GROWTH AND DEVELOPMENT

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GROWTH AND DEVELOPMENT
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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

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MEASURING GROWTH

• Increase in fresh weight
• Increase in dry weight
• Volume
• Length
• Height
• Surface area

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MEASURING GROWTH

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

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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

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Determinate vs. IndeterminateShoot Growth

• Bush Snap Bean

• Trailing Pole Bean

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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

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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

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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

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ROOT GROWTH PATTERNS

• Variation in pattern with species and season
• Growth peaks in spring, late summer/early fall
• Spring growth from previous years foods
• Fall growth from summers accumulated foods
• Some species roots grow during winter
• Some species have some roots resting while, in
  the same plant, others are growing

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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

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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

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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

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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

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Light
• Temperature
• Water
• Gases

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Light
• Suns 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

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LIGHT LINKS

• http//www.physicalgeography.net/fundamentals/6hre
  volution.html
• http//vortex.plymouth.edu/sun/sun3d.html

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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

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Light (cont)
• importance of phytochrome in plant responses
• plants detect ratio of redfar-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

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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
• Cryptochrome and phototropin are compounds that
  react to blue light (320-400 nm)

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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

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Temperature
• correlates with seasonal variation of light
  intensity
• temperate-region growth between 39F and 122F
• 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

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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

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ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH

• Gases
• Nitrogen is most abundant (78)
• Oxygen (21) and carbon dioxide (0.035) 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

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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

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PHASE LINKS

• http//4e.plantphys.net/chapter.php?ch25
• http//www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd
  RetrievedbPubMedlist_uids10398702doptAbstrac
  t
• http//www.cnr.it/istituti/FocusByN_eng.html?cds0
  12nfocus4
• http//ipmb.sinica.edu.tw/senescence/intro.html

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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 (fig. 9-8, p. 177 T.
  9-4, p.178)
• 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

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PHASE CHANGE LINKAcacia melanoxylon Australian
Blackwood

• http//en.wikipedia.org/wiki/Acacia_melanoxylon

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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

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AGING LINKBristlecone Pine - Pinus longaeva
aristata

• http//sonic.net/bristlecone/home.html

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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

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REPRODUCTIVE GROWTH AND DEVELOPMENT

• Flower induction and initiation
• What causes a plant to flower?
• Daylength (photoperiod)
• Low temperatures (vernalization)
• Neither (most trees)

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REPRODUCTIVE GROWTH AND DEVELOPMENT

• Photoperiodism (fig. 9-10, p.180 T 9-5, p.181)
• 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 consumers expectations
  associated with seasons, e.g. poinsettias at
  Christmas

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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

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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

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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

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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)

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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

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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

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REPRODUCTIVE GROWTH AND DEVELOPMENT

• What if pollination and fertilization fail to
  occur?
• Fruit and seed dont develop
• Exception Parthenocarpy
• Formation of fruit without pollination/fertilizati
  on
• 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

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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

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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

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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)

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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