1989 年 54 巻 3 号 p. 409-417
The mesophyll cell section of an unimbibed primary leaf appeared with a large number of protein bodies, a few mitochondria and 2 to 3 proplastids. The proplastids were identified as membrane bound structures with irregular shape and within the stroma appearance of one or two electron dense bodies and small portions of membrane (prothylakoids). The membranebound mitochondria can be distinguished from the proplastids by their small more regular shape and their electron transparent appearence at the centre. Cristae can be identified in a few of them. A close association between proplastids and mitochondria was noted.
The starch grains were first detected in the proplastids from 12h imbibed leaves. A peak number of starch grains per plastid section was noted after 36h, after which this value fell.
The protein bodies in the cell section were reduced in number accompanied by the development of starch grains in the proplastid section after 24h of imbibition. Proplastids became spherical and the most part of the stroma was covered with a number of starch grains in the mesophyll cells after 36h of imbibition. The most characteristic feature of this stage was the occurrence of plastid as well as cell division. During the next 2days the number of starch grains per plastid section fell although the number of grains per cell section remained fairly constant. The increase in the number of plastid sections per cell section indicated that plastid divisions occurred more rapidly than cell divisions during the first 4 days of dark growth.
Therefore, this report identifies the proplastid in the dry embryonic leaf and the commencement of plastid division accompained by cell division after 36 h of imbibition. The development of etioplast from proplastid is characterized by the increase in number of starch grains in the stroma and the reduction of the number of protein bodies in the cytoplasm.