Studies on the Development of Endosperm in Rice : XlL . Deve1oplIlent of the protein - forlring plastids

Abstract

Morphology and development of proteoplast or protein-forming plastid in rice endosperm tissue were studied electron microscopically. Proteoplast deposition commences at the 6 th or 7 th day from anthesis. The proteoplasts were found to be abundunt in the peripheral part of the endosperm, and their number decreased with decreasing distance from the center. Proteoplast has an outer membrane which is composed of two or three, or partially more layer of thin lamella, and it encloses a protein body of almost round shape. Protein bodies in the young stage of development are almost l-1.5 μ in diameter, and those in the mature cell are of 3- 4 μ. A few electron-denes areas are present in the periphery of the protein body. The internal structure of protein body in the young stage (less than 1 μ in diameter) is uniform in electron density. However, protein bodies in the middle stage (1-2μ in diameter) and in the mature (2-3μ) have two or more concentric zonal structure which consists of electron-dense and -thin zones arrayed alternatively. The respective zones have a width of almost 0.3 μ or more. The greater magnification of the protein body usually appears to have a number of minute granules. They show exceedingly high electron density, and are of diameter approximately 200Å. They are superior in number in the electron-dense zone than in the electron-thin zone. In some proteoplasts, an additional protein body is formed within the enclosure of outer membrane by the tinle when it enters the middle stage. Many of these proteoplastst talce on an amoeba-like form and some of them show the constricted forms. These findings may suggest that the proteoplast has, to some extent, the self-propagation nature.