甘蓝型油菜油体数量及面积之和与含油量的相关性

利用荧光染料尼罗红染色和激光扫描共聚焦显微观察技术,建立了油菜油体观察或生物体内中性脂类物质定性鉴定的研究体系。对高油品种宁油14号、宁油18号、ZH-088和低油品种ZL-366、NjY008、Westar共6个甘蓝型油菜品种子叶贮藏细胞内的油体进行了观察。研究发现：油菜种子成熟过程中,油体从着色不明显的小颗粒,逐渐发育形成着色清晰的球状大油体。种子成熟干燥后,油体间很少发生聚合。在成熟干燥的种子中,油体集中分布于子叶贮藏细胞中央,呈椭圆形或不规则形状,较少为圆形。通过研究种子内油体与含油量的关系,发现高油品种组与低油品种组之间在单个子叶贮藏细胞内油体数量和截面积之和存在明显差异,而在高油品种组内或低油品种组内的差异不明显。结果显示,油菜种子细胞中油体的数量和总面积与含油量之间存在正相关,可作为高油分材料的选择依据。     

SLOW WALKER2, a NOC1/MAK21 Homologue,Is Essential for Coordinated Cell Cycle Progression during Female Gametophyte Development in Arabidopsis

Morphogenesis requires the coordination of cell growth, division, and cell differentiation. Female gametogenesis in flowering plants, where a single haploid spore undergoes continuous growth and nuclear division without cytokinesis to form an eight-nucleate coenocytic embryo sac before cellularization, provides a good system to study the genetic control of such processes in multicellular organisms. Here, we report the characterization of an Arabidopsis (Arabidopsis thaliana) female gametophyte mutant, slow walker2 (swa2), in which the progression of the mitotic cycles and the synchrony of female gametophyte development were impaired, causing an arrest of female gametophytes at the two-, four-, or eight-nucleate stage. Delayed pollination test showed that a portion of the mutant ovules were able to develop into functional embryo sacs and could be fertilized. SWA2 encodes a nucleolar protein homologous to yeast NUCLEOLAR COMPLEX ASSOCIATED PROTEIN1 (NOC1)/MAINTENANCE OF KILLER21 that, together with NOC2, is involved in preribosome export from the nucleus to the cytoplasm. Similarly, SWA2 can physically interact with a putative Arabidopsis NOC2 homologue. SWA2 is expressed ubiquitously throughout the plant, at high levels in actively dividing tissues and gametophytes. Therefore, we conclude that SWA2 most likely plays a role in ribosome biogenesis that is essential for the coordinated mitotic progression of the female gametophyte.Morphogenesis requires tightly coordinated coupling of cellular activities, such as cell growth, cell division, and differentiation. In past decades, significant progress on cell cycle control has been achieved mostly in single-celled organisms and cultured mammalian cells. The elucidation of the cyclin/cyclin-dependent kinase checkpoint control, for example, provides insight into molecular mechanisms on how and when cells divide. Mechanisms coupling cell growth to environmental and developmental signals have also been investigated. Ribosome biogenesis, a key for rapid cell growth, is coupled with nutrient availability and stress signals via the TOR signaling pathway (Warner et al., 2001; Wullischleger et al., 2006). However, questions such as how the cell senses intrinsic cellular homeostatic signals remain to be addressed. For example, how ribosome dynamics and translational activities are measured and coupled to cytokinesis and cell differentiation, especially in the context of development of multicellular organisms.Female gametogenesis in Arabidopsis (Arabidopsis thaliana) is a unique system to address such questions in multicellular organisms. During female gametogenesis, the haploid functional megaspore undergoes continuous cell growth and three cycles of consecutive nuclear division without cytokinesis, giving rise to a giant eight-nucleate, coenocytic cell: the embryo sac. The size of the embryo sac increases about 6-fold without cytokinesis until it reaches its maximum during gametogenesis in maize (Zea mays; Dow and Mascarenhas, 1991). The two polar nuclei migrate toward the micropylar half of the embryo sac and eventually fuse to give rise to a diploid nucleus of the central cell. As the polar nuclei migrate, cellularization takes place simultaneously to divide the coenocytic embryo sac into seven cells of four cell