Temporal and spatial pattern of the biochemical activation of the endosperm during and following imbibition of tomato seeds

Electron microscopic observations of the endosperm of tomato (Lycopersicon esculentum Mill.) seeds revealed that changes in the cell wall structures along with the vacuolation of protein bodies occurred in the micropylar portion of the endosperm prior to germination. No changes were detected at that time in the rest of the endosperm. Endo‐β‐mannanase activity was restricted to the micropylar region of the endosperm prior to germination. Cell wall digestion by this pregerminative mannanase seemed to be associated with the changes in cell wall structures occurring in the micropylar region prior to germination. The protein content in the micropylar part of the endosperm began to decrease shortly after imbibition and attained about 40% of the initial level by the time of radicle protrusion (38 h after imbibition). On the other hand, only slight changes in the content were detected in the lateral endosperm during the same time; the protein content in the lateral endosperm decreased only after germination started. In conformity with the results on protein contents, proteolytic activity began to develop first in the micropylar portion prior to germination, and then in the lateral portion after germination. Thus, the timing of the biochemical activation of the endosperm after imbibition differed between the micropylar and the lateral region. Some qualitative differences in patterns of polypeptides synthesized in vivo were detected, as analyzed by pulse‐labeling and fluorography, between the micropylar and the lateral portions of the endosperm of seeds imbibed for 25 h. This suggests that processes of the biochemical activation of the endosperm may be qualitatively, as well as quantitatively, different depending on the regions of the endosperm.