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GROWTH RESPONSES AND BIOLOGICAL RHYTHMS IN PLANTS CH 33

GROWTH RESPONSES AND BIOLOGICAL RHYTHMS IN PLANTS CH 33. Tropisms orient plant growth toward or away from environmental stimuli Plants sense and respond to environmental changes In a variety of ways. Light. Tip covered by opaque cap. Base covered by opaque shield. Tip separated

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GROWTH RESPONSES AND BIOLOGICAL RHYTHMS IN PLANTS CH 33

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  1. GROWTH RESPONSES AND BIOLOGICAL RHYTHMS IN PLANTSCH 33 • Tropisms orient plant growth toward or away from environmental stimuli • Plants sense and respond to environmental changes • In a variety of ways

  2. Light Tip covered by opaque cap Base covered by opaque shield Tip separated by mica Tip separated by gelatin block Tip covered by trans- parent cap Tip removed Control Darwin and Darwin (1880) Boysen-Jensen (1913) • Response to Light • Phototropism- bending in response to light • May result from auxin moving from the light side to the dark side of a stem

  3. Response to Gravity • A response to gravity, orGravitropism • May be caused by the settling of special organelles on the low sides of shoots and roots • This may trigger a change in the distribution of hormones Figure 33.9A

  4. Response to Touch • Thigmotropism, a response to touch • Is responsible for the coiling of tendrils and vines around objects Figure 33.9B

  5. Plants mark the seasons by measuring photoperiod • Photoperiod • Is the relative lengths of night and day • The timing of flowering • Is one of the seasonal responses to photoperiod

  6. 24 Darkness Critical night length Flash of light Time (hr) Light 0 Long-day (short-night) plants Short-day (long-night) plants • Plants whose flowering is triggered by photoperiod fall into two groups • Short-day (long-night) plants • Long-day (short-night) plants Figure 33.11

  7. Phytochromeis a light detector that may help set the biological clock • Phytochromes are proteins with a light-absorbing component • That may help plants set their biological clock and monitor photoperiod

  8. 24 Darkness Critical night length Flash of light Time (hr) Light 0 Long-day (short-night) plants Short-day (long-night) plants Results

  9. 4 5 Recruitment of wasp Wasp lays eggs 3 Synthesis and release of chemical attractants 1 2 Damage to plant and chemical in caterpillar saliva Signal transduction pathway • Defenses Against Herbivores • Some plants recruit predatory animals • To help defend them against certain herbivores Adapted from Edward Farmer, “Plant Biology: New Fatty Acid–Based Signals: A Lesson from the Plant World” Science 276 (1997), p. 912. 1997 American Association for the Advancement of Science. Plant cell Figure 33.14A

  10. PLANT DEFENSES • Defenses against herbivores and infectious microbes have evolved in plants • Plants use chemicals • To defend themselves from both herbivores and pathogens

  11. Local defenses include • Microbe-killing chemicals and sealing off the infected area • Hormones • Trigger generalized defense responses in other organs (systemic acquired resistance)

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