Virus-like particles in normal and tumorous tissues of Drosophila

A new virus-like particle has been found in Drosophila. Thus far it has been detected only in electron micrographs of certain cells capable of division, such as those in larval imaginal disks, cell lines derived from imaginal disks, cells from a genetically controlled brain tumor, and adult gut cells. It appears to be slightly elliptical in shape, about 37 millimicrons by 45 millimicrons, and occurs in both the nucleus and cytoplasm. From the evidence it is suggested that the particle is a new virus.     

THERMALLY INDUCED GENITAL APPENDAGES ON MOSQUITOES

Temperatures above those normally present in larval sites of certain mosquitoes (for example, Aedes stimulans) cause larvae of potential males to be feminized in all degrees. Certain combinations of temperatures will affect these larvae so that an abnormal pair of genital appendages consistently appears in addition to the usual pair. These appendages appear to be masculine and are presumed to come from imaginal discs that are latent in present-day Diptera.     

Natural selection and developmental constraints in the evolution of allometries

In animals, scaling relationships between appendages and body size exhibit high interspecific variation but low intraspecific variation. This pattern could result from natural selection for specific allometries or from developmental constraints on patterns of differential growth. We performed artificial selection on the allometry between forewing area and body size in a butterfly to test for developmental constraints, and then used the resultant increased range of phenotypic variation to quantify natural selection on the scaling relationship. Our results show that the short-term evolution of allometries is not limited by developmental constraints. Instead, scaling relationships are shaped by strong natural selection.     

The control of the metabolic switch in cancers by oncogenes and tumor suppressor genes

Cells from some tumors use an altered metabolic pattern compared with that of normal differentiated adult cells in the body. Tumor cells take up much more glucose and mainly process it through aerobic glycolysis, producing large quantities of secreted lactate with a lower use of oxidative phosphorylation that would generate more adenosine triphosphate (ATP), water, and carbon dioxide. This is the Warburg effect, which provides substrates for cell growth and division and free energy (ATP) from enhanced glucose use. This metabolic switch places the emphasis on producing intermediates for cell growth and division, and it is regulated by both oncogenes and tumor suppressor genes in a number of key cancer-producing pathways. Blocking these metabolic pathways or restoring these altered pathways could lead to a new approach in cancer treatments.     

Dual origin of tissue-specific progenitor cells in Drosophila tracheal remodeling

During Drosophila metamorphosis, most larval cells die. Pupal and adult tissues form from imaginal cells, tissue-specific progenitors allocated in embryogenesis that remain quiescent during embryonic and larval life. Clonal analysis and fate mapping of single, identified cells show that tracheal system remodeling at metamorphosis involves a classical imaginal cell population and a population of differentiated, functional larval tracheal cells that reenter the cell cycle and regain developmental potency. In late larvae, both populations are activated and proliferate, spread over and replace old branches, and diversify into various stalk and coiled tracheolar cells under control of fibroblast growth factor signaling. Thus, Drosophila pupal/adult tissue progenitors can arise both by early allocation of multipotent cells and late return of differentiated cells to a multipotent state, even within a single tissue.     

Cloning,localization and expression analysis of two fw2.2-like genes in small-and large-fruited pear species

Fruit size is one of the most important agronomic characters,which is mainly determined by cell number and cell size.However,our current knowledge about pear is largely unknown.Through counting of pear mesocarp cells at different stages,we found that the cell number,rather than the cell size,is responsible for the differences between small- and large-fruited cultivars.Fruit weight-2.2(fw2.2) is an important quantitative trait locus(QTL) affecting fruit weight in tomato and functions as a negative regulator in carpel cell division.To get more insights into this QTL in pear fruit development,we isolated two putative homologous fw2.2 genes,which were designated as fw2.2-like(PbFWL) genes.PbFWLs encode Cys-rich proteins with the CCXXXXCPC motif and belong to the PLAC8 superfamily.In addition,results from the subcellular localization indicated that PbFWLs were localized in the plasma membrane.The expression profile of the PbFWL genes by qRT-PCR showed they expressed higher in small-sized fruit cultivar than that in large-sized fruit cultivar during the cell division period.In summary,our data suggest that these two PbFWLs might be negatively related to the cell division in pear fruit.     

Evidence for dust grain growth in young circumstellar disks

Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.     

Dynamics of Dpp signaling and proliferation control

Morphogens, such as Decapentaplegic (Dpp) in the fly imaginal discs, form graded concentration profiles that control patterning and growth of developing organs. In the imaginal discs, proliferative growth is homogeneous in space, posing the conundrum of how morphogen concentration gradients could control position-independent growth. To understand the mechanism of proliferation control by the Dpp gradient, we quantified Dpp concentration and signaling levels during wing disc growth. Both Dpp concentration and signaling gradients scale with tissue size during development. On average, cells divide when Dpp signaling levels have increased by 50%. Our observations are consistent with a growth control mechanism based on temporal changes of cellular morphogen signaling levels. For a scaling gradient, this mechanism generates position-independent growth rates.     

