Gibberellins and Seed Germination

The endosperm of a barley grain stores food mainly in the form of starch, which the embryo cannot use directly.
When the seed imbibes water, the embryo produces gibberellic acid (GA).
GA diffuses to the aleurone layer and induces it to synthesise and secrete hydrolytic enzymes, the most important being $\alpha$-amylase.
$\alpha$-amylase hydrolyses the starch of the endosperm into maltose and glucose.
These soluble sugars are absorbed by the scutellum and supplied to the growing embryo, so germination proceeds.
This is used in the malting of barley in the brewing industry.
So the enzyme that can stimulate the germination of barley seeds is $\alpha$-amylase.