| At present, the studies of genetic improvement in rice are facing with two difficult problems in techniques, i. e. how to use hybrid vigor effectively and how to fix hybrid vigor via modern biotechnology. Previous research have been confirmed that polyploid rice possesses great potential value and it may be the most important germplasm in improving rice yield. In the present study, autotetraploid rice IR36-4X was treated with ion implantation technique by nitrogen ion beams and a polyembryonic seedling mutant (named as the IR36-Shuang) was identified in M2 generation. Stabilized polyembryonic seedling mutant line was obtained after several generations screening according to the screen method of descent line. The characteristics of the mutant has been studied in this paper. The development process of female gametophyte and male gametophyte of the IR36-Shuang was observed by using a Laser Scanning Confocal Microscopy technique. The results are as follows.1. The tissue culture system of autotetraploid rice with polyembryonic seedling has been founded in order to screen and improve the characteristics of the mutant. The rate and quality of forming calli lay on the culture medium and the contenting of the hormone. In differentiation culture medium, various relative hormone proportion and microelement Cu contents plays very important role in guiding plant regeneration . A material with high setting percentage was obtained in the regenesis plantes of autotetraploidrice with polyembryonic seedling.2.The frequencies of the twin-embryo seedling in the different germination temperatures was studied in order to identify the two-embryo seedling expressing characteristics. The results showed that autotetraploid rice might be effectively improved by ion beam bio-technique and the new germplasm with the hereditable twin-embryo seedling in subsequent generation had been obtained. The rate of twin-embryo seedlings showed obviously specificity in different lines and in the special temperature. At 30°C, The frequencies of the twin-embryo seedling of ASDOR05-01 and ASD0R05-02 were respectively 6. 8% and 2. 5%. The frequency of the twin-embryo seedling might be increase 32. 4%-36. 0% by husking the seed hull. The location of seedling in polyembryonic rice IR36-Shuang could be differentiated into 2 types, uncomplete twin seedlings and complete twin seedlings. There were 2 types in uncomplete twin seedlings, which were twin seedlings with single plumule axis and single radicle and twin seedlings with single radicle and twin plumule axis. The complete twin seedlings also included 2 types: normal twin seedlings and abnormal twin seedlings. In IR36-Shuang, the rate of twin seedlings with single radicle and twin plumule axis was higher than other types.3. The development process of female gametophyte and male gametophyte of the IR36-Shuang was observed by using a Laser Scanning Confocal Microscopy technique in order to study the characteristics of the male and female gametophyte in the mutants. The rate of abnormal male gametophyte in the IR36-Shuang was significantly higher than that in the primary parent IR36-4X. The frequency of abortive pollen in the mature pollens was 47.3%. The rates of typical, spherical and stained abortive were respectively 3. 8%,5.4% and 38.1%. Some abnormal division had been observed at the meiosis stage of microspore mother cell, for example, chromosome pairing abnormally, aberrant dyad formation or not synchronous dyad division, which might be the causes of the pollen abortion during later development. Most pollen abortion occurred at late bicellular pollen stage or early tricellular stage. The rate of abnormal embryo sacs in the IR36-Shuang, which is 34. 7%, was significantly higher than that in the primary parent IR36-4X, 24.5%. Multi-egg-cell egg apparatusa and double sets of embryo sacs appeared in IR36-Shuang, which might be developed into polyembryo in the plant. |
