化学药剂诱导玉米孤雌生殖植株的细胞遗传学研究

对化学药剂诱导玉米孤雌生殖获得的植株的染色体组成及其稳定性进行了研究。试验用2％二甲基亚砜(DMSO)+0.1％秋水仙碱;40％ppm马来酰胼(MH)+0.1％秋水仙碱;40ppm MH+2％ DMSO三种处理,共获得130粒孤雌生殖种子。本文对孤雌生殖种子的植株及后代进行了细胞遗传学分析、讨论。试验分析了145株孤雌生殖植株和对照植株的根尖细胞,和其中的88株的花粉母细胞。有半数以上植株的根尖细胞为混倍体,但除1株外,其余的混倍体植株的花粉母细胞均为二倍体。这一异常植株的花粉母细胞仍为混倍体,其子代中有二倍体和各种非整倍体植株。这一结果表明,用这种方法不仅能获得二倍体纯系,而且还可以获得非整倍体。     

Spontaneous and induced activation of rat oocytes

Ovulated rat oocytes undergo spontaneous activation during in vitro culture. After extrusion of the second polar body, they do not enter interphase but are arrested again in next metaphase-like stage (M III arrest). The present study demonstrates that puromycin and chloral hydrate can trigger transition to interphase of metaphase II and spontaneously (incompletely) activated rat oocytes. The response of oocytes to these activators depends on their stage at the time of application of a stimulus. Metaphase II oocytes enter interphase at 86.8% when treated with puromycin and in 28.7% after chloral hydrate activation. Oocytes activated with chloral hydrate at the time of spontaneously induced anaphase II enter interphase at 64.8%, but after reaching the stage of telophase II their capability to shift to interphase is again low (28.8%). Finally, M III oocytes cannot be forced to enter interphase by either chloral hydrate or puromycin treatment. This study shows that resumption of the second meiotic division and transition to interphase--the two processes that normally occur in succession as a response to oocyte activatin--can be experimentally separated.     

New data on the cytology of parthenogenetic weevils (Coleoptera,Curculionidae)

Parthenogenesis and, in particular, polyploidy are rare in animals. A number of cases, known among weevils, represent apomictic parthenogenesis-a reproductive mode in which eggs undergo one maturation division, the chromosomes divide equationally, and no reduction takes place. Among parthenogenetic weevils there are two diploids, 48 triploids, 18 tetraploids, six pentaploids, three hexaploids and one decaploid. Eight examined parthenogenetic species are triploids with 33 chromosomes of different morphology, confirming that triploidy is the most common level of ploidy in weevils. The karyotypes are heterogeneous with the presence of meta-, submeta-, subtelo- and acrocentric chromosomes. The C-banding method showed that only two species possess a large amount of heterochromatin visible as a band around the centromere during mitotic metaphase. This agrees with observations that weevils are characterized by a small amount of heterochromatin, undetectable in metaphase plates after C-banding. In three species an atypical course of apomictic oogenesis occurs with stages similar to meiosis, in which chromosomes form bivalents and multivalent clusters. This association of chromosomes probably represents the remnants of meiosis, although these events have nothing to do with recombination. The results support the hypothesis that the evolution of apomictic parthenogenesis in weevils has proceeded through a stage of automixis.     

Ultrastructural Observations on Parthenogenesis and Antipodal Apogamy of Allium tuberosum Roxb

Alliurn tuberosum Roxb is a species characterized by spontaneous parthenogenesis and antipodal apogamy. This paper deals with the ultrastructural changes during these processes. Before pollination, the mature egg cell contained abundant mitochondria with well developed cristae, spherical or ellipsoidal plastids and some polyribosomes, which suggested a relatively high metabolic activity. After fertilization, in zygotes the mitochondria changed to irregular shape and their cristae degenerated, the plastids elongated or became cup-shaped, the polyribosomes decreased and the free ribosomes increased in number. Some unfertilized egg ceils, two days after anthesis, showed similar ultrastructural changes as those taking place in zygote, which. seemed to be a sign of triggering to parthenogensis. In Allium tuberosum Roxb, the three antipodai cells bore a close resemblance to the egg apparatus: Among them two antipodal cells were similar to the synergids with a filiform apparatus-like structure and plentiful organelles at their chalazal end. The other was an egg-like antipodal cell which could undergo similar ultrastructural changes as those happened in zygote, leading to divide into apogamic proembryos two days after anthesis. The problems of parthenogenesis and antipodal apogamy in Allium tuberosum Roxb is diicussed in view of ultrastructural features of the egg and egg-like antipodal cell.     

