植物多倍体的形成及其二倍化机制

大约70%的开花植物在进化史上都经历过多倍化的过程,多倍体植物通常具有较强的可塑性,容易形成新物种。而新形成的多倍体往往不能稳定存在,其基因组需要再经历一次二倍化的过程,从而在基因水平上和细胞学水平上更接近二倍体。对多倍体二倍化的机制和相关研究的未来发展情况进行了探讨。     

Increasing the genetic uniformity of bighead carp [Aristichthys nobilis (Richardson)] by means of spontaneous diploidization of gynogenetically activated eggs

Three groups of gynogenetic diploid bighead carp were successfully obtained by means of artificial gynogenesis. The activation rates of gynogenesis varied from 75.9% to 98.8%, and the frequency of spontaneous diploidization was around 0.4%. Over 2000 normally gynogenetic diploid fry were obtained in three gynogenetic groups. The haploid karyotype consisted of nine metacentric, 12 submetacentric, three subtelocentric chromosomes and 45 arms. The chromosome number was 48 from gynogenetic diploid. The results showed that the genetic material of offspring was maternal. The aneuploid hybrid embryos of bighead carp and Xingguo red common carp with chromosome numbers ranging from 28 to 73 did not survive post hatch, likely the result of incompatibility between the nucleus and the cytoplasm of two parents. Sixty RAPD primers from three groups were used for total DNA amplification of gynogenetic offspring, maternal and ‘paternal’ fish. A total of 451 bands were amplified from three kinds of samples above. From maternal bighead carp, 256 bands were amplified; however, there were 251 shared bands between maternal and gynogenetic bighead carp. From artificial gynogenetic offspring, two ‘paternal’ DNA segments without an expression function were found. An UPGMA tree showed that gynogenetic offspring were closely clustered and the genetic identity among them was very high (0.956).     

Diploidization in Haploid Tissue Cultures of Sorghum

Conditions for the effective experimental regulation of ploidy level in regenerants from callus cultures derived from young, undifferentiated leaves and panicles of haploid sorghum were established. Diploidization depended on the ontogenetic age of the explant and the 2,4-D concentration in the medium. With a low 2,4-D concentration (0.5 mg/1) and segments of young panicles (< 35 mm long) the cultures produced only haploid regenerants. Diploid plants were formed from cultures derived from more mature panicles ( 35 mm long) and young leaves (15–65 mm long). Under a high 2,4-D concentration (2.5 mg/1) diploid plants were regenerated from cultures derived from young panicles (less than 35 mm) except the most young ones (5–15 mm). The majority of the diploid regenerants contained mutations, mainly affecting male fertility and plant height.     

甘蓝型油菜小孢子单倍体二倍化技术的研究

采用6种方法系统研究甘蓝型油菜（Brassica napus)品系（种）及杂种的小孢子再生苗单倍体染色体加倍技术。结果表明，单倍体苗接种含70－80mg/L秋水仙碱的培养基处理4－5d，植株染色体加倍率50％以上；单倍体小苗移栽前用1－2g/L秋水仙碱液浸泡处理3－6h，加倍率50％以上，由这些方法产生的加倍植株大多是可育花和不育花共生的嵌合体，每株产生的种子很少。分离的小孢子在含10－50mg/L秋水仙三的NLN培养基中处理48h后，接种无秋水仙碱NLN培养基诱导胚状体，再生植株加倍率80％以上，全株的花均能自交结籽，嵌合植株很少。     

玉米单倍体自然二倍化研究

本研究以玉米杂交种郑单958诱导产生的玉米单倍体群体为材料,利用流式细胞仪对单倍体自然条件下的二倍化现象进行了观察。结果表明,在自然条件下,体细胞加倍与生殖细胞加倍并不显著相关,雌雄穗加倍存在差异,并且雌穗自然加倍率较高。雄穗可育单倍体植株的体细胞基本上处于单倍状态(1C),少数体细胞中存在单倍体与二倍体细胞的倍性嵌合现象,并检测到了1%~2%的非整倍体(1.5C)现象。体细胞二倍化有随雄穗育性水平升高而增加的趋势。     

