Formation of Protein Bodies in the Starchy Endosperm of Rice (Oryza sativa L.): A Re-investigation*

The mechanism of protein body formation in the starchy endosperm is described for two rice varieties, one of normal protein content and the other high in protein. Three types of protein bodies were found in both rices. While each protein body type was deposited differently, the mechanism of formation for the same type in the two varieties was analogous. First secreted was the large spherical protein body. It was deposited within rough endoplasmic reticulum, had a dense centre and a concentric ring appearance, and was bounded by a single membrane. The second protein body to form was crystalline, was found in vacuoles, and was secreted via the Golgi apparatus. The third type, the small spherical protein body, was secreted late in development, was deposited in vesicular rough endoplasmic reticulum, and lacked dense centres and concentric rings. The high protein rice had a thicker sub-aleurone layer than the normal protein rice.