Introduction.

Molecular structure of Gibberellin (GA).

Gibberellins, a group of plant growth hormones, are synthesised in high concentrations in developing seeds. They are also synthesised in varying amounts in other parts of the plant eg apical shoot buds and root tips. One particular and important function of gibberellins is there role in stimulating hydrolysis and transport of stored macromolecules, to the developing embryo. Following water uptake, in the initiation of germination, gibberellin diffuses to a specialised layer of cells, called the aleurone layer. In response to gibberellin, these cells which are rich in protein, produce and release enzymes that hydrolyse lipids, starch and proteins in the  endosperm. The starch, lipids and proteins are converted to sugars, fatty acids and amino acids, respectively. The embryo will use these for growth and development.

In this experiment carried out on germinating barley seeds, the results showed that the release of gibberellin from the embryo, triggers the synthesis of the hydrolytic enzyme alpha-amylase, which digests starch in the endosperm. It is hypothesised that gibberellins, in this instance atleast, turn on the genes encoding for alpha-amylase.