REGULATION OF DE-N-GLYCOSYLATION ENZYMES IN GERMINATING RADISH SEEDS

The activities of the de-N-glycosylation enzymes endo-N-acetyl-beta-D- glucosaminidase (ENGase; EC 3.2.1.96) and peptide-N4-(N-acetyl-beta-D- glucosaminyl) asparagine amidase (PNGase; EC 3.5.1.52) were monitored during germination and postgerminative development in radish (Raphanus sativus L. cv Flamboyant). The ENGase activity was detected only duri ng postgermination, whereas the PNGase activity was present at high le vels in both stages. When germination was inhibited with abscisic acid or cycloheximide, PNGase activity was detected at a basic level and E NGase activity was not detected at all. PNGase is present as an active protein in dry seeds and is apparently synthesized during seed format ion. Conversely, the absence of ENCase in dry seeds suggests that its activity is dependent on the protein synthesis that occurs during and after germination. Treatment with gibberellic acid confirmed the produ ction of both de-N-glycosylation enzymes after germination, and demons trated a temporal delay between the production of the two enzymes duri ng this period. Our results suggest that the two de-N-glycosylation en zymes are differentially regulated during plant development.