Effects of Nitrogen Application on the Development and Accumulation of Protein Bodies in Developing Rice Seed

Abstract

We examined the nature of protein bodies affected by nitrogen application in developing rice endosperm using scanning and transmission electron microscopes. Protein body type II, Pb-II, was observed at the first week after heading independent of nitrogen application, whereas protein body type I, Pb-I, was not observed in either the low nitrogen or non-fertilized group. However, in the high nitrogen group, Pb-I was also observed at 1 week after heading. Pb-I was formed by enlargement of endoplasmic reticulum cisternae, but Pb-II had a close relationship with the Golgi apparatus and was accumulated in the envelope-like vacuole. The smallest protein body, Pb-III, about 0.6-0.8 μm in diameter, appeared at 2 weeks after heading, and the amounts of this protein body increased substantially at 3 weeks after heading. This protein body also originated from endoplasmic reticulum cisternae. Pb-I was observed only in cytoplasm, but, Pb-II appeared in both the endoplasmic reticulum and envelope-like vacuole. The amount of protein bodies in the rice endosperm cell varied with the cultivar and amount of nitrogen applied. In cv. Koshihikari (Japonica), the application of much nitrogen increased the amount of protein bodies not only in the subaleurone, but even in the fifth layer from the aleurone layer. However, in cv. Belle patna (Indica), the application of much nitrogen increased the amount of protein bodies up to the sixth ayer of aleurone layer, and caused the accumulation of a few protein bodies even in the central part of endosperm. It was concluded that storage protein transported by Golgi vesicles and rough endoplasmic reticulum (RER) plays an important role in the accumulation of reserve substances in rice seed. Development of mitochondria and RER was enhanced by the application of nitrogen.