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The Biological Role of Abscisic Acid in ... - rideau.carleton


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									The Biological Role of Abscisic Acid in
    Precocious Seed Germination

 • Present by Collin Mecke
 • April 1st
 • 61.325
           Introduction to ABA
-Synthesis of ABA occurs in the chloroplasts and other
  plastids using the terpenoid pathway (fig 23.2)
• Detected in all parts of the plant
• Transported by both phloem and xylem
• Inhibits stomata opening
• Regulates seed and bud dormancy
             Discovery of ABA
• Unknown inhibitory compounds that effect the dormancy
  of seeds and buds were known about for a long period
• Inhibitory compounds that differed from auxin were
  discovered (1953)
• A substance that promotes abscission in cotton fruit was
  found ten years later and called Abscission II (1963)
• At the same time another compound that promoted bud
  dormancy was found and call Dormin
• These two substance (Abscission II and Dormin) were
  found to be identical and called Abscisic Acid.
         How is it Measured?

Bioassay-Measuring coleoptile growth inhibition.
         Minimum detection is 10-7 M
         -Closure of stomata (10-9M)
Physical Methods- Gas Chromatography (10-13g)
                 -High Performance Liquid
Immunoassay-Recognition of ABA by antibodies
   How ABA Causes Dormancy
• At high levels of ABA (just before dormancy occurs) late-
  embyrogenesis abundant proteins (LEA) are produced
• LEA’s are thought to be involved in desiccation tolerance
• ABA has been shown to affect the amount and
  composition of storage proteins in a double mutant of
  Arabidopis (aba/abi3-1) and ABA deficient mutants of
• This process is called embryo induced dormancy
        Precocious Germination

-Immature embryos were removed from seeds and cultured
midway through development (before the onset of dormancy)
-These embryos germinated precociously (without passing
through normal dormancy)
- When ABA was added to the medium precocious germination
did not occur.
               Further Evidence
• Zea maize has several mutant species; vp2, vp5 and vp7
  that are ABA deficient (fig 23.2)
• The embryos of these plants germinate precociously on the
  cob. This process is called viviparous.
• The addition of exogenous ABA prevented precocious
• Also, there is a vp1 mutant which is insensitive to ABA. It
  will germinate precociously even with the addition of
  exogenous ABA.
             Current Research
• It has been well documented that the absence of ABA
  causes precocious germination.
• Is a certain amount of GA required?
• Fluridone was used to cause ABA deficiency and
  paclobrutrazol or ancymidol to reduce GA in corn
• Measured the amount of GA in each seed and whether
  precocious germination occurred.
• It was found that a minimum amount of GA was required
  for precocious germination.
             Current Research
• vp5 maize mutant was cross with a dwarf maize (d1-GA
• The resulting double mutants (vp5/d1) did not undergo
  precocious germination
• Addition of exogenous GA to double mutant did produce
  precocious germination
             Current Research
•   Low levels of GA did not diminish vivipary in vp1
•   This suggests that the GA and ABA signaling converges
    upstream from the site of vp1 action.
•   It was proposed that vp1 controls seed maturation and
    germination through 2 processes;
    1. Transcriptional activator of ABA-inducible gene
    2. ABA-independent repressor of germination specific
       gene expression
              Uses in Bio-Tech
• Causing seeds to germinate faster (skipping the dormancy
  stage of development) will results in plants growing to
  maturity faster.
• This could result higher crop production.

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