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Control Systems in Plants

Control Systems in Plants. Chapter 26. Control of Plant Development plant hormones chemical messengers within organisms each has a very specific function auxins promote growth at apical meristems cause growth in different directions gibberellins promote stem elongation cytokinins

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Control Systems in Plants

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  1. Control Systems in Plants Chapter 26

  2. Control of Plant Development • plant hormones • chemical messengers within organisms • each has a very specific function • auxins • promote growth at apical meristems • cause growth in different directions • gibberellins • promote stem elongation • cytokinins • promote cell division • prevent premature aging (senescence) • ethylene • causes dropping of leaves and fruit (abscission) • ripens fruit • abscisic acid • promotes seed and bud dormancy • closes stomata

  3. Plant Responses to the Environment • tropisms • growth toward or away from a variable • positive vs. negative • causes growth in different directions • phototropism, chemo-, thigmo-, gravi- Fig. 26.11 (a) Negative gravitropism in stem growth. (b) Positive gravitropism in root growth. An example of positive phototropism

  4. circadian rhythms • activities that occur in 24-hour cycles • biological clocks • internal (genetic) mechanism that maintains circadian rhythms • strongly influenced by photoperiod • sleep movements Fig. 26.15 Examples of sleep movements in prayer plants and morning glories. Fig. 26.13 Coiling response is an example of thigmotropism.

  5. photoperiodism • responses caused by changes in day-length • controlled by the pigment phytochrome • acts as a photoreceptor • best example is flowering • short-day vs. long-day vs. day-neutral plants Fig. 26.5 Graph of circadian rhythms in morning glories. The influence of photoperiod on flowering in long-day and short-day plants.

  6. Plant Defenses • like animals, plants have defenses against disease • bacterial, viral, and fungal infections • much of their defense is based on genetics • chemical attacks against pathogens • often localized in more vulnerable areas • phytoalexins, alkaloids, glycosides, etc. • plants also protect themselves from herbivores • structural defenses • spines, thorns, hair layers, tough bark, etc. • chemical defenses • toxins, inedible substances, sticky substances, etc. Fig. 26.19 Plant fungal infection Fig. 26.19 Examples of plant herbivores

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