Vertical stratification of oribatid (Acari: Oribatida) communities in relation to their morphological and life-history traits and tree structures in a subtropical forest in Japan

To clarify the effect of tree structure on the diversity of oribatid mites (Acari: Oribatida), we collected a total of 16,325 oribatids in 181 morphospecies from the leaves, branches, and trunk bark of trees and from the forest-floor soil and litter in a subtropical forest, Okinawa, Japan, and tested three predictions: (1) moisture stress in arboreal habitats would lead to larger body size (not supported); (2) morphological traits related to gripping a surface (number and size of claws) would be more developed in arboreal species (supported); and (3) advantages in colonization (no cost for searching mates and doubled population growth) would favor parthenogenesis in the arboreal oribatid communities (not supported). We observed vertical stratification among the five habitats in terms of mite density, species diversity, and species composition, but found no difference in the body length of oribatid species between the arboreal and forest-floor habitats. However, (homo-)tridactylous species predominated in the arboreal habitat, suggesting that this claw morphology facilitates adherence to and movement on arboreal substrates. Sexual species were common in the arboreal oribatid communities, whereas about half of the dominant species collected from the forest floor were likely to be parthenogenetic. It is unclear how these different reproductive systems may be advantageous for oribatid mites in arboreal and forest-floor habitats. Nevertheless, the structural complexity provided by trees appears to enhance and maintain the diversity of oribatid communities through vertical stratification in this subtropical forest.     

Influence of spatial structure on the maintenance of sexual reproduction

We include spatial extension into a model for the maintenance of sexual reproduction introduced recently. The model is based on a broad spectrum of resources, which regrow slowly. Other key features of the model are that sexual reproduction sets in when resources become scarce and that only a few genotypes can coexist locally. The extension of the model to several patches in space is done in two different ways. Model A is based on central egg deposition and allows migration of juveniles into all patches. Model B has a one-dimensional array of patches with migration only between neighboring patches. The main findings are that wide dispersal favors asexuals, while for slower migration there is a wide range of parameter values for which sexually reproducing species always win against asexuals. These results are conform with major patterns for the distribution of parthenogenesis in animals and plants, i.e. the prevalence of parthenogenetic reproduction in minute species, which are easily dispersed by physical forces, such as protists and small metazoans including e.g. bdelloid rotifers, tardigrades and nematodes.     

标记辅助选择在水稻改良中的应用前景

标记辅助选择在水稻改良中的应用前景郑康乐（中国水稻研究所,杭州３１０００６）黄宁（国际水稻研究所,马尼拉１０９９）ＯｕｔｌｏｏｋｏｎｔｈｅＡｐｐｌｉｃａｔｉｏｎｏｆＭａｒｋｅｒ－ａｓｉｓｔｅｄＳｅｌｅｃｔｉｏｎｉｎＲｉｃｅＩｍｐｒｏｖｅｍｅｎｔＺｈｅ...     

Fertilized eggs obtained from transplantation of frozen ovaries and parthenogenesis in combination with artificial insemination of frozen semen of the silkworm,Bombyx mori

A reliable method is reported for the long-term preservation of ovaries and spermatozoa of the silkworm (Bombyx mori). Three studies are presented. In the first, ovaries were removed from larvae at either 3rd, 4th, or 5th instar, cryopreserved, and stored in liquid nitrogen. Thawed ovaries were transplanted to surgically castrated female larvae at the same or a different developmental stage. The highest percentage of recipient females producing eggs resulted into either 3rd or 4th instar larvae (respectively, 22.1 and 8.7%). Similarly, the highest levels of other measurements of successful cryopreservation and transplanted ovary, and number of eggs laid, occurred with the same combination of donor and recipient developmental stages. Other combinations of ovary/recipient developmental stages yielded lower results. In the second experiment, semen was collected from male moths, cryopreserved, and then thawed semen was diluted with trypsin solution and artificially inseminated into females obtained from the best conditions of first experiment. A small percentage of inseminated moths laid eggs (8-10.3%) compared to that of controls (100%). In addition, the fertility of eggs from experimental moths was lower than that of control females (respectively, 40.3-88% and 97.5%). In the third experiment, eggs were surgically removed from ovarian tubules of moth following transplantation of thawed ovaries and subjected to parthenogenetic activation and artificial hatching. As expected, all resulting moths were female and, following natural mating or artificial insemination with thawed semen, yielded normal offspring at high rates.     

Differentiation diversity of mouse parthenogenetic embryonic stem cells in chimeric mice

Recent studies have illustrated multiple differentiation potentials of embryonic stem cells (ESCs), derived from parthenogenetic embryos, to various kinds of cells (all three embryonic germ layers). However, differentiation diversity of the parthenogenetic ESCs (PgESCs) in vivo remains to be elucidated. In the present study, we established mouse PgESC-lines and observed their contribution diversity in vivo by producing chimeric mice using embryos possessing single nucleotide polymorphisms of mitochondrial DNA (mtDNA) as hosts. Based on southern blot analysis using specific probes to detect the SNPs on mtDNA, PgESC-derived mtDNA were contained in many organs such as brain, lung, and heart of the chimeric mouse. We concluded that PgESCs contributed to various internal organs in vivo, and that they were also stably maintained in adult animals.