Control Systems in Plants

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Control Systems in Plants
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Plant Hormones

• What is a Plant Hormone ?
• Compound produced by one part of an organism that
  is translocated to other parts where it triggers
  a response in target cells and tissues.

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Functions of Plant Hormones

• Control plant growth and development by affecting
  division, elongation, and cell differentiation
• Effect depends on size of action, stage of plant
  growth and hormone concentration
• Hormonal signal is amplified by gene expression,
  enzyme activity, or membrane properties

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Table 39.1 An Overview of Plant Hormones
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Auxins(IAA) indoleacetic acid natural auxin in
plants

• Promotes elongation secondary growth
• Apical meristem is the major site of auxin
  production
• Inhibits lateral growth
• Induces female floral parts fruit

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Figure 39.8 Apical dominance with apical bud
(left), apical bud removed (right)
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Figure 39.7 Cell elongation in response to
auxin the acid growth hypothesis
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Cytokinins

• Move from the roots to tissues by moving up xylem
• Stimulates protein synthesis
• Made in roots
• Functions
• 1. Cell division and differentiation
• 2. Apical dominance
• 3. Anti-aging hormones
• slow protein deterioration

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Gibberellins

• Stimulate elongation of cells
• Inhibits root growth
• Stimulate flower part development- bolting
• Signals seeds to break dormancy and germinate

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Figure 39.9 Foolish seedling disease in rice
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Figure 39.11 The effect of gibberellin treatment
on seedless grapes
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Abscisic Acid (ABA)

• Growth inhibitor
• returns seeds to dormancy
• inhibits cell division in vascular cambium
• causes rapid closing of stoma during dry periods
• promotes positive geotropism

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Figure 39.12 Precocious germination of mutant
maize seeds
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Ethylene

• Gaseous hormone
• High auxin induces release of ethylene
• Causes senescence (aging)
• Fruit ripening one bad apple does spoil the
  whole bunch
• Abscission loss of leaves on
• deciduous trees

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Figure 39.16 Abscission of a maple leaf
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Which hormones cause the following.

• Apical dominance from apical bud
• Abscission
• Stimulates growth of axillary buds
• Root growth
• Stimulates closing of stomata
• Causes fruit ripening
• Stimulates seeds to break dormancy and germinate
• Growth inhibitor
• Cell division and differentiation
• Cell elongation
• Seedless fruit

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• Answers to Previous Slide
• Auxin
• Ethylene
• Cytokinins
• Cytokinins
• Abscisic acid
• Ethylene
• Gibberellins
• Abscisic acid
• Auxins and cytokinins
• Auxins
• Auxins

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Which hormone is made at each location?

• Made in roots and transported upwards
• Found in meristems of apical buds and seed
  embryos
• Found in tissues of ripening fruit
• Leaves stems, roots and green fruit

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• Answers to Previous Slide
• Cytokinins
• Auxins
• Ethylene
• Abscisic Acid

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Plant Movement

• A. Tropisms
• growth response toward or away from stimuli
• 1. Phototropism
• cells on darker side of shoot elongate faster
  than cells on bright side due to auxin
  distribution
• auxin move laterally across the tip from the
  bright to dark side by an unknown mechanism.
• Cells on the dark side grow

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• 2. Gravitropism (geotropism)
• gravity
• roots --gt positive geotropism
• stems---gt negative geotropism
• Statoliths
• starch grains in root cap cells, they trigger
  calcium redistribution which results in auxin
  movement in root
• auxin inhibits cell elongation
• upperside of root elongates faster than bottom

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• 3. Thigmotropism
• growth in response to touch
• tendrils contacts solid and coils
• increased production of ethylene
• 4. Hydrotropism
• growth toward water
• willow tree