| Rice is the main grain crop.The storage protein in rice seed accounts for about 10% of the total rice weight and plays an important role in the growth and development of rice as a source of carbon,nitrogen,and sulfur.Glutelins and prolamins account for approximately 60%-75% and18%-25% of the total seed proteins of rice,respectively,and play a decisive role in the quality of rice proteins.Prolamin polypeptides are synthesized in the rough endoplasmic reticulum,and accumulated into the globular protein body(PB-I)derived from ER;Glutelins are synthesized in the rough endoplasmic reticulum with 57 kDa precursor polypeptides,transferred to the protein storage vacuoles(PSV)in the form of vesicles passing or bypassing the Golgi apparatus,processed into the mature of40 kDa acidic and 20 kDa basic components in PSV,and eventually accumulated to form the irregular vacuolar PB(PB-II)in the developing endosperm cells of rice.The four 57 H mutations that resulted in the highly increased deposition of 57 kDa glutelin precursor and the remarkably decreased deposition of the mature glutelins have been involved in the post-translational accumulation of storage proteins,however,no genic mutations concerning storage protein synthesis have not been reported.In our laboratory,the three novel mutants(GPH series),which increased 57 kDa polypeptides and not decreased 40 kDa and 20 kDa polypeptides,recently have been obtained by screening 410 rice germplasm resources.In order to explore functional information for novel57 H mutations affecting generating of storage proteins,phenotypes and sub-cellular accumulation states of of storage proteins in the GPH1 and GPH3 mutants with the representative traits were analyzed in this study.Analysis of characters for endosperm storage proteins showed that GPH1 and GPH3 highly increased 57 kDa glutelin precursors but not decrease the mture glutenlins,and that GPH1 had character of 13 kDa prolaminlack in addition to the glutelin precursor increase.Electron-microscopic observation based on the electronic staining showed the existence of the wild-type PBs in the endosperm cells of normal cultivar(Liaoyan 6),the existence of the complex ER structure and the ER-derived complex-PB formed by binding of spheroids in GPH1 endosperm cells,and the existence of the complex PB structure composed of a spheroid and micro-particles coated on its surface in GPH3 endosperm cells.Electron-microscopic observation based on the immuno-gold labeling of stored protein antibodies showed that the complex PB structure was formed by combination of glutelin precursor spheroid and prolamin spheroid in GPH1,and that the complex PB structure was composed of prolamin spheroid and glutelin precursor particles on its surface in GPH3.Confocal microscopic observation based on the immuno-fluorescence labeling of the ER marker protein(BiP)antibody showed that BiP were distributed as ribbon and cluster states in Liaoyan 6 and GPH1,respectively.These results indicate that GPH1 mutation result in alteration of ER form and affect synthesis and accumulation of storage proteins,and that GPH3 mutation may also is associated with the synthesis of storage proteins.The results in this study are important to the understanding of genetic mechanism regulating synthesis of rice storage proteins and the breeding research for rice quality of rice proteins. |
