米の胚乳発達に関する組織形態学的研究 : 第10報 肛乳澱粉粒の発達について

抄録

Starch deposition in endosperm cell starts from the 4th day after anthesis. At the outset, several numbers of very small starch granula ('granulum' used herein, id defined to be an unit of a compound granule, and 'granule' is defined to be the whole starch content consisting of an amyloplast) deposit almost simultaneously in each proplastid. Cytoplasm of the endosperm cell is in the very rudimental state at this stage, and the proplastids are full of variations in shape, and most of them are irregular oval-shaped ones, but some have amoeba-like shape. The proplastids multiply by means of their own constriction or segmentation division during the subsequent one or two days. Therefore, it can be said that almost all the proplastids are already endowed with several (or at least one) starch granula in the structure from the outset of their formation. With the growth of proplastid in size, number and size of granula become increased also. It is considered appropriate that the developing proplastid should be known as 'amyloplast' after the time when the self-multiplication has ceased and the granula deposition in the plastid stroma has been closed. After this stage, amyloplast takes the oval shape. Starch granulum takes the polyhedral shape in the stroma from the outset of its formation, and it may not be right to say that the space limitation results in change in the granulum shape from spherical to polyhedral one. Although 'shell structure' or 'daily growth rings' is not found in rice starch granulum, the ununiformity in. the stratified structure of the granulum section suggests that there is a fair possibility that the growth of the granulum is accelerated in the manner in which new starch molecules are added to the outside of 'the existing granulum. Amyloplast is enveloped loosely in the plastid membrane of double structure. The membrane has many creases and seems to keep some partial contacts with endoplasmic reticulum. It is also noteworthy that a golgi body (dictiozome) can be found almost always at the near side of amyloplast. Such structure is considered to have some relationship to the introduction of reserve substances into amyloplast and the synthesis of starch in the amyloplast. By the 15th day after anthesis, the starch granules that started to develop from the 4th day reach about 20μ each in major axis, thus almost completing morphologically. In the mature amyloplast, about 50 to 80 granula are included. From the above evidence, it is clear that rice starch granule has the characteristic of compound granule from the start of its development, and undoubtedly it consists of a single amyloplast. Such results support the BUTTROSE'S opinion, but offer opposition to the views on the part of AIMI and MURAKAMI who insisted upon that compound starch granule consisted of several amyloplasts.