Asymmetric leaves1 mediates leaf patterning and stem cell function in Arabidopsis

Meristem function in plants requires both the maintenance of stem cells and the specification of founder cells from which lateral organs arise. Lateral organs are patterned along proximodistal, dorsoventral and mediolateral axes. Here we show that the Arabidopsis mutant asymmetric leaves1 (as1) disrupts this process. AS1 encodes a myb domain protein, closely related to PHANTASTICA in Antirrhinum and ROUGH SHEATH2 in maize, both of which negatively regulate knotted-class homeobox genes. AS1 negatively regulates the homeobox genes KNAT1 and KNAT2 and is, in turn, negatively regulated by the meristematic homeobox gene SHOOT MERISTEMLESS. This genetic pathway defines a mechanism for differentiating between stem cells and organ founder cells within the shoot apical meristem and demonstrates that genes expressed in organ primordia interact with meristematic genes to regulate shoot morphogenesis.     

Retinoic acid coordinates somitogenesis and left-right patterning in vertebrate embryos

A striking feature of the body plan of a majority of animals is bilateral symmetry. Almost nothing is known about the mechanisms controlling the symmetrical arrangement of the left and right body sides during development. Here we report that blocking the production of retinoic acid (RA) in chicken embryos leads to a desynchronization of somite formation between the two embryonic sides, demonstrated by a shortened left segmented region. This defect is linked to a loss of coordination of the segmentation clock oscillations. The lateralization of this defect led us to investigate the relation between somitogenesis and the left-right asymmetry machinery in RA-deficient embryos. Reversal of the situs in chick or mouse embryos lacking RA results in a reversal of the somitogenesis laterality defect. Our data indicate that RA is important in buffering the lateralizing influence of the left-right machinery, thus permitting synchronization of the development of the two embryonic sides.     

Developmental basis of limblessness and axial patterning in snakes.

The evolution of snakes involved major changes in vertebrate body plan organization, but the developmental basis of those changes is unknown. The python axial skeleton consists of hundreds of similar vertebrae, forelimbs are absent and hindlimbs are severely reduced. Combined limb loss and trunk elongation is found in many vertebrate taxa, suggesting that these changes may be linked by a common developmental mechanism. Here we show that Hox gene expression domains are expanded along the body axis in python embryos, and that this can account for both the absence of forelimbs and the expansion of thoracic identity in the axial skeleton. Hindlimb buds are initiated, but apical-ridge and polarizing-region signalling pathways that are normally required for limb development are not activated. Leg bud outgrowth and signalling by Sonic hedgehog in pythons can be rescued by application of fibroblast growth factor or by recombination with chick apical ridge. The failure to activate these signalling pathways during normal python development may also stem from changes in Hox gene expression that occurred early in snake evolution.     

Conserved factors regulate signalling in Arabidopsis thaliana shoot and root stem cell organizers

Throughout the lifespan of a plant, which in some cases can last more than one thousand years, the stem cell niches in the root and shoot apical meristems provide cells for the formation of complete root and shoot systems, respectively. Both niches are superficially different and it has remained unclear whether common regulatory mechanisms exist. Here we address whether root and shoot meristems use related factors for stem cell maintenance. In the root niche the quiescent centre cells, surrounded by the stem cells, express the homeobox gene WOX5 (WUSCHEL-RELATED HOMEOBOX 5), a homologue of the WUSCHEL (WUS) gene that non-cell-autonomously maintains stem cells in the shoot meristem. Loss of WOX5 function in the root meristem stem cell niche causes terminal differentiation in distal stem cells and, redundantly with other regulators, also provokes differentiation of the proximal meristem. Conversely, gain of WOX5 function blocks differentiation of distal stem cell descendents that normally differentiate. Importantly, both WOX5 and WUS maintain stem cells in either a root or shoot context. Together, our data indicate that stem cell maintenance signalling in both meristems employs related regulators.     

