ABSTRACT
Barley aleurone offers a model system to study protein secretion in plants. Aleurone layers produce and secrete a range of enzymes in response to gibberellic acid (GA3). Most are hydrolases with an obvious role in endosperm mobilization and for some both synthesis and secretion are totally under (GA3) control. Since the synthesis of alpha-amylase and its release from the aleurone are totally under (GA3) control and all enzyme produced is destined for secretion, localisation of alpha-amylase in any organelle is direct evidence for involvement of that organelle in the secretory pathway. The discovery of alpha-amylase in the rough endoplasmic reticulum is consistent with biochemical evidence which indicates that alpha-amylase carries a signal sequence and is sequestered in microsomes. Gold particles should occur only where alpha-amylase protein with reactive antigenic sites is present. In the cell walls gold particles were very precisely localised over the digested regions, indicating that alpha-amylase, like other hydrolases is specifically released via digested wall channels.