fates: three antipodal cells, two synergid cells, one egg cell, and one central cell (Drews et al., 1998; Grossniklaus and Schneitz, 1998; Yang and Sundaresan, 2000; Wilson and Yang, 2004). Obviously, its haploid nature and coupling of cell growth, division, and cell fates make the female gametophyte a nice system to investigate how these cellular activities are coordinated in development.The temporal and spatial control of cell growth, the mitotic division cycles, and cell fate specification during female gametogenesis have been the focus of sexual plant reproduction research. Recently, genetic studies have identified gametophytic mutations that start to shed light on the genetic and molecular control of these processes. Mutations in genes involved in diverse cellular functions, including ANDARTA (Howden et al., 1998), GAMETOPHYTIC FACTOR1 (GFA1; Christensen et al., 1997), HADAD (Moore et al., 1997), LETHAL OVULE2 (Sheridan and Huang, 1997), LYSOPHOSPHATIDYL ACYLTRANSFERASE (Kim et al., 2005), NOMEGA (Kwee and Sundaresan, 2003), PROLIFERA (Springer et al., 1995), SLOW WALKER1 (SWA1; Shi et al., 2005), SUCCINATE DEHYDROGENASE (Leon et al., 2007), and TISTRYA (Howden et al., 1998), all result in defective gametophytic cell divisions, implying that progression of the mitotic cycle is critical for the formation of a functional female gametophyte. Loss-of-function mutations in the Arabidopsis RETINOBLASTOMA-RELATED PROTEIN1, a key negative regulator controlling the G1/S transition of the cell cycle, result in uncontrolled nuclear proliferation and cell fates, giving rise to embryo sacs with supernumerary nuclei that are irregular in size and partially enclosed by cell wall-like structures (Ebel et al., 2004). Loss of functions in CYTOKININ INDEPENDENT1 (Hejatko et al., 2003), DIANA/AGAMOUS-LIKE61 (Bemer et al., 2008), AGAMOUS-LIKE80 (Portereiko et al., 2006a), and NUCLEAR FUSION DEFECTIVE1 (Portereiko et al., 2006b) affect polar nuclear fusion and central cell development.Accumulating data suggest a key role of the nucleolus in cell survival and proliferation (Cockell and Gasser, 1999; Shaw and Doonan, 2005). A number of nucleolar proteins have been discovered to be involved in linking cell proliferation control and ribosome biogenesis in yeast (Srivastava and Pollard, 1999; Du and Stillman, 2002; Jorgensen et al., 2002; Zhang et al., 2002; Bernstein et al., 2007). Mutations in genes involved in RNA processing, including SWA1 (Shi et al., 2005), GFA1/CLO1, and ATROPOS (ATO; Moll et al., 2008; Liu et al., 2009; Yagi et al., 2009), lead to slow progression of the division cycle during female gametogenesis. Intriguingly, mutation in LACHESIS (LIS), coding for a putative splicing factor, promotes egg cell fate in the synergid and the central cell at the expense of the synergid and central cell fate (Groß-Hardt et al., 2007), suggesting that LIS plays a pivotal role in suppressing the egg cell fate in the synergid and the central cell as well as the central cell fate in antipodal cells. Similarly, cell fate changes have also been observed in gfa1/clo1 and ato mutants (Moll et al., 2008). These data imply that RNA processing and ribosome biogenesis play a key role in coordinating cell cycle progression and cell fate. Here, we report the genetic and molecular characterization of a swa2 mutation that impairs cell growth and cell division in Arabidopsis. SWA2 encodes a nucleolar protein homologous to yeast NUCLEOLAR COMPLEX ASSOCIATED PROTEIN1 (NOC1)/MAINTENANCE OF KILLER21 (MAK21) that is essential for ribosome biogenesis in yeast. We also show that SWA2 interacts physically with NOC2 homologues in yeast cells. Together, these data indicate that SWA2 is most likely involved in ribosome biogenesis and essential for cell cycle progression in female gametophyte development in Arabidopsis.     

