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

The effect of the embryo axis on the activity of the glyoxysomal enzyme 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 activity and protein levels in cell-free extracts of endosperms from germinated seeds. In contrast, RNA slot and dot blot analyses revealed that the removal of the embryo axis did not affect the level of catalase transcripts in the endosperm. When cell-free extracts of isolated endosperms were subjected to non-denaturing isoelectric focusing and stained for catalase activity, at least 11 isoelectric isoforms were detected. The activity of these isoforms increased coordinately in endosperm cell-free extracts from germinated seeds. Significantly, the presence of the embryo axis was required to attain maximum activity of all isoforms observed. Further, the data presented in this paper show that following seed imbibition, the embryo axis alters the rate of synthesis of a number of endospermic proteins, in addition to catalase.