Localization of ?-amylase isozymes within the endomembrane system of barley aleurone

Abstract

The localization of α-amylase (EC 3.2.1.1) in barley (Hordeum vulgare L. cv Himalaya) aleurone protoplasts was studied using electron microscope immunocytochemistry. Antibodies were raised against total barley α-amylase, i.e., α-amylase containing both highisoelectric point (high-pI) and low-pI isoforms, as well as against purified high- and low-pI isoforms. All antibodies localized α-amylase to the endoplasmic reticulum (ER) and Golgi apparatus (GApp) of the aleurone cell, and various controls showed that the labeling was specific for α-amylase. Labeling of protein bodies and spherosomes, which are the most abundant organelles in this cell, was very low. There was no evidence that α-amylase isoforms were differentially distributed within different compartments of the endomembrane system. Rather, both high- and low-pI isoforms showed the same pattern of distribution in ER and in the cis, medial, and transregions of the GApp. We conclude that in the Himalaya cultivar of barley, all isoforms of α-amylase are transported to the plasma membrane via the GApp.