of aleurone and cause the cells to develop as starchy endosperm cells instead of aleurone cells. This causes the seed to lack an aleurone layer. This mutation is caused by the insertion of a Mu transposon into the dek1 gene, causing it to function incorrectly. However, this transposon may sometimes remove itself from the gene, restoring the function of dek1. Experiments in this area have helped demonstrate that the cues that determine aleurone positioning are still present in the later stages of development, and the aleurone cells still respond to these cues. Similar to the dek1 mutation, genes with a mutation in the cr4 gene also cause a switch in the fate of aleurone cells. The cr4 gene codes for a receptor kinase and so is involved in signal transduction pathways involving the fate of aleurone cells. Plants with a mutated cr4 gene are shorter than normal and produce crinkled leaves. In addition, several hormones influence the development of the aleurone layer, including auxin, cytokinin, abscisic acid (ABA), and gibberellin (GA). Auxin and cytokinin play a role in the earlier stages of aleurone development. The maturation of aleurone is promoted by ABA while germination is promoted by GA. Aleurone function The aleurone layer performs a variety of functions to help maintain proper development of the seed. One example of this is maintaining a low pH in the apoplast. In cereals, the aleurone layer releases organic and phosphoric acids in order to keep the pH of the endosperm between a pH of 3.5 and 4. In barley, the aleurone layer also releases nitrite into the starchy endosperm and apoplast under anaerobic conditions. In addition, although the function is unclear, a certain class of hemoglobins is present in the outer layer of living cells including the aleurone tissue in barley and rice seeds. During seed germination, the plant embryo produces the hormone gibberellin which triggers the aleurone cells to release α-amylase for the hydrolysis of starch, proteases, and storage proteins into the endosperm. Evidence that G-proteins play a role in the gibberellin signaling events has been obtained. The breakdown of the starchy endosperm supplies sugars to drive the growth of roots and the acrospire. This release of amylase is considered to be the most important and sole function of the aleurone layer. This effect is inhibited by the plant hormone abscisic acid, which keeps the seed dormant. After completing this function, the