Chapter 6 Vegetative and Reproductive Growth and Development

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Chapter 6- Vegetative and Reproductive Growth and
Development
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• Root functions

• 1. Anchor plants

• 2. Absorb water
• and mineral nutrients

• 3. Conduct water,
• dissolved materials
• and organic materials

• 4. Store food materials

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Shoot and Root Systems

• Some roots also serve as a means of vegetative
  reproduction.
• Shoot growth tends to balance root growth

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Plant Growth

• Plant growth is defined as size increase by
  cell division and enlargement, including the
  synthesis of new cellular material and
  organization of subcellular organelles
• Many different measurements
• fresh weight, dry weight, volume, and size

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Determinate VS Indeterminate Growth

• When plants form flowers at the shoot terminals
  after a period of vegetative growth, and most
  shoot elongation ceases the growth pattern is
  determinate.
• A determinate plant grows for a specific period
  of time (even in the best environment), flowers,
  and dies. 1

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• When plant shoots continue to elongate, and
  flowers are produced on leaf axils the growth
  pattern in indeterminate.
• An indeterminate plant could theoretically live
  forever, if it had the perfect environment and
  was undisturbed. 1

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Annuals, Biennials, and Perennials

• Annuals - herbaceous plants that complete their
  lifecycle seed to seed in one growing season.
• Biennials -herbaceous plants that complete their
  lifecycle seed to seed in two growing seasons-
  not necessarily two years.
• Most biennials die shortly after flowering.
• Perennials- can be either woody or herbaceous
  plants that survive many years.

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Woody Perennial Shoot Growth Patterns

• Single flush/ formation of terminal resting bud-
  most common in our area.
• Oaks, conifers, most fruit trees
• Multiple flush/ formation of terminal resting bud
  after each.
• Subtropical species
• Single flush/shoot tip abortion at season end-
• elm, birch, willow, honeylocust also common in
  our area.
• Sustained flush/ formation of terminal resting
  bud at seasons end

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Root Growth Patterns

• Generally root growth in deciduous woody
  perennials
• greatest in the spring,
• second peak in late summer or early fall.
• However, some species roots may grow nearly any
  time of year.
• Root growth in deciduous woody perennials
• coincides with high levels of accumulated
  carbohydrates.

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Genetic Control of Growth

• Structural genes- genes involved in protein
  synthesis
• Regulatory or operator genes- involved in turning
  genes on and off

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Environmental Factors Affecting Plant Growth

• Light- influences
• 1. Phototropism which is the bending of stems,
  leaves and flowers toward light .
• Phototropism is thought to be caused by auxin
  accumulation on the dark side of stems.
• http//koning.ecsu.ctstateu.edu/Plant_Physiology/p
  hototropism.html
• Stomate opening and closing is another function
  partially controlled by light wavelength (color).

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Environmental Factors Affecting Plant Growth

• 2. Photoperiodism - responses triggered by
  variation in length of light and dark periods.
• Acclimation, flowering, and tuber formation may
  all be photoperiodic responses.
• http//koning.ecsu.ctstateu.edu/Plant_Physiology/p
  hotoperiodism2.html
• Acclimation- the physical and physiological plant
  processes in plants which prepare them for
  winter.

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Temperature

• Growing days or degree days -can be used to
  determine when or if a crop will mature in a
  given area.
• Degree days
• calculated by taking the mean (average)
  temperature in a day and subtracting 40 for cool
  season crops or 50 for warm season crops

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Temperature

• Example for one day
• high- 80 low- 60 Mean 70 40 30 degree days
  for cool season crops
• http//www.ent.iastate.edu/ipm/icm/1998/4-6-1998/d
  d.html

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Temperature

• Temperate plants -grow in a range of temperatures
  from 39-122 degrees Fahrenheit
• 1220 F protoplasm is destroyed
• Solarization- the conversion of light energy to
  heat , can cause cell destruction

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Temperature

• At the low end of the range chemical reactions
  and cellular activity nearly cease
• Below freezing membrane disruption by
  intracellular ice formation can cause cell death

