Degradation of Amyloplast Envelope and Discussion on the Concept of Compound Starch Granule in Rice Endosperm

The development of starch granule, degradation of amyloplast envelope and morphology of compound starch granule were observed with the transmission electron microscopy and scanning electron microscopy. Many starch granules formed and developed in one amyloplast. The morphology of starch granules changed from spheroid to ellipsoid with development. Starch granules became polyhedral when they contacted to each other in amyloplast. The amyloplast envelope began to degrade after amyloplast was full of starch granules. Degraded membrane fragments surrounded cytoplasmic matrix to form ring membrane structure. Well developed starch granules were polyhedral with compact arrangement in amyloplast, and these starch granules kept the outline of amyloplast after amyloplast envelope degraded. Mature grain with well developed starch granules showed transparence where the fracture surface was suggested to be between endosperm cells. Poorly developed starch granules were round or elliptic with loose arrangement in amyloplast, and these starch granules did not keep the outline of amyloplast after amyloplast envelope degraded. Mature grain with poorly developed starch granules showed chalkiness where the fracture surface was suggested to be through endosperm cells. In addition, the concept of compound starch granules was discussed.