| China is the origin centre of Chinese cabbage-pak-choi (Brassica campestris L. ssp. chinensis Makino; syn. B, rapa L. ssp. chinensis) which is cultivated in a wide range of area and plays an important role in farming industry. Chinese cabbage-pak-choi is also a kind of crops of obvious heterosis, So much attention has been paid to the research on male sterility mechanism and its application in Chinese cabbage pak-choi. With the development of modern bio-techniques, the molecular biology shows large potentiality, which is taken advantage of explaining the molecular mechanism of male sterility. Studies of genes related to male sterility will provide a theoretical basis for elucidating the mechanism of male sterility and lead the way to application of heterosis by means of gene engineering. Constructing a cDNA library is the basis of studying on molecular biology, and is an effective mean of cloning specific genes, especially the high eukaryotes genes.'Aijiaohuang' A/B lines used in this study is a representative genie male sterility in Chinese cabbage-pak-choi, and it is also an optimal plant material in the research of male sterility mechanism. Studies were performed on morphology in the A-line and B-line. A cDNA library of floral bud was constructed and the partial characters of the library were identified. In order to validate the function of the cDNA library, primary screening was made. The following results were obtained:(1) Comparative analysis has been made between A-line and B-line of Chinese cabbage-pak-choi, such as the plant characters, fertility and structure of floral organs. The results of plant morphology indicated that there is nearly no distinct difference between sterile plants and fertile plants in the seedling stage, but in the bolting and flowering stage the growth vigor of sterile plants is stronger than that of fertile plants. There are distinct differences between sterile plants and fertile plants on the phenotype of their flowers. The filaments of sterile plants are short, and its anthers are small, shriveled, white and without pollen, but the pistils developed naturally and fertilized normally. The filaments of fertile plants developed naturally, and its anthers are plump and yellow. The results showed that the A-line and B-line of Chinese cabbage-pak-choi were reliable and stable with the ratio 1 : 1 of sterile plants to fertile plants, and the pollen of sterile plants was abortive thoroughly.(2) Total RNA extracted from B-line's floral bud was reverse transcripted into first strand cDNA using SMART?technique. The double strand cDNA which digested by Sfi I was ligated to Sfi A and Sfi B sites in the vector .TriplEx2. The partial characters of the library were analyzed: about 8 X 105 recombinants had been obtained after the mixture of ligation was packed in vitro and the host strain E. coli XLl-Blue was infected. And the titer of amplified cDNA library is about 3 X 107 pfu-mL-1. 50 clones were chosen randomly from the library, and the PCR products of cDNA inserts were tested by electrophoresis. The result showed that 70% of the fragments sizes were more than 500 bp and the average length of cDNA inserts was 760 bp. The recombinant rate of the library was about 87% by Blue/White Screening.(3) Probed with the gene fragments related to male sterility we obtained previously, phage in situ hybridization has been done, and the results showed that the hybridization signal is obvious and clear. This demonstrated that the cDNA library of Chinese cabbage-pak-choi floral bud had been constructed successfully, and it can be well employed to study the genes related to male sterility in future.
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