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Water

• Plants are about 90 water by weight
• Water -a raw material for photosynthesis and
  medium for many chemical reactions in plants
• Water is used for plant growth cell expansion
• Water- used for plant cooling- transpiration
• What is evapotranspiration?
• http//www.ianr.unl.edu/pubs/irrigation/g992.htmW
  HATIS

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Gases

• Gases-
• The most important gases for plant growth are CO2
  and O2
• Carbon dioxide-the carbon source used in sugar
  and carbohydrate formation
• CO2 regulates the opening and closing of stomata-
  
• CO2 less than 300 ppm opens stomata if other
  environmental factors are favorable

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Gases

• Oxygen (O2) is essential for respiration of both
  plants and animals
• Oxygen is given off as a final product of
  photosynthesis

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Pollutant Gases

• Many gases result from the burning of fossil
  fuels and manufacturing
• Sulfur dioxide can cause acid rain
• Carbon dioxide can be used by plants but it is
  also a greenhouse gas

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Pollutant Gases

• Ozone, ethylene and peroxyacetal nitrates (PAN)
  can cause plant injury
• http//www.aces.edu/department/extcomm/publication
  s/anr/anr-913/anr-913.html

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Phase Change

• Plants go through phase changes just as animals
  do
• Plant appearance can change dramatically as they
  age
• For example
• A plant may have alternate leaves as a juvenile
  and opposite leaves as an adult
• A plant may have lobed leaves as a juvenile and
  leaves without lobes as an adult

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Phase Change

• Important physiological changes also occur as
  plants mature including
• The ability to be induced to flower
• Reduction or loss of ability to form adventitious
  roots

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Senescence

• Senescence - an irreversible deterioration
  leading to cellular breakdown and death.
• Flowering and fruit production use up stored
  nutrients and increases the rate of senescence
• http//www.worc.ac.uk/departs/envman/courses/hort/
  teach.hor/BSC/321/scen.html

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Reproduction and Development

• Fruit and seed production can occur only after a
  period of maturation in most plants.
• Phases following maturation include

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Reproduction and development
Induction
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Induction and Initiation

• Induction -the phase in which chemical changes
  that begin the flowering process take place in
  the plant in response to certain environmental
  conditions.
• Initiation - the transformation of the stem apex
  from a vegetative axis to a flowering culm.

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Types of Induction

• Photoperiodic induction - induction by changes in
  day length
• Plants induced to flower by decreasing the light
  period are called short day plants.
• Plants induced to flower by increasing the light
  period are called long day plants.
• In some plants flowering is not affected by day
  length day neutral plants.

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Photoperiodism

• It is actually the length of the dark period
  which is critical.
• If night is interrupted by a brief light period
  short day plants will not flower even if the
  total of the two light periods is less than the
  short day requirement.
• The leaf is thought to be the receptor for the
  light stimulus with the signal being transferred
  to the apical meristem.

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Phytochrome

• Phytochrome is the pigment in plants which is the
  receptor for the light signal.
• Phytochrome has two forms Pr and Pfr

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Phytochrome

• Pfr is the active form created when Pr is
  exposed to red light (660 nm)
• Pr is the inactive form which is created
  instantaneously when Pfr is exposed to far red
  light ( 730 nm).
• Pr is also created slowly as Pfr breaks down
  overnight in the dark.

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Pr
RED LIGHT
Pfr
FAR-RED LIGHT (instantaneous) OR DARKNESS (slow)
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Low Temperature Induction

• Low temperature induction vernalization
• Temperatures for vernalization generally fall in
  the 32-50 F
• (0-10 C) range.

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Low Temperature Induction

• Amount of time and the temperature required
  varies with species.
• Many plants including fruit trees require cold
  temperatures to overcome a rest period, not
  actually to induce flowering.

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Low Temperature Induction

• Bulb plants like tulips, crocuses and hyacinth
  require low temperatures to promote flower
  development.
• http//www.territorial-seed.com/links/techsheets/t
  ech_forcing.html
• Olives and Kiwis do require cold temperatures for
  induction.

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Flower Development

• The number of inductive cycles needed for flower
  initiation can vary from one to many depending on
  the species.

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Flower Development

• Induction to anthesis (flower opening) times vary
  greatly between species also.
• Development can be accelerated somewhat by
  increasing temperature with many plants.

