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Plant Control Systems and Defenses



Plant control systems and defenses allow plants to grow and respond to their environments. Plants have systems to control their life processes, such as germination from a seed, growth rate, sexual reproduction, and production of seeds and fruit. The controls for these processes are hormones, and there are five primary types or groups of hormone that dominate plant control: auxin, abscisic acid, cytokinins, ethylene, and gibberellins. Growth and structural development, however, are not the only areas in which hormones play a role. Hormones also signal dangers, such as possible damage or disease. Although plants may appear to be defenseless, they actually have a number of defense systems that protect them from predators and diseases.

At A Glance

  • Plant hormones control growth, development, and reproduction.
  • Plant hormones signal plants to undergo changes such as seed germination or winter dormancy.
  • Auxin influences plant cell growth and cell expansion.
  • Abscisic acid is a plant's stress hormone, synthesized when the plant faces environmental stressors.
  • Cytokinins affect cell division and the formation of new plant organs.
  • Gibberellins encourage plant growth.
  • Ethylene is a gaseous hormone that stimulates ripening and aging.
  • Although they are anchored to soil, plants may exhibit spontaneous or induced movement.
  • Tropisms are plants' positive and negative responses to stimuli.
  • Day and night influence a plant's circadian rhythms.
  • Plant defenses include defenses against pathogens, structural defenses, and chemical defenses.
  • Plants defend against pathogens by way of waxy leaves, hormones, and external and internal structures.
  • Plant structural defenses include thorns, prickles, spines, and trichomes.
  • Chemical defenses emitted by plants include bad odors to repel predators, pleasant odors to attract animals that prey on the plant's predators, and toxins that cause direct harm to predators.