The Role of Gibberellin in Germination of Barley (Cambridge (CIE) A Level Biology): Revision Note

The role of gibberellin in germination of barley

• Gibberellins are a type of plant growth regulator involved in controlling seed germination and stem elongation

• When a barley seed is shed from the parent plant, it is in a state of dormancy (contains very little water and is metabolically inactive)

• This allows the seed to survive harsh conditions until the conditions are right for successful germination (e.g. the seed can survive a cold winter until temperatures rise again in spring)

• The barley seed contains:

  • An embryo—will grow into the new plant when the seed germinates

  • An endosperm—a starch-containing energy store surrounding the embryo

  • An aleurone layer—a protein-rich layer on the outer edge of the endosperm

• When the conditions are right, the barley seed starts to absorb water to begin the process of germination

• This stimulates the embryo to produce gibberellins

• Gibberellin molecules diffuse into the aleurone layer and stimulate the cells there to synthesise the enzyme amylase

  • In barley seeds, it has been shown that gibberellin does this by regulating genes involved in the synthesis of amylase, causing an increase in the transcription of mRNA coding for amylase

• The amylase hydrolyses starch molecules in the endosperm, producing soluble maltose molecules

• The maltose is converted to glucose and transported to the embryo

• This glucose can be respired by the embryo, providing the embryo with the energy needed for it to grow