Localization of Carboxypeptidase I in Germinating Barley Grain 1

Activity measurements and Northem blot hybridizations were used to study the temporal and spatial expression of carboxypeptidase I in germinating grains of barley (Hordeum vulgare L. cv Himalaya). In the resting grain no carboxypeptidase I activity was found in the aleurone layer, scutellum, or starchy endosperm. During germination high levels of enzyme activity appeared in the scutellum and in the starchy endosperm but only low activity was found in the aleurone layer. No mRNA for carboxypeptidase I was observed in the resting grain. By day 1 of germination the mRNA appeared in the scutellum where its level remained high for several days. In contrast, little mRNA was observed in the aleurone layer. These results indicate that the scutellum plays an important role in the production of carboxypeptidase I in germinating barley grain. or to secretion from the surrounding living tissues, the aleurone layer, or the scutellum. The aim of the present study is to determine whether carboxypeptidase I is synthesized during germination and if so-whether the synthesis takes place in the scutellum or in the aleurone layer. In addition to enzyme activity, mRNA for this enzyme was also localized. MATERIALS AND METHODS