Gibberellin and germination, illustrated in a seed of barley (Hordeum vulgare).

aleurone endosperm embryo A Absorbed water causes cells of a barley embryo to release gibberellin, which diffuses through the seed into the aleurone layer of the endosperm. gibberellin B Gibberellin triggers cells of the aleurone layer to express the gene for amylase. This enzyme diffuses into the starch-packed middle of the endosperm. / C The amylase hydrolyzes starch into sugar monomers, which diffuse into the embryo and are used in aerobic respiration. Energy released by the reactions of aerobic respiration ‘ fuels meristem cell divisions in the embryo.