Plant Hormones

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Plant Hormones

• Darwins idea

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Plant hormones are chemical messengers of
homeostasis

• They are
• Organic compounds
• Effective at very low concentration
• Synthesized in one part of the plant and
  transported to another
• Interactive with specific target tissues to cause
  physiological responses
• There are five major groups of plant hormones

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Make a table for the following information
Hormone Stimulates
Auxins
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Auxins

• Stimulates
• cell elongation
• cell division
• differentiation of phloem and xylem

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Abscisc Acid

• Stimulates
• closure of stomata
• seeds to synthesize storage proteins.
• induction and maintenance of dormancy.
• gene transcription in response to wounding

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Cytokinin

• Stimulates
• cell division
• morphogenesis
• growth of lateral buds
• leaf expansion
• chlorophyll synthesis.

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Ethylene

• Stimulates
• shoot and root growth and differentiation (triple
  response)
• leaf and fruit abscission (falling off plant)
• flower opening
• fruit ripening

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Gibberellins

• Stimulate
• stem elongation
• enzyme production (a-amylase) in germinating seeds

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Plant movement

• Is a response to environmental stimuli such as
  light, gravity and mechanical disturbances.
• Movements fall into two groups
• tropisms and nastic movements.

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TROPISM

• Plant movement determined by direction of an
  environmental stimulus.
• Movement toward an environmental stimulus is
  called a positive tropism and away is called
  negative tropism.
• Each kind of tropism is named for its stimulus
• Example positive phototropism

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Phototropism
Stimulus Hormone Response
Light Auxins move to shaded side of plant Cells on shaded side elongate causing plant to bend towards light
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Thigmotropism
Stimulus Hormone Response
Touching a solid object Auxin and ethylene Tendrils and stems coil, allows vine to climb, increasing interception of sun
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Gravitropism
Stimulus Hormone Response
Gravity Auxins Roots positively gravitropic auxins accumulate on lower side of root cells inhibits elongation, so roots grow down.
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Stem negatively gravitropic auxins accumulate on lower side of stem stimulate elongation so stem grows up
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Chemotropism
Stimulus Hormone Response
Chemical ??? Plant will grow towards or away from source.
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Task

• Read the information provided and make a chart to
  show two types of Nastic movement
• Thigmonastic
• Nyctinastic