Cytological Investigation On The Female Sterility Of A Dominant Genic Male-Sterile Line In Brassica Napus

Male-female gametophyte development, fusion and double fertilization are important marks of metagenesis in flowering plants. If some unusual happen in internal and external condition during the continuous development process of male gametophyte, male gametophyte would be sterile, and all the same in the female gametophyte. The female gametophyte is an essential structure for seeds formation in flowering plants. Female sterility can't be made up by healthy pollens, so need to avoid in agricultural production. In the study of sterility in dominant genic male-sterile Brassica napus, we found different degrees of phenomenon of female sterility expressed in male-sterile line Rs1046AB and derivative male-sterile lines FM195AB-1 and FM195AB-2. To overcome this negative trait, study the causes of female sterility of male-sterile line, the main results as follows:1. Different levels of female sterility in numbers of male-sterile lines, the average seed numbers is 5.5 per pod in original male-sterile line Rs1046A, the least is 1-2, the seed rates of both male-sterile lines has significant differences. The number of seed per pod of heterozygous male-sterile lines is significantly higher than homozygous.2. Female-sterile occurs only in sterile plants of dominant genic male-sterile lines, it isn't impacted by environmental, this phenomenon shows female-sterile and male sterile are linked closely, it's like that the dominant male gene expresses two different effects in development of female and male. Occurrence of female-sterile may be associated with the dosage effect of sterility genes.3. Stigmas of Brassica napus Rs1046AB and FM195AB have no obvious differences. Pollen grains are germinating soon after they locates in the stigma, pollen grains in the stigmas of Brassica napus Rs1046B are germinating normally 4h after artificial pollination, it indicated that abnormale pistil stigmas is not the cause of female-sterile. Pollen tubes elongate in stylar and gather nearby the ovules successfully in FM195AB, there is significant difference before pollen tubes enter the ovule in FM195AB:the morphology of pollen tubes is normal in fertile plants, it's just like irregular lines with arrow-shaped bright spot, lots of pollen tubes gather nearby the ovules, and enwrap ovules; but in sterile plants, the morphology of pollen tubes is abnormal, coiled serious, pollen tubes gather nearby the ovules successfully, but not enwrap.4. Analyze female gametophyte development of FM195AB before fertilization, we found five major types of abnormalities with different proportion in the mature embryo sac in FM195A.5. Comparing the development stage of embryo sac with the anther, we found the meiosis of the microsporocyte is abnormal, nor form tetrad. In the same period of the pistil, there is no formation of the functional megaspore, and in subsequent ovule development, there is no mononuclear embryo, thus speculate that meiosis is abnormal in ovules of sterile plants. In anther, exception occurs in the period of meiotic interphase. The above observation showed:abortion of anthers and ovules happened in the same period, both in meiosis, but in ovules, a few sac developed normally.Based on the above results, we speculate that the meiotic abnormalities leads to female-sterile. Abnormal ovule development could not form the normal functional sac, on the other hand could not guide the pollen tube extension and enter into the ovule. As the similarity of the abnormal development in anthers and ovules, suggesting dominant male sterile gene Ms causes the male and female sterility, it implied ms plays an important role in meiosis of the female gametophyte.