Plant Maturation and Hormones

• Hormones act as growth regulators in plants.
• Auxin and Apical Dominance

  • Apical dominance: main stem dominance
  • Apical meristem produces auxin, which travels to tissues below preventing lateral growth
  • Auxin transport is polar/unidirectional
  • Down stem from shoots to roots via parenchyma cells (in ground & vascular tissues)
  • Removal of apical meristem or cessation of auxin causes lateral buds to grow
  • Lateral branches sprout & take over for the main shoot
• Role of Auxin

  • Auxin produced by seeds promotes fruit development
  • Involved in cell elongation and apical dominance
  • Promotes differentiation of xylem and phloem
  • Help to define long axis of body (phototropism and gravitropism responses)
  • First plant hormone isolated and characterized
  • Produced in shoot apical meristems and young leaves
• Cytokinins

  • Promote cell division in the presence of auxin
  • Promote chloroplast development and break lateral bud dormancy
  • Delay senescence (aging)
  • Produced in root apical meristems and many other tissues
• Gibberellins

  • Promote stem growth via both cell elongation and division
  • Promote seed germination
  • Produced in apical meristems, immature seeds, and anthers (pollen-producing organs)
• Abscisic Acid (ABA)

  • Inhibits bud growth and seed germination
  • Induces closure of stomata in response to water stress
  • Acts as a stress hormone analogous to cortisol in humans
  • Produced in almost all cells
• Ethylene

  • Exists in gas form
  • Involved in fruit ripening
  • Induces senescence of fruits, flowers, and leaves
  • Produced in all organs when plants are under stress
• Brassinosteroids

  • Promote cell elongation in stems and leaves
  • Structurally related to steroid hormones in animals
  • Produced in almost all tissues