Protease inhibitors in germinating Echinocloa (Echinocloa fruneutacea) seeds: changes in protease inhibitory activities during germination

Antitryptic activity in echinocloa seedlings disappeared completely by the seventh day during germination, whereas antichymotryptic activity remained at a level comparable with that of the dormant seeds. Purified trypsin/chymotrypsin inhibitor from dormant echinocloa seeds was used as a substrate to study the nature of proteases arising during germination. A carboxyl protease localized in the root portion of the seedlings was responsible for the inactivation of the seed inhibitor with reference to the loss of antitryptic activity, and a thiol protease diminished its antichymotryptic activity in vitro. The shoot portion of the seedlings contained both antichymotryptic activity and antitryptic activity. The root extract preferentially destroyed the antitryptic activity of the shoot extract. The data suggest that the trypsin/chymotrypsin inhibitor of echinocloa seed is inactivated and mobilized during plant growth and that a new inhibitor appears in the shoot portion of the plant during growth.