Protein Body Formation and Immunocytochemical Localization of Globulins and Glutelins in Developing Rice (Oryza sativa L.) Embryos

Abstract

Rice (Oryza sativa L.) is one of the world's most important cereal crops. It plays a major role in human nutrition and its storage proteins have been thoroughly studied. Most of the research has concentrated on endosperm storage proteins. Embryo storage proteins have received only limited attention. Experiments were conducted to compare immunological relationships between the predominant endosperm globulins and those of the embryo. We examined the cellular and biochemical aspects of embryo storage proteins with light microscopy and transmission electron microscopy at three developmental stages. At 2 d after fertilization (DAF), embryos were globular in shape and were made up of actively dividing cells. These cells contained prominent vacuoles without any protein accumulation. At 6 DAF, the embryos had achieved distinct polarity, with cells at the basal region accumulating increasing amounts of starch and lipid. Moreover, these cells contained distinct types of vacuoles, most of which contained numerous dark‐staining protein inclusions. At 16 DAF, the embryo cells were filled with lipid bodies and contained prominent vacuoles that had accumulated substantial amounts of protein deposits. Antibodies raised against purified rice endosperm α‐globulin and against glutelin cross reacted with embryo proteins in Western blot analysis. However, the most abundant storage proteins of rice embryos did not react with these antibodies. Electron microscope immunocytochemistry revealed that proteins similar to α‐globulins and glutelins were deposited within the vacuoles. As in endosperm tissue, the glutelins and the α‐globulins were deposited within the same protein bodies. However, the embryo protein bodies were morphologically distinct from endosperm protein bodies. This study demonstrates the occurrence and localization of proteins similar to endosperm glutelins and globulins within the protein bodies of rice embryos.