Effective Diploidization of Microspore-Derived Haploids of Rape (Brassica napus L.) by In Vitro Colchicine Treatment

A technique for the in vitro colchicine treatment of microspore-derived haploids of rape (Brassica napus L.) is presented. This allows effective and time-saving chromosome doubling. The most effective method consists of an application of 50 mg/1 colchicine in a liquid B5 medium to the rooted micro-spore-derived plantlets for 4–8 days. By this treatment more than 50 % of the plants developed at least diploid sectors. A change of medium after some days may even increase this diploidization rate.     

Genetic characterization of spontaneous diploid androgenetic wheat and triticale plants

The homozygosity of spontaneous hexaploid plants derived from anther culture was evaluated in wheat and triticale by means of 18 and 22 microsatellite markers, respectively. Most of the spontaneous hexaploid plants were homozygous for all the loci tested and had chromosomes recombining for parental alleles. Only 12% of the spontaneous hexaploid wheat plants, 11% of the artificially doubled wheat plants and 4.4% of the spontaneous hexaploid triticale plants were heterozygous at one to three of the loci studied. This showed that spontaneous hexaploid plants mostly came from normal haploid cells, obtained after meiosis, that underwent spontaneous chromosome doubling. However, first or second division restitution, producing unreduced gametes, cannot be completely excluded to explain the origin of the spontaneous hexaploid plants. Cytomixis, involving only one chromosome, or development of aneuploid trisomic gametes, followed by chromosome doubling for the spontaneous hexaploid plants, or transposition events could also explain some of the results obtained.     

胡萝卜小孢子胚状体和愈伤组织的诱导

选用胡萝卜7个常规品种、10个自交系、16个F1代杂交种和6个F2代材料研究基因型、植物生长调节剂、AgNO3以及低温预处理（4 ℃）对花药培养的影响。在参试的39份材料中有6份材料产生小孢子胚状体,其中50071号材料出胚率最高,达到3.89%,有30份材料产生小孢子愈伤组织,其中600Q6号材料出愈率达到36.70%。在B5培养基上添加2,4-D和NAA组合中,选用的4份参试材料均产生小孢子愈伤组织,其中50071和70Q67号材料产生胚状体,而添加6-BA和NAA组合中均未产生胚状体和愈伤组织。培养基中添加AgNO3对部分材料的出胚率有一定促进作用,50071和70Q67号材料在8 mg · L-1 AgNO3下出胚率分别达到10.00%和2.00%。低温预处理对部分材料的胚状体及小孢子愈伤组织形成有一定作用,50069号材料经4 ℃ 1 d预处理出胚率达1%,预处理2 d和3 d出愈率均达到11.25%,70Q67号材料在3 d预处理后出胚率达到4.00%。经细胞学鉴定,在121株由胚状体产生的再生植株中93.39%为二倍体,说明胡萝卜花药培养过程中易发生自然加倍。     

Spontaneous diploidization of the maternal chromosome set in Nile tilapia (Oreochromis niloticus L.) eggs

Spontaneous diploidization of the maternal chromosome set (SDM) in Oreochromis niloticus is described here for the first time. The SDM phenomenon was observed in progeny of only one XY neofemale out of 11 such neofemales from which eggs had been fertilized with UV‐irradiated sperm: this treatment produced only the expected haploid embryos from the other females. SDM progeny were produced from three different batches of eggs from this female. No significant differences in survival at different stages of embryonic development were observed between the SDM and the diploid control group. The maternal inheritance of SDM progeny was verified using multilocus DNA fingerprinting. Only diploid karyotypes were observed in these fish and diploid control groups. In both the SDM and control groups, sex ratios were significantly skewed towards males (93.3% and 65.0% males respectively). The actual mechanism of SDM in eggs from this particular female remains unknown.