What are hormones and what do they do?

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Contributed by: Dutchmaster

What are hormones?
" Hormones are organic molecules which can have influence on the physiology of plants and animals". Plants produce hormones themselves naturally, but when selected hormones are added in low concentrations, they can have a positive influence on the physiology of plants.

1. Transport is not necessarily needed to let hormones work.
2. The effect of hormones depends on concentration and sensitivity of the plants.

The best understood hormones are:
# Auxine
# Gibberellic acid
# Cytokinine
# Ethylene
# Abscisine

The most important areas in a plant where they are produced are young leaves, young seeds, pre-flowering buds and the stem.

  • Auxine has a positive influence on cell stretching, cambium activity, and bud formation.
  • Auxine is transported to the lower parts of the plant by chlorophyll cells (parenchymcells).
  • Auxin transport goes very slowly @ 1cm/hour.
  • Transporting Auxine costs a lot of energy.
  • Inactivation of Auxine happens when it binds with sugars and/or oxidation.

    When you top your plant, the roots of your plant will grow a lot slower. When you add extra auxine, the roots will grow again and form new roots. This is why auxine is a major ingredient in root stimulators. Auxine works better in conjunction with Cytokinine.

    Mostly produced in young leaves, but roots also produce it. It is transported from the roots to the leaves and branches.

    When Gibberellic acid is added to the roots, it will suppress the formation of lateral roots, but the cell stretching of the other parts of the plant will speed up and be more excessive.

    Gibberellic acid can germinate seeds faster, and a higher % of female seeds will be produced (feminized seeds). Be careful though: too much Giberellic acid is not healthy.

    Concentration of Cytokinene is highest in young plant material (leaves and roots).

    Activates cell stretching, triggers flowering and germination. Slows the aging of plants, and protects membranes against oxidation.

    When the concentration of Cytokinine and Auxine is high, it will develop buds, stems and leaves. If the concentration is low, complete plants will form. When there is less Cytokinine than auxine, roots will develop. High Cytokine concentrations will transport products of assimilation.

  • Inactivation of this hormone happens when it binds with sugars or because of oxidation.
  • The "glucosides" of Cytokinine could be a buffering and transportation form for the plant.

    Formed within the plant, but is also produced by fungus and bacteria. Biological activity within the planting medium can regulate amounts of this hormone, and have an influence on your plants.

  • Transport happens because of the intercellular spaces.
  • Inactivation caused by oxidation.
  • Ethylene can also be given to the atmosphere as a gas

    Normally, Ethylene production will slow down cell stretching and thicken the roots and stem (germination)

    Too much Ethylene can deform and even kill your plants. For instance, when the roots are in too much water, the production of Ethylene will almost stop, but so is the ability to gas it off to the atmosphere. If this happens, leaves will turn chlorotic (eventually leaf death), stems will stretch, and there will be an increased susceptibility to attack by diseases.

  • Slows down cell dividing, cell stretching and bud formation.
  • Abscisine acid is an antagonist of Gibberellic acid, Auxine and Cytokinine.
  • Slows down the growing and flowering of plants.
  • Produced in older leaves and chlorophyll.

    Final note:
    Do not start experimenting with plain hormones unless you are very sure of what you are doing!
  •   Last modified: 16:55 - Feb 23, 2003 

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