Phytochrome control of cellulase activity in Datura ferox L. seeds and its relationship with germination

The influence of phytochrome on endosperm softening and cellulase activity was studied on light-stimulated Datura ferox seeds. Endosperm softening preceded the earliest signs of radicle protrusion, and there was good correlation between the % of seeds with soft endosperm at 48 h after R and germination at 96 h after R. Cellulase activity was stimulated by R and the increase in activity preceded, by more than 24 h, radicle protrusion and endosperm softening. The effect of R was reversed by FR, but, by delaying the irradiation with FR until cellulase activity had increased significantly, it was observed that removing Pfr did more than just stop any further increase, the level of cellulase activity decreased in about 24 h close to the dark controls. Cellulase activity was decreased by a FR irradiation even when more than 60% germination had escaped from reversion. These results indicate that phytochrome influence on cellulase is not an indirect consequence of the stimulus of germination and that the continuous presence of Pfr is required for the cellulase activity to remain high. The possibility that cellulase and other degrading enzymes may be part of the mechanism of light-induced germination is discussed.