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  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. MEASURING GROWTH • Increase in fresh weight • Increase in dry weight • Volume • Length • Height • Surface area

  4. MEASURING GROWTH • Definition: • Size increase by cell division and enlargement, including synthesis of new cellular material and organization of subcellular organelles.

  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. 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. 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. 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. 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. 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. 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. 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

  13. 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


  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  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. 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. 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. 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

  27. REPRODUCTIVE GROWTH AND DEVELOPMENT • Flower induction and initiation • What causes a plant to flower? • Daylength (photoperiod) • Low temperatures (vernalization) • Neither

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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)

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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)

  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