Hormonal signalling in cereal aleurone

The cereal aleurone is an excellent model system for hormonal signalling in plants. When treated with gibberellins (GAs), cereal aleurone layers and aleurone protoplasts initiate signalling cascades that result in the synthesis and secretion of hydrolytic enzymes, most notably a-amylases. Abscisic acid (ABA) antagonizes the effects of GA and stimulates the production of ABA-up-regulated proteins. Receptors for GA and ABA have been localized to the aleurone cell PM, and evidence suggests that another ABA receptor functions within the cytoplasm. Cytosolic and membrane-bound second messengers have been identified and signal transduction pathways are beginning to be understood. Transacting factors that regulate the transcription of hormonally induced genes have been cloned and bring us closer to linking cytosolic signals to changes in gene expression. In this review, recent data pertaining to hormonal signalling in cereal aleurone are summarized, Relationships between signalling and effector molecules are discussed, and models for hormone-induced signalling pathways are proposed.