Studies on White-Belly Rice Kernel : IV. Opaque rice endosperm viewed with a scanning electron microscope

Abstract

These studies in series were devoted to clarify the characteristics of the white belly kernel which had an opaque part at the ventral portion of its endosperm. In this experiment, white belly kernels were cut transversely with a razor blade and scanning electronic photographs were taken. The experimental materials used were Norin-8, Kinmaze, Sekai-1, Gohyakumangoku (white core rice) and Sinthurumochi (glutinous rice) of Japonica type variety and Keikyakusen and Kouketuzu (glutinous rice) of Indica type variety. The following results were obtained. 1. The translucent parts of endosperm tissue of white belly kernels were easily pervious to light, but the opaque parts of endosperm tissue of these kernels were difficult to transmit light (fig. 3, 6). The permeability of light in the individual endosperm cell varied from opaque parts to translucent parts (fig. 4, 8). 2. The compound starch granules in translucent parts of white belly kernel endosperm were polygonal in shape and tightly packed with no air spaces among them (fig. 12), whereas those in opaque part of this endosperm were round in shape and loosely packed with many intergranular air spaces (fig. 10, 13, 15, 23). 3. The compound starch granules, which located the outerside of opaque parts, were easily broken into many single starch granules by the mechanical stress (fig. 15-16). 4. The opaque parts of white core, milky white, and opaque kernels had round in shape, loosely packed compound starch granules resembled with those of white belly kernels (fig. 19-22). 5. The glutinous rice had micropores on the inside surface of the single starch granules and hollows on the outer surface of compound granules, which were absent in non-glutinous rice starch granules (fig. 25-27). 6. The endosperm cells in 5-day old kernels had uniform round compound starch granules which were loosely filled with many air spaces (fig. 28-29). The endosperm cells in 16-day old kernels were packed by compound starch granules which were varied in shape and size (fig. 30-32). In more developing kernels, the compound starch granules were tightly packed in the endosperm cell and no air space was observed among the granules. Then, the endosperm tissue became translucence ( fig. 33). 7. The starch granules of endosperm had two types, i. e., one was the large compound starch granule which was composed of many single starch granules and another was the small compound starch granules which were composed of several single starch granules. Among the compound starch granules, the globular protein body were embedded (fig. 37). 8. From these results, because of the loose structure and the high proportion of inter-granular air spaces, the opaqueness of endosperm tissue would be caused by light scattering.