| The process of pollination, fertilization and embryo development of 4x × 2x and 2x× 4x in head cabbage was observed by the ways of fluorescence microscopy and paraffin section . Then the characters of quality, growth and development, meiosis behavior and gamates transmitting rate of the triploid plants obtained by 4x×2x were studied ,the methods of saving young embryo collapse and improving the seed setting were researched in this paper.The results were showed as follows:1 The process of pollination and fertilization was normal in 4x× 2x and 2x × 4x which is similar to 2x and 4x .The cause of embryo collapse in both combinations lied in cutting off supply of nutrition necessary to embryo development due to endosperm degeneration and inner integument cells dying off in early embryo development phase.But the time of the embryo collapse was different in the both combinations, in 4x×2x the embryo collapse generally took place at heart-shaped or late heart-shaped embryo stage and finally formed small seeds,while in 2x ×4x,the embryos collapsed at small globe-shaped embryo stage and could not formed seeds.2 The pod setting in both 4x ×2x and 2x ×4x were very high and without marked difference ,but their fecundities were different remarkablely,some small seeds and a few of big seeds were obtained in 4x×2x which the former included triploid,hyperploid and hypoploid ,the later were all tetraploid, but only a few big seeds were observed in 2x X 4x which were all tetraploid .3 The effect on accelerating young embryo development was based on kind, concentration and proportion of IAA and BA which were treated to swelling ovaries. It showed that the treatment of 200 ppmIAA +200ppmBA was most effective which the seed setting 3.87 times CK.4 About 50% of the isolated ovales with late heart-shaped embryo could accomplish afterripening and germinate into seedlings directly when cultivated in MS medium, while those with early stage embryo failed completely.5 The small seeds obtained in 4x ×2x could germinate in MS medium as well in wet filter paper, and the rates of germination and abnormal seedling were higher in the former than in the later.6 The triploid head cabbage showed the general characters of polyploid plant, such as,having stronger resistance to higher temperature, weight and some minion indexes of plant being higher, leaf type index becoming smaller than diploid plants. The anthesis was similar to tetraploid but later than diploid plants.7 The meiosis behavior of triploid head cabbage was much more complex than that of diploid.It showed as foilowsrat diakinesis,trivalent was major while divalent and univalent was minor.Some free monoverient chromosomes were observed at metaphase I , II. The separate types showed 9/18,10/17,11/16,12/15,13/14 whose rates were 0.77%, 3.87%, 8.76%, 31.19% and 48.45% respectively at anaphase I , of which the 10/17 was the most useful in selecting the trisomics.8 That abnomal meiosis behavior produced many microspores with unbalanced composing of chromosomes was the main cause of pollen collapse.9 Seed sets and rate of 2n+1 plants were 10.46% and 26.47% respectively in 3x X 2x while 0.83% and 72.7% respectively in 2xX3x. It showed that pollen could only transfer n+lgametes,whereas megaspore even could transfer n+2,n+3 gametes besides n+1 gamete.10 Diploid cabbage plants which could naturally produce unreduced 2n gamete were discovered for the first time.Similar to in Chinese cabbage .the cytological mechanism of unreduced 2n gamete formation in cabbage was mainly due to the abmormal orientation of spindles at metaphase II which led to formation of dyad and triad, dyads were the direct souce of 2n gamete in cabbage unlike Triads in Chinese cabbage.
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