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Pollination

• Pollination is the transfer of pollen from an
  anther to a stigma.
• Self-fertile plants can produce fruit and set
  seed with their own pollen, self- sterile plants
  can not

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Pollination

• Wind and Insects (especially bees) are the most
  common pollinating agents.

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Fertilization

• Angiosperms undergo double fertilization.
• One sperm nucleus unites with the egg to form the
  zygote.
• One sperm nucleus unites with two polar nuclei
  and forms the endosperm.

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Double fertilization

• Double fertilization is when the pollen tube
  enters the ovule through the micropyle and
  ruptures. One sperm nucleus fuses with the egg
  forming the diploid zygote. The other sperm
  nucleus fuses with the polar nuclei forming the
  endosperm nucleus. Most angiosperms have two
  polar nuclei so the endosperm is triploid (3n).
  The tube nucleus disintegrates. The food in the
  cotyledons is derived from the endosperm which,
  in turn, received it from the parent sporophyte.
  In many angiosperms (e.g., beans), when the seeds
  are mature, the endosperm has been totally
  consumed and its food transferred to the
  cotyledons. In others (some dicotyledons and all
  monocotyledons), the endosperm persists in the
  mature seed.

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Fruit Set

• Fruit set must not be too heavy or too light if a
  crop is to be profitable.
• Plant hormones including auxins, gibberillins and
  cytokinins can induce fruit set in different
  plants.
• Temperature at the time of fruit set is also
  critical- too low or too high can result in crop
  failure.

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Fruit Growth and Development

• Plant hormones including cytokinins,
  gibberellins, ethylene and auxins are involved in
  different phases of fruit development.
• Auxins appear to affect fruit size increase-
  strawberries
• After the initial period of intense cell
  division, increase in fruit size is due mainly to
  cell enlargement

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Plant Growth Regulators

• A plant hormone a substance produced in minute
  amounts at one site in the plant and translocated
  to another site where it alters growth and
  development.
• Plant growth regulators include plant hormones
  (natural and synthetic) and other non-nutrient
  chemicals that when applied to plants influence
  their growth and development.

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Plant Growth Regulators

• http//www.plant-hormones.bbsrc.ac.uk/education/ke
  nf.htm

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Plant Hormones

• Auxins- the first group of plant hormones to be
  discovered.
• Auxins influence
• cell enlargement or elongation
• apical dominance
• root initiation
• photo- and geotropism
• abscission of plant parts
• flower initiation and development
• fruit set and growth
• cambial activity
• tuber and bulb formation
• seed germination.

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Plant Hormones

• Auxins -synthesized in the in meristems and
  developing tissues and transported basipetally
  (toward the roots)
• Auxins are involved in apical dominance which
  is the suppression of growth of lateral buds.
• http//koning.ecsu.ctstateu.edu/apical/apical.html

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Plant Hormones

• IAA indoleacetic acid is a naturally occurrring
  auxin.
• Synthetic auxins
• IBA- indolebutyric acid,
• NAA-napthaleneacetic acid
• 2,4- dichlorophenoxyacetic acid are synthetic
  auxins

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Auxins- Commercial Uses

• Adventitious root initiation- IBA and NAA are
  used as dips to promote rooting of cuttings.
• http//www.hortus.com/drydip.htm
• Weed control- 2,4-D is an effective and
  inexpensive selective broadleaf weed killer
• http//www.ianr.unl.edu/pubs/pesticides/g802.htmS
  YMPT
• http//www.24d.org/
• http//ace.ace.orst.edu/info/extoxnet/pips/24-D.ht
  m

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Auxins- Commercial Uses

• Inhibition of stem sprouting- NAA at 10,000 ppm
  is effective in preventing sprouts at the base of
  ornamental trees.
• Tissue culture- IAA or 2,4-D are used in tissue
  culture media to initiate adventitious roots

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Suckering on a silver maple
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Gibberellins

• Gibberellins are synthesized in the shoot apex,
  especially in leaf primordia.
• Gibberellins (GA) can stimulate cell division and
  elongation as well as enzyme secretion.