Targeted degradation of the cyclin-dependent kinase inhibitor ICK4/KRP6 by RING-type E3 ligases is essential for mitotic cell cycle progression during Arabidopsis gametogenesis

Following meiosis, plant gametophytes develop through two or three rounds of mitosis. Although the ontogeny of gametophyte development has been defined in Arabidopsis thaliana, the molecular mechanisms regulating mitotic cell cycle progression are not well understood. Here, we report that RING-H2 group F 1a (RHF1a) and RHF2a, two RING-finger E3 ligases, play an important role in Arabidopsis gametogenesis. The rhf1a rhf2a double mutants are defective in the formation of male and female gametophytes due to interphase arrest of the mitotic cell cycle at the microspore stage of pollen development and at female gametophyte stage 1 of embryo sac development. We demonstrate that RHF1a directly interacts with and targets a cyclin-dependent kinase inhibitor ICK4/KRP6 (for Interactors of Cdc2 Kinase 4/Kip-related protein 6) for proteasome-mediated degradation. Inactivation of the two redundant RHF genes leads to the accumulation of ICK4/KRP6, and reduction of ICK4/KRP6 expression largely rescues the gametophytic defects in rhf1a rhf2a double mutants, indicating that ICK4/KRP6 is a substrate of the RHF E3 ligases. Interestingly, in situ hybridization showed that ICK4/KRP6 was predominantly expressed in sporophytes during meiosis. Our findings indicate that RHF1a/2a-mediated degradation of the meiosis-accumulated ICK4/KRP6 is essential to ensure the progression of subsequent mitoses to form gametophytes in Arabidopsis.     

植物雌配子体发育研究进展

高等植物雌配子体的形成涉及孢原细胞和大孢子母细胞的确立与分化、大孢子发生、功能大孢子以及胚囊的形成和发育等多种复杂调控过程。随着当代生物技术及功能基因组学的发展, 近年对雌配子体发育的研究已从细胞学描述逐渐过渡到对基因和发育调控分子机理的探索。以拟南芥、水稻和玉米等模式植物为材料进行的相关研究, 丰富了人们对于植物雌配子体和其它有性生殖过程遗传调控机理的认识。本文着重阐述了植物雌配子体发生和发育过程, 并综述了这一领域最新研究进展。     

甘蓝型油菜油体数量及面积之和与含油量的相关性

利用荧光染料尼罗红染色和激光扫描共聚焦显微观察技术, 建立了油菜油体观察或生物体内中性脂类物质定性鉴定的研究体系。对高油品种宁油14号、宁油18号、ZH-088和低油品种ZL-366、NjY008、Westar共6个甘蓝型油菜品种子叶 贮藏细胞内的油体进行了观察。研究发现: 油菜种子成熟过程中, 油体从着色不明显的小颗粒, 逐渐发育形成着色清晰的球状大油体。种子成熟干燥后, 油体间很少发生聚合。在成熟干燥的种子中, 油体集中分布于子叶贮藏细胞中央, 呈椭圆形或不规则形状, 较少为圆形。通过研究种子内油体与含油量的关系, 发现高油品种组与低油品种组之间在单个子叶贮藏细胞内油体数量和截面积之和存在明显差异, 而在高油品种组内或低油品种组内的差异不明显。结果显示, 油菜种子细胞中油体的数量和总面积与含油量之间存在正相关, 可作为高油分材料的选择依据。     

非特异性DNA的催化活性(Ⅰ)──应用酚试剂及FeCl_3检测DNA的酯酶活性

分别应用酚试剂与ＦｅＣｌ３来检测萘酚,表明ＤＮＡ能催化乙酸萘酯的水解,印证了以前关于ＤＮＡ具有酯酶活性的结论．ＦｅＣｌ３法可以作为检测ＤＮＡ酯酶活性的一种定量方法．     

植物雌配子体发育研究进展

高等植物雌配子体的形成涉及孢原细胞和大孢子母细胞的确立与分化、大孢子发生、功能大孢子以及胚囊的形成和发育等多种复杂调控过程。随着当代生物技术及功能基因组学的发展,近年对雌配子体发育的研究已从细胞学描述逐渐过渡到对基因和发育调控分子机理的探索。以拟南芥、水稻和玉米等模式植物为材料进行的相关研究,丰富了人们对于植物雌配子体和其它有性生殖过程遗传调控机理的认识。本文着重阐述了植物雌配子体发生和发育过程,并综述了这一领域最新研究进展。