EFFECT OF THE EMBRYO AXIS ON CATALASE IN THE ENDOSPERM OF GERMINATINGCASTOR BEAN-SEEDS

The effect of the embryo axis on the activity of the glyoxysomal enzym e catalase (EC 1.11.1.6) in the endosperm of germinating castor bean ( Ricinus communis L. cv. Hale) seeds was examined. The presence of the embryo axis was required for maximum levels of catalase enzyme activit y and protein levels in cell-free extracts of endosperms from germinat ed seeds. In contrast, RNA slot and dot blot analyses revealed that th e removal of the embryo axis did not affect the level of catalase tran scripts in the endosperm. When cell-free extracts of isolated endosper ms were subjected to non-denaturing isoelectric focusing and stained f or catalase activity, at least 11 isoelectric isoforms were detected. The activity of these isoforms increased coordinately in endosperm cel l-free extracts from germinated seeds. Significantly, the presence of the embryo axis was required to attain maximum activity of all isoform s observed. Further, the data presented in this paper show that follow ing seed imbibition, the embryo axis alters the rate of synthesis of a number of endospermic proteins, in addition to catalase.