| Improvement of rice quality is one of the major research subjects in recent years. Rice with intermediate amylose content that cook tender but not sticky is generally preferred, although consumers' preferences in the habit of eating rice vary in various areas. However, currently, most of rice varieties especially the indica rice varieties, have too high unylose content, resulting in poor quality. Thus, breeding indica varieties or hybrid parents with intermediate or lower amylose content becomes one of the most important objects in rice genetic breeding.The amylose in rice endosperm is synthesized by granule-bound starch synthase (GBSS) that is a product of the waxy gene. In present paper, the dependability of "PCR-yicc I " molecular marker of rice waxy gene was verified and correspondingly the molecular marker assisted selection was used to improve the starch quality of rice; On the other hand, Agrobacterium-mediated transformation was applied in introducing the antisense waxy gene into the indica maintainer lines in order to reduce the amylose content of receptor varieties properly. By the two paths, the feasibility and practical effects of improving rice starch quality by biotechnology were probed into. The major results are as follows:1. The "PCR-Acc I "molecular marker of rice waxy gene has been use to determine whether the first nucleotide of splice donor site of waxy intron 1 is G or T in 106 rice varieties. Simultaneously, the amylose content in mature seeds of these varieties was determined by using chemical methods. The results show that the amylose content in the varieties with base G at position +1 of waxy intron is always high, while that in all of the varieties with base T at the corresponding position is intermediate or low. Thus, the molecular marker can be used to predict the amylose content of rice varieties.2. Analysis of the F2 populations derived from two crosses between indica rice varieties with high and intermediate amylose (Gang 46BXDxianglB and Zhenshan97B DxianglB) shows that whether the first nucleotide is G or T in waxy intron 1 are co-separated with high or low amylose content, respectively, in mature seeds. The ratio of the genotype TT: GT: GG is 1: 2: 1 in the F2 generations of Zhenshan97B X Dxiang 1B.3. Gang 46B is a maintainer line with high combining ability but high amylose content. The starch quality of Gang 46B was improved by introgressing the waxy gene from Dxiang IB, a good quality indica maintainer line with intermediate amylose content. The PCR-AccI molecular marker was applied in the series to select individuals with TT or GT genotype in the process of cross and backcross breeding. The relation between amylose content of some individuals from F5, BC1F4, BC1F5, BC2F3, BC2F4, BC3F2 generations and their waxy genotype (TT, GT or GG) were studied. The results show the PCR-Acc I molecular marker of rice waxy gene can be effectively applied in selecting the target plants with good quality waxy gene to improve the starch quality of rice in cross and backcross breeding. In this study we have gotten five target plants that have intermediate amylose content and the same genotype TT as DxianglB, the donor parent of good quality waxy gene from the BC3F2 generation by the PCR-Acc I molecular assisted selection.4. The antisense waxy gene was introduced into D62B and D702B, two indica hybrids maintainer lines with high amylose content, by Agrobacterium-mediated transformation. 11 HygBr plants were produced, of which 9 and 2 tranformants were gotten in D62B and D702B respectively. Simultaneously, some factors influencing the transformation frequency are preliminarily discussed.
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