Plant Growth Regulators (Cytokinins)

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Plant Growth Regulators(Cytokinins)

• 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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Cytokinins

• The word for cytokinins is a generic name for
  all naturally occurring substances that are known
  to promote cell division..
• These hormones may also be involved in
  controlling leaf senescence and the growth of
  lateral branches.
• The most active, naturally-occurring cytokinin is
  zeatin.
• Cytokinins occur in most plants including mosses,
  ferns, conifers, algae and diatoms.

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Cytokinins

• The most widely distributed cytokinins are the
  synthetic benzyladenine and kinetin. Kinetin was
  discovered from the tobacco pith callus and the
  chemical substance was identified as 6-furfuryl
  aminopurine. The natural cytokinin appears to be
  made principally in apical root meristem,
  inflorescences and developing fruits.

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Cytokinins

• Cytokinins have been found to be the constituent
  of certain transfer RNA molecules in a number of
  different organisms.
• They are also involved in stimulation of organ
  formation e.g. formation of leave, fruit, buds,
  and branches.
• They tend to contract or overcome apical
  dominance and break dormancy.
• They also enhance seed germination and uniform
  flowering.
• Cytokinins regulate the transportation of
  metabolites in the phloem.

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Cytokinins

• Where it produced?
• Cytokinins are synthesized primarily in actively
  growing tissues, particular in roots, embryos
  (seeds), geminating seeds, and young developing
  fruits and transported to other organs.
• This is known in part because roots can be
  cultured (grown in Artificial medium in flask)
  without added cytokinin, but stem cells cannot.

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Cytokinins

• Transport
• Cytokinins produced in the root reach to their
  target tissues by moving up the plant in the
  xylem sap (transpiration stream).
• Zeatin ribosides are the main transport form
  converted to the free base or glucosides in the
  leaves.
• Some cytokinins also moves in the phloem.

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Cytokinins

• Interact with auxins to influence differentiation
  of tissues (may be used to stimulate bud
  formation).
• Liquid endosperm of coconut called Coconut Water
  / Milk contain cell division causing factors
  (Kinetine).
• Similarly the developing endosperm of maize
  contain such factors (Zeatin).
• As roots begin to grow actively in the spring,
  they produce large amounts of cytokinins that are
  transported to the shoot, where they cause the
  dormant buds to become active and expand.
• Tissue cultures use cytokinins to induce shoot
  development.
• Cytokinins may slow or prevent leaf senescence
  (leaf ageing or leaf fall).

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Cytokinins Actions

• 1- Regulates the cell cycle/cell division
• Cytokinin will stimulate cell division and
  influenced the pathway of differentiation when
  acting with auxin hormone.
• In some experment, a piece of paranchyma tissue
  from stem is cultured. This is some observation
  of the effect on cytokinin in cell tissue

Absent of cytokinin Added cytokinin auxin Added cytokinin only
The cell grow very large but do not divided The cell is grow and divided No effect
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How Cytokinins Control Cell Division?

• The ratio of cytokinins to auxin controls the
  cell differentiate.
• When the concentration of these two hormone are
  at certain level, the mass of cell continues to
  grow, but remains undifferentiated called a
  callus.

Cytokinin level increase Auxin level increase
Shoot buds develop from callus Root form
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Cytokinins Actions

• 2- Control morphogenesis
• In plant tissue cultures, cytokinin is required
  for the growth of callus (an undifferentiated,
  tumor-like mass of cells)

The Medium The Callus differentiation
Callus Auxin No Cytokinin Little growth of callus
Callus Auxin Cytokinin Callus grows well, undifferentiated

• Ratio of cytokinin and auxin are important in
  determining the fate of the callus

The concentration THE Callus differntiation
Callus Low cytokinin/ auxin Little growth of callus
Callus high cytokinin / auxin Callus grows well, forms meristem shoots
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• 2- Control morphogenesis

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Cytokinins Actions

• 3- Bud development
• Direct application of cytokinin promotes the
  growth of axillary buds.
• Exogenous cytokinin and auxin are thus
  antagonistic in their effects on axillary bud
  growth

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Cytokinins Actions

• 4- Delay senescence
• Senescence is the
• programmed aging process
• that occurs in plants.
• Loss of chlorophyll, RNA, protein and lipids.
• Cytokinin application to an intact leaf markedly
  reduces the extent and rate of chlorophyll and
  protein degradation and leaf drop.

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Cytokinins Actions

• 5- Greening
• Cytokinins promotes the light-induced formation
  of chlorophyll and conversion of etioplasts to
  chloroplasts (greening process).

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Cytokinins Actions

• 6- Promote cell expansion
• Cytokinins stimulate the expansion of cotyledons.
• The mechanism is associated with increased
  plasticity of the cell wall, not associated with
  acidification.

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• 6- Promote cell expansion

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Physiological effects of cytokinins
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Physiological effects of cytokinins
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