Plant Growth Regulators (Gibberellins)

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Plant Growth Regulators(Gibberellins)

• Prof. Dr./ Galal Ismail Eliwa
• Head Of Pomology Department

Faculty Of Agriculture Damietta University
E. mail/ geliwa2002_at_du.edu.eg
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Gibberellins

• Gibberellins are plant hormones that promote
  growth, seed germination and leaf expansion.
• They occur at low concentrations in vegetative
  tissues but at higher concentration in
  germinating seeds.
• Induce cell elongation and cell division.
• Important for plant growth and development
  through flowering and/ or seed germination.

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Gibberellins

• Discovered by Kurosawa, a Japanese Plant
  Pathologist in 1928.
• Rice plants infected by the fungus Gibberella
  fujikuroi showed excessive stem elongation.
• Symptom is called Bakane diseases foolish
  seedling .
• Chemical was extracted purified and names as
  Gibberellic Acid (GA)
• Now 84 different Gibberellins are available GA1
  to GA84.
• The most commonly occurring gibberllinis is GA3

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Gibberellins
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Gibberellins
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Gibberellins

• Site
• Are produced in the shoot apex primarily in the
  leaf primordial (young leaves), roots, and
  developing seeds (developing endosperm) and
  fruits.
• Transport
• Made in the tissue in which it is used.
• Transport occurs through Xylem, Phloem, or cell
  to cell.
• Phloem seems to be most important route.
• Transport is not polar, as it is for Auxin.

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Gibberellins Actions

• Promotes stem elongation
• Stimulates cell division, cell elongation (or
  both) and controls enzyme secretions. EX dwarf
  cultivars can be treated with GA and grow to
  normal heights indicates dwarf species lack
  normal levels of GA.
• dwarf short.,
• wild type tall
• dwarf GA tall
• Thus, Ga application
• stimulates elongation and
• acts on intact plants.

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Gibberellins Actions
1- Promotes stem elongation
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Gibberellins Actions in Tissue culture
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Gibberellins Actions in Tissue culture
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Gibberellins Actions

• 2- Overcomes dormancy in seeds
• Gibberellins also have a fundamental role in
  breaking seed dormancy and stimulating
  germination.
• The endosperm of many seeds contains protein and
  carbohydrate reserves upon which a developing
  embryo relies for energy and nutrition.
• These reserves must be mobilized and transported
  to the embryo.
• A range of hydrolytic and proteolysis enzymes
  break down endosperm starches and proteins into
  smaller, more easily transported molecules, such
  as sugars and amino acids.

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Gibberellins Actions

• Overcomes dormancy in seeds

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Gibberellins Actions improve germination ???????
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Gibberellins Actions improving seeds germination
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Gibberellins Actions

• Involved in parthenocarpic fruit development

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Gibberellins Actions
GA can induce fruit enlargment

• Gibberellins stimulate the stalk length of
  seedless grapes to grow longer, thereby
  alleviating compaction and it promotes elongation
  of the fruit.

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• Gibberellins Actions improving pome fruit set
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  5-10 ??? ?? ??????? (3-6 ??? / 600 ??? ???) ???
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  50-75
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Gibberellins Actions

• Promotes cell division elongation

Red Delicious apples untreated (Left) and treated
with a combination of benzyladenine, a cytokinin,
and GA4 GA3 (Right). Note The elongated almost
pointed shape.
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Gibberellins Actions improving pome fruit set
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• ?? ????????? ????? 10 ??? ?? ??????? ??? 30 -
  40 ?????.
• (1 ??? / 100 ??? ??? ???????? ?? ???? ?????
  ?????? ???? ????).

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Gibberellins Actions

• Flowering
• GA stimulates bolting in Long Day plants and can
  substitute for long days or cold treatments that
  are necessary for flowering.

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Gibberellins Actions

• Sex expression
• In plants with separate male and female flowers,
  GA application can determine sex.
• For example, in cucumber and spinach, GA
  treatment increases the proportion of male
  flowers for seed production.
• In maize, GA treatment causes female flower
  development.

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Gibberellins Actions

• High sugar yield
• Growing of sugarcane enhances the growth of
  internodes and increase the crop productivity
  sugar yield of crop.

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Effect of pre-sowing seed treatment with
bio-regulators (GA3)
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Effect of Gibberellins on fruit set and
development
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Thank you for your attention