Download Plant Responses Signal Transduction Pathway Tropisms Tropisms

Botany: Part IV Plant Signaling STUDENT HANDOUT
Plant Responses
Tropisms
Signal Transduction Pathway
Plant hormones trigger a signal
transduction pathway
A tropism is the
turning or bending
movement of an
organism or a part
toward or away from
an external stimulus,
such as light, heat, or
gravity.
Botany: Part IV
Plant Signaling
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Tropisms
Phototropism
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Plant Response to Light
Plant Hormones
What are
these plants
responding
to?
• Auxins- stimulate cell elongation, responsible
for tropisms
• Cytokinins-stimulate cytokinesis or cell
division, and cell differentiation
• Gibberellins- stimulate cell elongation in stems
• Abscisic Acid-promotes seed dormancy, slows
growth
• Ethylene- gas, promotes ripening of fruit and
cell death
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Short-Day Plants
Long-Day Plants
• Photoperiodism is the physiological reaction
of organisms to the length of day or night.
• Short-day (long-night) plants flower when night
exceeds a critical dark period.
• A flash of light interrupting the dark period prevents
flowering.
• Examples: Chrysanthemums, poinsettias and some
soybean plants generally flower in late summer, fall or
winter.
• Long-day (short-night) plants flower only if the night is
shorter than a critical dark period.
• A brief flash of light artificially interrupts a long dark period,
thereby inducing flowering.
• Examples: spinach, radishes, lettuce, irises and many cereal
varieties are long-day plants.
• In the 1940s researchers learned
photoperiodism is controlled by night length.
Plants can detect light’s direction, intensity, and
wavelength. Light receptors are called
phytochromes.
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Photoperiodism
• It occurs in plants and animals.
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Photoperiodism
• To flower or
not to
flower?
That is the
question.
(Apologies to
Shakespeare)
• Photoperiodism can also be defined as the
developmental responses of plants to the
relative lengths of the light and dark periods.
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Gravitropism
Geotropism (or Gravitropism)
Thigmotropism
Response to Other Stimuli
• Thigmotropism is a movement in which a
plant moves or grows in response to
touch or contact stimuli.
• Geotropism or gravitropism
turning or growth movement
by a plant or fungus in
response to gravity.
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