CIE A Level Biology复习笔记15.2.3 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 (eg. 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 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

The role of gibberellin in the germination of a barley seed