甘蓝型油菜胚柄多胚突变体(Brassica napus twn-119)的细胞胚胎学研究

多胚突变体B.napus twn-119是从甘蓝型油菜品种中油119中发现的.经过连续套袋自交选育,目前已使多胚频率提高到34%.所获得的多胚种子萌发后,92%的种子中萌发出各自独立的双苗,6%种子中萌发出独立三苗,2%的种子中得到3个以上独立苗.偶尔可观察到生长的幼苗具有三片、四片子叶、幼苗的茎发生部分结合及子叶上具轴状附属物等异常现象.对多胚突变体的胚胎学研究表明,由顶细胞发育而来的初生胚体正常发育成胚,部分胚柄细胞转变成为具有强烈分裂能力的细胞而不是进入程序性死亡.这些特殊的胚柄细胞具有胚胎发生能力,胚柄中可以观察到多个球形原胚形成,多个原胚由宿存的胚柄细胞连接成一串.如果两原胚之间连接的胚柄细胞很少或没有,两个胚体在发育过程中会发生部分融合.幼苗根尖染色体数目的检查也证明多胚幼苗都具有正常油菜的染色体数目(2n=38).

Cytoembryological and morphological characterization of a polyembryonic mutant Brassica napus twn-119

Polyembryony,or multiple embryos within the same seedcoat,occurs spontaneously in many plant species including Brassica napus.However,the origins of the polyembryos in B.napus are unclear.In this report,we characterized a B.napus mutant,twn-119,which shows high frequency of viable twin,triplet and sometimes more embryos within the same seedcoat.The frequency of polyembryony observed was 34?%.92?% of the polyembryonic seeds germinated into two independent seedlings,6?% germinated into three independent seedlings,2?% germinated into more than three independent seedlings.We found that the supernumerary embryos originated at an early stage of embryo development through the transformation of suspensor cells.In this mutant the primary embryo proper(EP) developed normally while some of the suspensor cells were transformed into meristematic cells instead of going into programmed cell death(PCD).These meristematic cells were of embryogenic ability and developed into one,two,three or more embryos in one suspensor so that globular proembryos developed in tandem within the seed and were connected by segments of the suspensor.Additionally,a number of polyembryonic seedlings exhibited abnormal morphology with three or four cotyledons and occasionally,axis-like analogues were attached to the seedling apex.All root tips from polyembryonic seedlings had a diploid chromosome complement(2n=38).