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Gibberellins

• GA may also be involved in flower initiation,sex
  expression, fruit growth maturation and ripening.
• GA stimulates enzymes in the aleurone layer which
  hydrolyze stored materials for the embryo to
  utilize in germinating seeds
• http//www.plant-hormones.bbsrc.ac.uk/education/ke
  nf.htm

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Agricultural Uses for GA

• Increasing the fruit size of seedless grapes-
  20-40 ppm GA is sprayed on grapes at fruit set
  stage to increase berry size.
• Stimulating seed germination and seedling growth-
  soaking seeds in solutions of 20- 10,000 ppm GA
  has been shown to increase seedling emergence and
  growth in many plants.

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Agricultural Uses for GA

• Promoting male flowers in cucumbers- GA applied
  to leaves stimulates male flower development
  needed for pollen for breeders.
• Overcoming cold requirement for some plants- for
  azalea and cyclamen GA can be substituted for
  cold treatments to stimulate flower development.

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Cytokinins

• Roots supply cytokinins to shoots.
• Cytokinins promote cell division.
• Cytokinins are also involved in cell enlargement,
  tissue differentiation, dormancy, flowering,
  fruiting, and retardation of leaf senescence.
• Benzyladenine (BA) is a synthetic cytokinin that
  is used to promote shoot growth in tissue
  culture.

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Ethylene

• Ethylene is gas which diffuses readily throughout
  the plant.
• Ethylene is produced in actively growing
  meristems, ripening and senescing fruit,
  senescing leaves, germinating seeds and certain
  plant tissues when they are injured.
• Ethephon is chemical that releases ethylene when
  it is applied to a plant.

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Ethylene Uses

• Fruit ripening- used on bananas, tomatoes and
  honeydew melons.
• Flower initiation- used commercially on various
  ornamental bromliads.
• freephotos4u.com/garden/bromliad.html
• Growth retardant- the product Proxy is used to
  slow the growth rate of turfgrass to reduce the
  need for mowing.

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Ethylene Uses

• Changing sex expression-
• can dramatically increase the percentage of
  female flowers in cucumbers and pumpkins for
  better yields.

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Ethylene Uses

• Degreening citrus- ethylene treatment breaks down
  the chlorophyll in the rinds to make fruit
  attractive for market.
• Harvest aid- ethylene can make fruit and nuts
  separate more easily from the tree.

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Ethylene for causing fruit drop
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Harmful Effects of Ethylene

• Leaf abscission and flower senescence- Can be
  caused by ethylene, keep cut flowers away from
  ripe fruit.
• Flower bud abortion- if tulips or other bulb
  crops are exposed to ethylene from a rotting
  bulb, they will probably abort their flower bud
  and not bloom.
• Accelerated fruit ripening- one bad apple spoils
  the barrel

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Abscisic Acid (ABA)

• ABA is involved in fruit and leaf abscission,
  onset of dormancy in seeds and early stages of
  vegetative and flower bud rest in woody
  perennials.
• No commercial use for ABA to date.
• http//www.sidwell.edu/sidwell.resources/bio/Virtu
  alLB/plant/hormone.html

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Other Inhibitors

• Most commercially used growth inhibitors work by
  inhibiting GA slowing cell division and/ or cell
  elongation.
• Reduced internode length results in more compact
  plants.
• Growth retardants are used extensively in flower
  production and in turfgrass management.

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Commercial Growth Retardants

• Diaminozide- trade names Alar, B-Nine
• -Alar was used to enhance fruit size and
  appearance, now outlawed by EPA
• -B-Nine still used extensively for bedding
  plants and mums.
• Chlormequat- trade names CCC, Cycocel
• -Used for height control of geraniums,
  Ponsettia, azalea and some bedding plants.
• -Also used to prevent lodging in wheat.

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Commercial Growth Retardants

• Ancymidol- trade name A-Rest
• -Used for height control of potted bulbous
  plants and mums.
• Paclobutrozol- trade names Bozii, Scotts TGR
• -Used for bedding plant production and turfgrass
  growth regulation.

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Presentation adapted from

• Hartmann, et al 1988. Plant Science, Second
  Edition, Englewood Cliffs, N.J. Prentice- Hall.
• Other References
• 1.http//www.gardenwithinsight.com/help100/0000039
  3.htm