Hormone intro & HW assignment



Abscisic acid





Discovery: In 1901, Dimitry Neljubow recognized ethylene as a plant regulator, but it wasn't until 1934 that R. Gane fully identified ethylene as the first gaseous plant produced hormone.

It is found in tissues of ripening fruits, nodes of stems, senescent leaves and flowers. Ethylene is produced by the degradation of methionine, an amino acid.


Ethylene has actually been used for centuries for its properties: both the Chinese and Egyptians used it for hastening the period of fruit ripening.

Effects of Ethylene:

  • Fruit Ripening -- Ethylene stimulates all these factors of fruit ripening:
    1. Breakdown of chlorophyll and synthesis of other pigments.
    2. Fruit softening by cellulase and pectinase cell wall breakdown.
    3. Formation of volatile compounds - attractants.
    4. Conversion of starches and acids to sugars.

    This "climacteric response" does not occur in all species however - it is true for apples, tomatoes and avocado but not for citrus, grapes or strawberries

  • Flowering -- Ethylene inhibits flowering in a lot of species, but promotes it only in few species. It also promotes senescence of flowering plants.
  • Abscission -- An increase in ethylene production causes the breakdown of the middle lamella and this results in abscission. It is also used to increase the efficiency of harvesting fruits, such as cherries and grapes.
  • Sex Expression -- The sex of flowers on monoecious plants (contain both male and female flowers) is determined by gibberellins and ethylene.
    1. Gibberellins -- Male flower
    2. Ethylene -- Female flower

    It is used to synchronize flowering in pineapple to get that perfect shape!

  • Stem Elongation -- Shaking increases ethylene production, which causes cells to grow long which cause cells to form short, thick stems.