Somatic Embryogenesis

1
Somatic Embryogenesis

• Occurs naturally in some plants
• Citrus, crabapple
• During formation of the zygotic embryo

2
Somatic embryogenesis in vitro

• May be induced from almost any somatic
• Critical aspects
• Bipolar
• Not attached to explant by vascular tissue

3
Applicable plants

• Has been induced in a wide variety of plants
• Coffee, many citrus, conifers, Kalanchoe pinnata,
  Cucurbita pepo, castor bean, barley, lolium,
  rice, lily, snapdragon, atropa belladonna,
  Petunia hybrida, rue, caraway, vitis, fennel,
  parsley.
• Most woody plants form somatic embryos only from
  chronologically young tissue such as cotyledons,
  hypocotyl etc. Spruce, walnut, pecan, ash

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Walnut somatic embryogenesis
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Individual walnut embryo
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Walnut somatic embryogenesis

• Wanut somatic embryos at different stages of
  devlopment

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Abnormal walnut somatic embryo
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Oak somatic embryogenesis
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Abnormal oak somatic embryo
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Abnormal oak somatic embryo
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Stages in somatic embryogenesis

• Induction
• Development and maturation
• Globular
• Heart stage
• Torpedo
• Germination (conversion)

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Induction

• Auxins required for induction
• Proembryogenic masses form
• 2,4-D most used
• NAA, dicamba also used

13
Development

• Auxin must be removed for embryo development
• Continued use of auxin inhibits embryogenesis
• Stages are similar to those of zygotic
  embryogenesis
• Globular
• Heart
• Torpedo
• Cotyledonary
• Germination (conversion)

14
Maturation

• Require complete maturation with apical meristem,
  radicle, and cotyledons
• Often obtain repetitive embryony
• Storage protein production necessary
• Often require ABA for complete maturation

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Maturation (cont.)

• ABA often required for normal embryo morphology
• Fasciation
• Precocious germination

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Effect of ABA on maturation of spruce somatic
embryos
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Germination

• May only obtain 3-5 germination
• Sucrose (10), mannitol (4) may be required
• Drying (desiccation)
• ABA levels decrease
• Woody plants
• Final moisture content 10-40
• Chilling
• Decreases ABA levels
• Woody plants

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Important factors

• Explant source
• Woody plants
• Immature zygotic embryos at a specific stage of
  growth
• Herbaceous plants
• More flexible - leaves, flower parts, stems

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Loss of potential in long-term cultures

• Genetic alteration
• Altered hormonal balane
• Competition from new, insensitive cells

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Effect of genotype
Genotype - critical!
Rice
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Effect of genotype in Pinus strobus somatic
embryogenesis
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Pinus strobus experiment repeated
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Medium

• Nutrients in medium - Nitrogen
• Reduced nitrogen
• NH4Cl used
• Use of KNO3 only gave no embryos
• May be required in induction and/or development

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Explant

• Age of explant
• Juvenile
• Often only zygotic embryos work - especially in
  woody plants
• Narrow window of development
• Eg.wheat between 11 and 14 days post-anthesis

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Theories to explain somatic embryogenesis

• Dedifferentiation
• Cell isolation theory
• Explant physiology and culture environment
• Intercellular communication and
  cytodifferentiation
• Predetermination
• Pre- and induced embryogenic determined cell
  theory

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Synthetic seed

• Potential method of clonal production
• Naked embryos fragile
• Must be encapsulated
• Calcium alginate
• Polyox