果树果实生长发育细胞学研究进展

为了从细胞学角度深入认识果树果实的生长发育动态及果实膨大机理。本文通过对果实生长的解剖结构及其调节因子的综述,论述了果实发育细胞学变化及主要影响因素。果实生长的实质是果实细胞的分裂、细胞的膨大及物质的积累与转化。果实生长发育在解剖结构上表现为果实外果皮、中果皮及内果皮三部分细胞的分裂与膨大。果实细胞的分裂与膨大除受遗传因素制约外,还受激素物质和营养物质以及温度、光照、水分等环境因素的影响。果实膨大还可通过栽培措施及植物生长调节剂加以调控。因此,果实发育细胞学研究可为优质果品的形成提供理论依据,营养物质及激素物质的精准施用必将成为今后优质果品生产的主要研究方向。     

Imaginal discs secrete insulin-like peptide 8 to mediate plasticity of growth and maturation

Developing animals frequently adjust their growth programs and/or their maturation or metamorphosis to compensate for growth disturbances (such as injury or tumor) and ensure normal adult size. Such plasticity entails tissue and organ communication to preserve their proportions and symmetry. Here, we show that imaginal discs autonomously activate DILP8, a Drosophila insulin-like peptide, to communicate abnormal growth and postpone maturation. DILP8 delays metamorphosis by inhibiting ecdysone biosynthesis, slowing growth in the imaginal discs, and generating normal-sized animals. Loss of dilp8 yields asymmetric individuals with an unusually large variation in size and a more varied time of maturation. Thus, DILP8 is a fundamental element of the hitherto ill-defined machinery governing the plasticity that ensures developmental stability and robustness.     

Cell death during early morphogenesis: parallels between insect limb and vertebrate limb development

The complex jointed leg of the adult fly is derived, in the pupal stage, from a simple lobed sac of cells. The gross morphological changes that result in adult shape are effected by a combination of differential cell growth and the programmed death of a large number of imaginal disc cells. Events are closely similar to those occurring in digit formation and limb contouring during vertebrate morphogenesis. In both cases phagocytic blood cells are intimately involved.     

Rhizoid differentiation in fern spores: experimental manipulation

Germination in spores of the fern Onoclea sensibilis is initiated by an asymmetric division that partitions the spore into two cells of unequal size. The unequal daughter cells differentiate immediately into distinct types. When spores are germinated on the surface of solutions of methanol, the initial division is symmetrical, and the daughter cells from this equal division develop into the same type of cell. The differentiation of a rhizoid from the smaller cell in untreated spores is suppressed by methanol treatment.     

滩地淹水胁迫对杨树生长与木材显微结构的影响

对5种不同淹水时间类型滩地1～10年生杨树单株材积生长动态进行了分析．结果表明。不同类型之间单株材积生长量均存在显著差异．且随着林龄增长，其差异逐步减小；不同淹水胁迫下，当年年轮宽度、纤维细胞数量、木材基本密度均存在显著差异，纤维长度和宽度差异不显著，杨树年轮宽度与径向纤维细胞数、导管数、径向纤维比量呈正相关；随淹水胁迫程度加深，当年形成层细胞分裂受到了显著抑制，纤维细胞以及导管数量减少，林木径向生长量下降．径向导管比量提高，纤维比量下降，细胞壁腔比减小，木材密度明显降低．对5种淹水类型滩地的林木生长进行了系统聚类，合并划分为4种生长类型，对其中3种常规造林宜林类型杨树生长潜力进行了预测。     

Asymmetry and aging of mycobacterial cells lead to variable growth and antibiotic susceptibility

Cells use both deterministic and stochastic mechanisms to generate cell-to-cell heterogeneity, which enables the population to better withstand environmental stress. Here we show that, within a clonal population of mycobacteria, there is deterministic heterogeneity in elongation rate that arises because mycobacteria grow in an unusual, unipolar fashion. Division of the asymmetrically growing mother cell gives rise to daughter cells that differ in elongation rate and size. Because the mycobacterial cell division cycle is governed by time, not cell size, rapidly elongating cells do not divide more frequently than slowly elongating cells. The physiologically distinct subpopulations of cells that arise through asymmetric growth and division are differentially susceptible to clinically important classes of antibiotics.     

Juvenile hormone is required to couple imaginal disc formation with nutrition in insects

In starved larvae of the tobacco hornworm moth Manduca sexta, larval and imaginal tissues stop growing, the former because they lack nutrient-dependent signals but the latter because of suppression by juvenile hormone. Without juvenile hormone, imaginal discs form and grow despite severe starvation. This hormone inhibits the intrinsic signaling needed for disc morphogenesis and does so independently of ecdysteroid action. Starvation and juvenile hormone treatments allowed the separation of intrinsic and nutrient-dependent aspects of disc growth and showed that both aspects must occur during the early phases of disc morphogenesis to ensure normal growth leading to typical-sized adults.     

