Studies Of Variation And Inheritance Of Seed Protein Content In Rice (Oryza Sativa L.)

Rice (Oryza sativa L.), one of the most important crops, is a very good and relatively cheap source of energy and protein. It is rich in starch and proteins, and the seed storage proteins are regarded as one of the high-quality plant proteins due to be easily digested and assimilated. However, rice contains the lowest protein level among cereal, thus, it is important to breed rice varieties with high proteins content and improved nutritional quality to meet the demands and purposes of consumer. Since the abundance of germplasms and wide variaton of proteins content in rice, it is of vital significancy to investigate and study the content, composition, inheritance of seed storage proteins, with the aim to provide some theoretical and technical supports for the improvement of rice protein quality in present study.We attempt to do some research on measurements, variation, composition, inheritance of rice seed storage proteins among lots of rice varieties. The main results were as followings. 1. Using collected 483 rice grain samples, the crude protein contents in brown and milled rice were carefully determined by either Near infrared spectroscopy (NIRS) or Kjeldahl nitrogen determination method. The data demonstrated that it was of fine stability and veracity by NIRS technique to measure the crude protein content. The results of correlation and regression analyses showed that there was a significant linear correlationship between the crude protein contents determined by both methods. Thus, the reliability and methods were discussed to forecast the real protein content in different rice types via the values determined by NIRS technique.2. The crude protein contents in 351 varieties were measured by NIRS method and their distribution and classification were analyzed. The results showed that, in general, the crude protein content in indica rice was higher than that in japonica rice. According to the criterion of classifying of protein contents, most of rice genotypes fell into the group with intermediate protein content. And there were very small number of varieties with either high or low protein contents, especially with very high level in japonica rice.3. The distribution of protein content in different parts of brown rice was carefully studied in three rice varieties with different quality and grain shape. The analysis of relationship between protein content and degree of milling indicated that the protein content of the grains decreased from outer to inner fractions, and the protein content in core endosperm fractions was only about half of that in bran layers, but the downtrend varied among different varieties.4. Several parents with different seed protein contents were used to produce different F₁ crosses, and subsequently F₂ populations, and the protein contents were measured and compared in brown rice of F_1-2 seeds from F₁ plant, F_2-3 seeds from F₂ individuals and their parents. The results of genetic analyses revealed that there were limited hybrids showing heterosis over higher-parent, meaning with high protein content than both parents. And the protein content in most of F_1-2 seeds was lower than that of the mean of two parents (middle parent, MP), indicating that low protein content might be dominant among most combinations. The distribution of protein contents in F_2-3 seeds among F₂ population was identified to be normal, suggesting that the characteristics of seed protein content might be controlled by multiple genes. Furthermore, there was a high broad heritability of seed protein content in F_2-3 seeds of F₂ population.5. The expression pattern of the OsAS gene encoding asparagine synthetase was studied via Northern blotting analysis, and the possible relationship between nitrogen assimilation and the synthesis of seed proteins was analyzed. The results suggested that the expression level of OsAS gene varied with different tissues and development periods, it preferred a highest expression level in spikelets, but very low in leaf sheath and blade. During grain developing, the OsAS transcript in spikelets increased firstly, and then declined rapidly. Moveover, the data indicated that the expression level of OsAS gene in the blade of 17 rice varieties exhibiting no significant correlation with the seed protein content in mature seeds, but a correlation seemed existing between them among different varieties of the same indica or japonica subspecies.