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Introduction to Plant Hormones

Introduction to Plant Hormones. Bielke F2012. What are plant hormones?. Plants need a method of responding to their environment to cope with predation and abiotic stresses, such as drought. ( Abiotic = non-living )

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Introduction to Plant Hormones

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  1. Introduction to Plant Hormones Bielke F2012

  2. What are plant hormones? • Plants need a method of responding to their environment to cope with predation and abiotic stresses, such as drought. • (Abiotic = non-living) • Plants do not have a nervous system, so a major way in which they respond to the environment is by using plant hormones, often called plant “growth factors”.

  3. What are plant hormones? • Unlike animal hormones, plant growth factors are not made in specialized organs but in many tissues all over the plant. They may be used where they are made, or transported within the plant. They usually exert their influence by affecting growth.

  4. Effects of plant growth factors • Plant growth can be divided into three main types: • cell division • cell elongation / enlargement • cell differentiation (specialization). • These types of growth can all be controlled by plant growth factors

  5. Tropisms • A tropism is the movement of part of a plant in response to, and directed by, an external stimulus. The movement is by growth and is therefore slow. It is described as positive or negative depending on whether the growth is towards or away from the stimulus respectively.

  6. Tropisms

  7. Difficulties in Studying Growth Factors • The effects of a plant growth factor can depend on: • the concentration of the growth factor • the tissue being acted on (stems or roots) • the developmental stage of the plant • the species of plant • what other growth factors are present. Another growth factor can increase the effect of the growth factor being studied (synergism) or reduce it (antagonism) • Growth factors are only present in small amounts

  8. Types of Plant Growth Factors • Auxins promote cell elongation and phototropism • Gibberellins promote seed germination and growth of stems • Ethylene promotes fruit ripening and leaf fall

  9. Types of Growth Factors • Cytokinins promote cell division • ABA (abscissic acid) inhibits seed germination and closes stoma to conserve water when plant is under stress (as in during a drought)

  10. Which growth factor ? • Ethylene • Fruit ripening and leaf fall

  11. Which growth factor ? • Gibberellins • Seed germination and growth of stems

  12. Which growth factor ? • Auxin • Phototropism and cell elongation

  13. Which growth factor ? • Cytokinins • Promote cell division and growth

  14. Which growth factor ? • ABA • Seed germination inhibited • Stoma close under drought conditions to conserve water

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