley ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Temperature correlates with seasonal variation of light intensity temperate-region growth between 39°F and 122°F high light intensity creates heat; sunburned low temp injury associated with frosts; heat loss by radiation contributes opaque cover reduces radiation heat loss burning smudge pots radiate heat to citrus trees wind machines circulate warm air from temperature inversions ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Water most growing plants contain about 90% water amount needed for growth varies with plant and light intensity transpiration drives water uptake from soil water pulled through xylem exits via stomates evapotranspiration - total loss of water from soil loss from soil evaporation and plant transpiration ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH : ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Gases Nitrogen is most abundant Oxygen and carbon dioxide are most important plants use CO2 for photosynthesis; give off O2 plants use O2 for respiration; give off CO2 stomatal opening and closing related to CO2 levels? oxygen for respiration limited in waterlogged soils increased CO2 levels in atmosphere associated with global warming additional pollutants harm plants PHASE CHANGE: JUVENILITY, MATURATION, SENESCENCE : PHASE CHANGE: JUVENILITY, MATURATION, SENESCENCE Phasic development embryonic growth juvenility transition stage maturity senescence death During maturation, seedlings of many woody perennials differ strikingly in appearance at various stages of development PHASE CHANGE: JUVENILITY, MATURATION, SENESCENCE : PHASE CHANGE: JUVENILITY, MATURATION, SENESCENCE Juvenility terminated by flowering and fruiting may be extensive in certain forest species Maturity loss or reduction in ability of cuttings to form adventitious roots Physiologically related lower part of plant may be oldest chronologically, yet be youngest physiologically (e.g. some woody plants) top part of plant may be youngest in days, yet develop into the part that matures and bears flowers and fruit AGING AND SENESCENCE : AGING AND SENESCENCE Life spans among plants differ greatly range from few months to thousands of years e.g. bristlecone pine (over 4000 years old) e.g. California redwoods (over 3000 years old) clones should be able to exist indefinately Senescence a physiological aging process in which tissues in an organism deteriorate and finally die considered to be terminal, irreversible can be postponed by removing flowers before seeds start to form REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Phases Flower induction and initiation Flower differentiation and development Pollination Fertilization Fruit set and seed formation Growth and maturation of fruit and seed Fruit senescence REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Flower induction and initiation What causes a plant to flower? Daylength (photoperiod) Low temperatures (vernalization) Neither REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Photoperiodism (see table 9-5) Short-day plants (long-night; need darkness) Long-day plants (need sufficient light) Day-neutral plants (flowering unaffected by period) Change from vegetative to reproductive Manipulations enable year-round production Market may dictate; consumer’s expectations associated with seasons, e.g. poinsettias at Christmas REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Photoperiodism (cont) Stimulus transported from leaves to meristems Cocklebur Leaf removal – failed to flower Isolated leaf, dark exposure – flowering initiated Believed to be hormone related Interruption of night with light affects flowering Cocklebur Red light, 660 nm, inhibits Far-red, 730 nm, restores Discovery of Phytochrome REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Low temperature induction Vernalization “making ready for spring” Any temperature treatment that induces or promotes flowering First observed in winter wheat; many biennials Temperature and exposure varies among species Note difference/relationship to dormancy Many plants do not respond to changed daylength or low temperature; agricultural REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Flower development Stimulus from leaves to apical meristem changes vegetative to flowering Some SDPs require only limited stimulus to induce flowering; e.g. cocklebur – one day (night) Once changed the process is not reversible Environmental conditions must be favorable for full flower development REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Pollination Transfer of pollen from anther to stigma May be: Same flower (self-pollination) Different flowers, but same plant (self-pollination) Different flowers/plants, same cultivar (self-pollination) Different flowers, different cultivars (cross-pollination) REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Self-fertile plant produces fruit and seed with its own pollen Self-sterile plant requires pollen from another cultivar to set fruit and seed Often due to incompatibility; pollen will not grow through style to embryo sac Sometimes cross-pollination incompatibility REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Pollen transferred by: Insects; chiefly honeybees Bright flowers Attractive nectar Wind Important for plants with inconspicuous flowers e.g. grasses, cereal grain crops, forest tree species, some fruit and nut crops Other minor agents – water, snails, slugs, birds, bats REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT What if pollination and fertilization fail to occur? Fruit and seed don’t develop Exception: Parthenocarpy Formation of fruit without pollination/fertilization Parthenocarpic fruit are seedless e.g. ‘Washington Navel’ orange, many fig cultivars Note: not all seedless fruits are parthenocarpic Certain seedless grapes – fruit forms but embryo aborts REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Fertilization Angiosperms (flowering plants) Termed double fertilization Gymnosperms (cone-bearing plants) Staminate, pollen-producing cones Ovulate cones produce “naked” seed on cone scales REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Fruit setting Accessory tissues often involved e.g. enlarged, fleshy receptacle of apple and pear True fruit is enlarged ovary Not all flowers develop into fruit Certain plant hormones involved Optimum level of fruit setting Remove excess by hand, machine, or chemical Some species self-thinning; Washington Navel Orange Temperature strongly influences fruit set REPRODUCTIVE GROWTH AND DEVELOPMENT : REPRODUCTIVE GROWTH AND DEVELOPMENT Fruit growth and development After set, true fruit and associated tissues begin to grow Food moves from other plant parts into fruit tissue Hormones from seeds and fruit affect growth Auxin relation in strawberry fruits Gibberellins in grape (fig. 9-21, 9-22) Patterns of growth vary with fruits (fig. 9-16, 9-17) PLANT GROWTH REGULATORS : PLANT GROWTH REGULATORS Plant hormones are natural Plant growth regulators include: Plant hormones (natural) Plant hormones (synthetic) Non-nutrient chemicals Five groups of natural plant hormones: Auxins, Gibberellins, Cytokinins, Ethylene, and Abscisic acid

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