10.4 HORMONES IN PLANTS

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10.4 HORMONES IN PLANTS

• By the end of the lesson, students should be able
  to
• explain the roles of hormones in plants
• Auxins
• Gibberellins
• Cytokinins
• Abscisic acid
• Ethylene

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Auxin

• Produced in
• Embryo of seed, meristem of apical buds, young
  leaves
• Roles
• stimulates stem elongation (low concentration
  only), root growth, cell differentiation and
  branching
• regulates development of fruit
• enhances apical dominance
• functions in phototropism and gravitropism
• promotes xylem differentiation
• retards leaf abscission

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• Auxin is synthesized in the shoot tip and
  migrates down the stem
• Auxin stimulates cell elongation causing the
  shoot to grow toward light

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• High concentration of auxin will inhibit shoot
  growth
• A certain concentration causes shoot growth is
  inhibiting root growth

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Phototropism
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Gravitropism
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Stem elongation
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Gibberellins

• Produced in
• Meristems of apical buds and roots, young leaves,
  embryo
• Roles
• promotes seed and bud germination
• stem elongation and leaf growth
• stimulate flowering and development of fruit
• affect root growth and differentiation

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Types of Germinations
Seed Germination
Buds Germination
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Flowering
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Cytokinins

• Produced in
• roots and transported to other organs
• Roles
• affect root growth and differentiation
• stimulate cell division and growth
• stimulate germination
• delay senescence

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Abscisic acid

• Produced in
• Leaves, stems, roots and green fruit
• Roles
• inhibits growth
• closes stomata during water stress
• promotes seed dormancy

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Seed dormancy
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Ethylene

• Produced in
• tissue of ripening fruit, nodes of stems, aging
  leaves and flower
• Roles
• promotes fruit ripening, opposes some auxin
  effects
• promotes or inhibits growth and development of
  roots, leaves and flowers, depending on species

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Fruit ripening
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