胡杨横走侧根及不定芽发生的形态解剖学研究

利用常规石蜡切片法对胡杨根蘖繁殖特性进行形态解剖学研究。结果表明：胡杨横走侧根的初生木质部为三原型或四原型,周皮中栓内层较发达,由6～8层薄壁细胞组成。横走侧根横切面上次生维管组织中次生韧皮部的比例远小于次生木质部;早期形成的次生木质部以细胞壁尚未木质化的木纤维细胞数量居多为特征;维管射线很发达。胡杨的根蘖繁殖源于横走...     

高温和外源ABA对不同持绿型小麦品种籽粒发育及内源激素含量的影响

【目的】探讨花后高温和外源脱落酸（ABA）对不同持绿型小麦籽粒胚乳细胞增殖、籽粒灌浆和内源激素的影响,为高温逆境下采用激素调控措施提高粒重提供理论依据。【方法】选用持绿型汶农6号和非持绿型济麦20,花后1-5 d,用透明聚乙烯塑料膜搭设增温棚进行高温处理,同时花后1-3 d喷施10 mg?L-1的ABA于穗部,用量100 mL?m-2,3次重复。定期取籽粒样,用高效液相色谱法测定4种内源激素,用简易胚乳细胞计数法测定胚乳细胞数目,Richard方程对籽粒增重及胚乳细胞增殖动态模拟并计算相关参数。【结果】高温处理显著降低了两品种强弱势籽粒的胚乳细胞数目,降低胚乳细胞增殖速率,但延长了籽粒胚乳细胞活跃分裂期和实际分裂终期;显著降低两品种弱势籽粒的灌浆速率,缩短了两品种弱势粒的生长活跃期及实际灌浆终期。高温处理显著降低两品种千粒重和穗粒数,其中汶农6号强、弱势粒分别减少3.7和8.2 粒/穗,济麦20强、弱势粒分别减少1.3和4.3 粒/穗;显著降低两品种产量,汶农6号和济麦20产量分别降低19.65%和26.22%。常温及高温下喷施ABA均显著提高了两品种灌浆速率,提高了籽粒胚乳细胞增殖速率,扩大胚乳细胞数目。高温处理降低了强弱势籽粒ZR含量,显著提高了济麦20强、弱势粒花后3-27 d的GA3含量,显著提高汶农6号花后12-27 d的GA3含量;但降低了弱势粒花后15-27 d的IAA含量。高温处理下喷施ABA,降低了济麦20强势粒花后3-9 d ZR含量,但显著提高济麦20强势粒花后3-28 d内源ABA含量,显著提高汶农6号强势粒花后3-18 d ABA含量。常温下喷施ABA显著降低了济麦20和汶农6号强、弱势粒的GA3含量;高温下喷施ABA,显著降低了汶农6号强弱势粒的GA3含量,降低济麦20强势粒花后3-12 d的GA3含量,显著降低弱势粒花后6-15 d的GA3含量。常温下喷施ABA显著提高济麦20强势粒花后12-18 d的IAA含量;提高了汶农6号强势粒花后6-18 d IAA含量,显著提高两品种弱势粒花后6-27 d IAA含量。持绿型汶农6号的千粒重和产量均显著大于非持绿型济麦20。【结论】高温胁迫对非持绿型品种的产量和两品种弱势粒粒数影响较大,高温降低了两品种籽粒胚乳细胞数目,降低籽粒灌浆速率,最终导致粒重及产量降低。喷施外源ABA通过调节内源激素水平,促进胚乳细胞分裂,扩大了常温及高温下籽粒库容量,提高了籽粒灌浆速率,从而提高了籽粒产量。     

改变源-库比率对大豆子叶细胞数和粒大小的影响

用3个大豆品种播种于温室和大田,以研究自子叶细胞分化初期至生理成熟阶段,改变源-库比率对于叶细胞数、籽粒生长速率和粒大小的影响。研究结果表明,大豆子叶中的细胞数目是制约粒大小的重要因素,同化物的供应水平与子叶分化的细胞数目呈正相关。文中还讨论了在粒重线性增长时期,同化物的供应水平对细胞干物质积累的影响。     

影响草地早熟禾原生质体生长和分裂的生理生化因素分析

以草地早熟禾‘午夜Ⅱ号’、‘新格莱德’和‘橄榄球Ⅱ号’3个品种继代20次的愈伤组织为材料,进行原生质体培养,测定愈伤组织可溶性蛋白质含量、氨基酸含量、SOD和POX酶活性.结果表明:3个草地早熟禾品种原生质体经培养15 d后,原生质体分裂率分别为‘新格莱德’50.1％、‘午夜Ⅱ号’42.8％、‘橄榄球Ⅱ号’29.4％....