Isolated aleurone cells and protoplasts of cereal grains are particularly useful model system for studying of gibberellin signaling. Up to now, the identity of the receptor protein is unknown, but its activity in cereal aleurone has been localized to the plasma membrane. The gibberellin-signaling pathways identified in aleurone cells involve heterotrimeric G proteins, 1,4,5-inositol triphosphate, Ca2+, calmodulin, cGMP, cytosolic pH, protein phosphorylation, and transcription factors.