Plant Responses to Internal and External Signals

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• Plant Responses to Internal and External Signals

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What is tropism?

• The directional growth of plant organs in
  response to a directional environmental stimulus
• Trop ism
• From the Greek a turning

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Plant Respond to light

• Phototropism responses involve bending of
  growing stems toward light sources.
• Individual leaves may also display phototrophic
  responses.
• auxin most likely involved

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Plants Respond to Gravity

• Gravitropism is the response of a plant to the
  earths gravitational field.
• present at germination
• auxins play primary role
• Four steps
• gravity perceived by cell
• signal formed that perceives gravity
• signal transduced intra- and intercellularly
• differential cell elongation

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Plants Respond to Touch

• Thigmotropism is directional growth response to
  contact with an object.
• tendrils

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Other Tropisms

• Electrotropism - electricity
• Chemotropism - chemicals
• Traumatropism - wounding
• Thermotropism - temperature
• Aerotropism - oxygen
• Skototropism - dark
• Geomagnetotropism - magnetic fields

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How do tropisms work

• How do plants detect light and gravity touch of
  something else?
• How do plants roots and shoots bend?

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In all tropism and bending is the result of
unequal cell elongation