Gibberellins

Biology: Cambridge International A Level, topic 15.2.3

Gibberellins have a role in seed germination and stem elongation.

Seeds are initially dormant (inactive).
When a seed begins to absorb water, gibberellin synthesis is stimulated.
Gibberellins promote seed germination by stimulating amylase synthesis.
Synthesising amylase enables the digestion of the starch in the endosperm of the seed, so the developing plant can access energy stored inside.
In wheat and barley seeds, the endosperm acts as starch storage.
Amylase breaks down starch into glucose. Glucose is then respired to produced ATP.

Gibberellins play a role in determining how tall or short a plant is.
Of particular importance is the Le/le gene.
The dominant Le allele codes for a key enzyme in the gibberellin synthesis pathway.
Gibberellins stimulate mitosis and cell elongation. Plants containing the Le allele grow tall.
The recessive le allele codes for a non-functional version of the enzyme. So, the resulting plants cannot produce gibberellins
So, homozygous recessive plants grow short.

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