The biological role of abscisic acid in precocious seed germination
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The Biological Role of Abscisic Acid in Precocious Seed Germination. Present by Collin Mecke April 1 st 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

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The biological role of abscisic acid in precocious seed germination
The Biological Role of Abscisic Acid in Precocious Seed Germination

  • Present by Collin Mecke

  • April 1st

  • 61.325


Introduction to aba
Introduction to ABA Germination

-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
Discovery of ABA Germination

  • 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
How is it Measured? Germination

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 Chromatography

Immunoassay-Recognition of ABA by antibodies

(10-13g)


How aba causes dormancy
How ABA Causes Dormancy Germination

  • 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 maize.

  • This process is called embryo induced dormancy


Precocious germination
Precocious Germination 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
Further Evidence Germination

  • 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 germination.

  • Also, there is a vp1 mutant which is insensitive to ABA. It will germinate precociously even with the addition of exogenous ABA.


Current research
Current Research Germination

  • 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 research1
Current Research Germination

  • vp5 maize mutant was cross with a dwarf maize (d1-GA deficient)

  • The resulting double mutants (vp5/d1) did not undergo precocious germination

  • Addition of exogenous GA to double mutant did produce precocious germination


Current research2
Current Research Germination

  • Low levels of GA did not diminish vivipary in vp1 mutants.

  • 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

    expression

    2. ABA-independent repressor of germination specific

    gene expression


Uses in bio tech
Uses in Bio-Tech Germination

  • 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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