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1.
 Cytoplasmic determinants that specify the fate of endoderm, muscle and epidermis cells are known to be localized in specific areas of fertilized eggs of ascidians. The presence of such cytoplasmic determinants in unfertilized eggs was demonstrated in previous studies, but no information has yet been proved about their distribution. To investigate the distribution of cytoplasmic determinants in unfertilized eggs, we devised a method for distinguishing the polarity of unfertilized eggs using vital staining and we performed cytoplasmic-transfer experiments by fusing blastomeres and cytoplasmic fragments from various identified regions of unfertilized eggs. Cytoplasmic fragments, that contained cortical and subcortical material, from five different positions along the animal-vegetal axis were prepared, and they were fused with a4.2 (presumptive-epidermis) or A4.1 (non-epidermis) blastomeres. The ectopic development of endoderm, muscle and epidermis cells that was promoted by the transplanted cytoplasm was assessed by examining the expression of alkaline phosphatase (ALP), myosin and epidermis-specific antigen, respectively. Differentiation of endoderm and muscle was observed at higher frequencies as cytoplasmic fragments closer to the vegetal pole were transplanted. Conversely, formation of epidermis was observed at higher frequencies as cytoplasmic fragments closer to the animal pole were transplanted. The results suggest that, in cortical and subcortical regions of unfertilized ascidian eggs, endoderm and muscle determinants are widely distributed along a gradient, with maximum activity at the vegetal pole, whilst epidermis determinants are also distributed along a gradient but with maximum activity at the animal pole. Recieved: 10 June 1996 / Accepted: 12 September 1996  相似文献   
2.
Autonomous division of the endosperm was induced by in vitro culture of unpollinated ovaries or placenta-attached ovules in Helleborus niger, Lupinus luteus and Melandrium album. The induction frequencies for the three species were 50%, 10–20% and 0.1%, respectively. The endosperms contained up to 20 free nuclei; only a few ovules with 80–420 endosperm nuclei were found. Induction of autonomous division of the endosperm, which is unusual in amphimictic plants, was observed in three new species. No embryos appeared in the ovules. This suggests a developmental independence of the endosperm from the embryo in the culture of unpollinated ovaries or ovules.  相似文献   
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北京地区油松胚珠发育时期的确定   总被引:1,自引:0,他引:1  
采用显微观察法对北京地区不同发育时期的油松胚珠进行解剖结构观察,以确定北京地区油松胚珠的发育时期。结果表明,北京地区油松胚珠的发育历时13个月(从2003年4月~2004年5月),具体时期为:2003年4月12日为胚珠分化期,4月21日左右为大孢子母细胞时期,5月至8月为游离核时期,2003年8月至2004年2月为胚珠休眠期,2004年4月15日左右进入雌配子体细胞化时期,4月21日左右为颈卵器原始细胞活动期,5月8日左右为中央细胞分裂期,5月14日左右为成熟颈卵器时期。本研究结果中油松胚珠经历的发育阶段与前人的研究基本一致,但在时间上存在差异,而且北京地区比辽宁兴城地区油松胚珠发育时期平均提前了大约20~30 d。  相似文献   
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Current patterns of floral design in Pedicularis must have undergone an evolutionary process of interacting among components of floral traits, and then formed internal relationships among these traits. To detect such correlations, which may provide insight to understand flower evolution, 40 Pedicularis species representing all corolla types of the genus were studied. Results show that, interspecifically, pollen size correlates negatively with pollen number, but positively with pistil length. This suggests that plants evolve an optimal pollen size, which balances the advantages of large pollen size for gametophytic competition against the fecundity disadvantages of fewer pollen grains. In contrast to sex allocation theory, this study does not find a trade-off, but an interspecific positive correlation between pollen and ovule number. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the lack of negative correlation between male and female function.This work was supported by the State Key Basic Research and Development Plan, China (Grant No. G2000046804) to YHG. The authors would like to thank Peter K. Endress and two anonymous reviewers for providing critical comments and helpful suggestions, Qing-Feng Wang, Jing-Yuan Wang and Jin-Ming Chen for their helpful suggestions. Shi-Guo Sun, Jing Xia, and Qian Yu are thanked for their assistance in both the field work and laboratory phases of the project.  相似文献   
7.
Development of ovular structures in the `eucalypt group' (Eucalyteae, Myrtaceae) was investigated using scanning electron microscopy and light microscopy. Different modes of placental expansion account for the variation in initiation and arrangement of ovules and ovulodes. In Eucalyptus sensu stricto placental elongation proceeds proximally and the distally-positioned ovulodes develop from the first primordia initiated (congenital ovulodes). In Angophora, Corymbia, Arillastrum, Allosyncarpia and Stockwellia placental elongation is bi-directional and the ovulodes develop from last-initiated primordia (residual ovulodes). Bi-directional elongation and residual ovulodes are present in the outgroup taxon Lophostemon confertus and is presumably plesiomorphic. This suite of characters is potentially informative for resolving relationships for several key taxa: E. microcorys (subgenus Symphyomyrtus) has proximal placental expansion and congenital ovulodes, which is consistent with most Eucalyptus; E. curtisii (subgenus Gaubaea) has the plesiomophic condition and may be sister to all other species of Eucalyptus.  相似文献   
8.
Haploid plants were regenerated in vitro from unpollinated ovules of niger (Guizotia abyssinica (L. f.) (Cass.) on Murashige and Skoog nutrient medium (MS) supplemented with 10 μM naphthaleneacetic acid or 10 μM NAA + 1.5 μM kinetin and 30 g/l sucrose. Gamborg (B5) medium was the best for plant regeneration (in comparison with MS, Nitsch and Nitsch (NN), and Chu (N6) media) from cultured ovules, and 6.66 and 7.33 ovules of JNC-6 and Ootacamund cultivars were involved in direct plant regeneration on this medium. Matured ovules (ovules collected one day before anthesis or on the day of anthesis) only responded to cultural regimes and involved in direct plantlet development. Cytological preparation of root tips and chloroplast counts in the guard cells of leaf stomata of regenerated plants confirmed their haploid nature. This text was submitted by the authors in English.  相似文献   
9.
Abstract

In Arabidopsis thaliana, cell fate in developing ovules is determined by the action of the homeodomain factor BELL1 (BEL1) and of the MADS-box factors SEEDSTICK (STK), SHATTERPROOF1 (SHP1) and SHP2. The analysis of the bel1 and the stk shp1 shp2 mutants revealed that the functional megaspore is formed, however, it does not proceed into megagametogenesis. In the bel1 stk shp1 shp2, quadruple mutant megasporogenesis does not take place. In this article we describe a detailed morphological analysis of the quadruple mutant, and we discuss the possibility that BELL1, STK, SHP1 and SHP2 not only control integument identity determination and development, but that they might also play a role during megasporogenesis.  相似文献   
10.
未授粉子房和胚珠离体培养诱导植物雌核发育研究进展   总被引:9,自引:0,他引:9  
未授粉子房和胚珠培养离体诱导雌核发育的研究已近半个世纪,目前共有20科40余种种子植物的未授粉子房或胚珠离体培养诱导了雌核发育,但成功获得雌性单倍体的植物只有10科25种2变种。本文重点对离体雌核发育的胚胎学的研究资料进行综述,包括离体条件下胚珠中胚囊的发育状况、雌核发育的模式、雌性单倍体形成的途径以及自发胚乳的离体诱导并指出该领域研究中存在的问题,进一步在研究方法上提出了设想和建议。  相似文献   
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