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Chp9 growth and development


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2nd year

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Chp9 growth and development

  2. 2. 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
  3. 3. MEASURING GROWTH Increase in fresh weight Increase in dry weight Volume Length Height Surface area
  4. 4. MEASURING GROWTH Definition:  Size increase by cell division and enlargement, including synthesis of new cellular material and organization of subcellular organelles.
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. GENETIC FACTORS AFFECTINGGROWTH 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
  13. 13. GENETIC FACTORS AFFECTINGGROWTH 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
  15. 15. ENVIRONMENTAL FACTORSINFLUENCING 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
  16. 16. ENVIRONMENTAL FACTORSINFLUENCING 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
  17. 17. ENVIRONMENTAL FACTORSINFLUENCING 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
  18. 18. ENVIRONMENTAL FACTORSINFLUENCING 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
  19. 19. ENVIRONMENTAL FACTORSINFLUENCING 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
  20. 20. ENVIRONMENTAL FACTORSINFLUENCING 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
  21. 21. ENVIRONMENTAL FACTORSINFLUENCING 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
  22. 22. ENVIRONMENTAL FACTORSINFLUENCING 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. REPRODUCTIVE GROWTHAND 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
  27. 27. REPRODUCTIVE GROWTHAND DEVELOPMENT Flower induction and initiation  What causes a plant to flower?  Daylength (photoperiod)  Low temperatures (vernalization)  Neither
  28. 28. REPRODUCTIVE GROWTHAND 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
  29. 29. REPRODUCTIVE GROWTHAND 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
  30. 30. REPRODUCTIVE GROWTHAND 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
  31. 31. REPRODUCTIVE GROWTHAND 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
  32. 32. REPRODUCTIVE GROWTHAND 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)
  33. 33. REPRODUCTIVE GROWTHAND 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
  34. 34. REPRODUCTIVE GROWTHAND 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
  35. 35. REPRODUCTIVE GROWTHAND 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
  36. 36. REPRODUCTIVE GROWTHAND DEVELOPMENT Fertilization  Angiosperms (flowering plants)  Termed double fertilization  Gymnosperms (cone-bearing plants)  Staminate, pollen-producing cones  Ovulate cones produce “naked” seed on cone scales
  37. 37. REPRODUCTIVE GROWTHAND 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
  38. 38. REPRODUCTIVE GROWTHAND 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)
  39. 39. 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