Proteinase activities in resting and germinating seeds of Scots pine, Pinus sylvestris [pine proteinases 1 and 2, pepstatin-sensitive proteinase, seedlings]

Resting seeds of Scots pine contained a moderate amount of acid proteinase activity, about 90% of which was inhibited by pepstatin A and about 10% by p-hydroxymercuribenzoate. In gel chromatography on Sephacryl S-200 the protinase activity showed a complex elution pattern with poorly separated peaks at positions corresponding to mol. wts. 100,000 and 30,000 and several shoulders. The results suggested that pine proteinases I and II, which are the main proteinases in the endosperms of germinating seeds (Salmia 1981: Physiol. Plant. 51: 253-258), were not present in the resting seeds. Seedling extracts showed a low level of acid proteinase activity, which separated into several peaks in chromatography on Sephacryl S-200. As none of the peaks had the catalytic properties of proteinase I or II, it seems that these endospermal enzymes are also lacking in the seedling tissues. In the endosperms of germinating seeds the activity of the pepstatin-sensitive acid proteinase(s) remained at a constant level throughout the period of reserve protein mobilization (lasting up to the stage when the length of dark-grown seedlings was 60 mm). Proteinases I and II were absent from resting seeds, showed a small increase up to the 20-mm stage, and then increased rapidly up to the 60-mm stage. Resting embryos contained relatively higher acid proteinase activity than resting endosperms and again about 90% of it was inhibited by pepstatin A and about 10% by p-hydroxymercuribenzoate. During germination the former activity decreased, the latter activity remained at approximately the same level, and the activity of the other acid proteinases increased continuously with the growth of the seedling. It is concluded that the pepstatin-sensitive proteinase(s), which is not affected by endogenous proteinase inhibitors, plays a central role in the initiation of reserve protein mobilization in both the embryo and the endosperm. Proteinases I and II, on the other hand, seem to account for the greater part of reserve protein breakdown in the main protein storage tissue, the endosperm.