Sonic hedgehog function in chondrichthyan fins and the evolution of appendage patterning

The genetic mechanisms regulating tetrapod limb development are well characterized, but how they were assembled during evolution and their function in basal vertebrates is poorly understood. Initial studies report that chondrichthyans, the most primitive extant vertebrates with paired appendages, differ from ray-finned fish and tetrapods in having Sonic hedgehog (Shh)-independent patterning of the appendage skeleton. Here we demonstrate that chondrichthyans share patterns of appendage Shh expression, Shh appendage-specific regulatory DNA, and Shh function with ray-finned fish and tetrapods. These studies demonstrate that some aspects of Shh function are deeply conserved in vertebrate phylogeny, but also highlight how the evolution of Shh regulation may underlie major morphological changes during appendage evolution.     

砧木年龄对美国山核桃嫁接苗光合特性的影响

为研究砧木年龄与嫁接苗生长的关系,笔者对3年生、5年生和9年生美国山核桃砧木嫁接苗的新梢生长特征进行分析,并比较了它们新梢叶片叶绿素含量及荧光、光合特性的差异。结果表明:不同年龄美国山核桃砧木嫁接苗新梢平均长度和粗度均是9年生>5年生>3年生; 砧木年龄越大,其嫁接苗新梢叶片的净光合速率、叶绿素含量、水分利用效率越高,蒸腾速率越小。试验结果说明砧木年龄越大,嫁接苗的光合能力及抗旱能力越强。     

ATPG is required for the accumulation and function of chloroplast ATP synthase in Arabidopsis

The subunit Ⅱ of chloroplast ATP synthase is one of the two peripheral stalks, which associates the catalytic CF1 with mem-brane-spanning CFo . Although the structural and functional roles of chloroplast ATP synthase have been extensively examined, the physiological significance of subunit Ⅱ in vivo is still unclear. In this work, we identified one Arabidopsis T-DNA insertion mutant of atpG gene encoding the subunit Ⅱ of chloroplast ATP synthase. The atpg null mutant displayed an albino lethal pheno-type, as it could not grow photoautotrophically. Transmission electron microscopy analysis showed that chloroplasts of atpg lacked the organized thylakoid membranes. Loss of subunit Ⅱ affected the accumulation of CF1-CFo complex, however, it did not seem to have an effect on the CF1 assembly. The light induced ATP formation of atpg was significantly reduced compared with the wild type. Based on these results, we suggested that ATPG was essential for the accumulation and function of chloroplast ATP synthase.     

一种功能性轴向配位基的合成

二氧四胺大环(macrocyclic dioxotetraanine)配体因其独特的结构特点和性质而受到广泛的重视和关注.本文合成了一种溴代杂环8—溴代甲基喹淋,并作为功能性轴向给体侧臂成功地引入到十三员、十四员二氧四胺大环骨架上,发现喹啉侧臂的引入,改变了大环配体的配位环境并产生新的性质和功能     

Axial patterning in cephalochordates and the evolution of the organizer

The organizer of the vertebrate gastrula is an important signalling centre that induces and patterns dorsal axial structures. Although a topic of long-standing interest, the evolutionary origin of the organizer remains unclear. Here we show that the gastrula of the cephalochordate amphioxus expresses dorsal/ventral (D/V) patterning genes (for example, bone morphogenetic proteins (BMPs), Nodal and their antagonists) in patterns reminiscent of those of their vertebrate orthlogues, and that amphioxus embryos, like those of vertebrates, are ventralized by exogenous BMP protein. In addition, Wnt-antagonists (for example, Dkks and sFRP2-like) are expressed anteriorly, whereas Wnt genes themselves are expressed posteriorly, consistent with a role for Wnt signalling in anterior/posterior (A/P) patterning. These results suggest evolutionary conservation of the mechanisms for both D/V and A/P patterning of the early gastrula. In light of recent phylogenetic analyses placing cephalochordates basally in the chordate lineage, we propose that separate signalling centres for patterning the D/V and A/P axes may be an ancestral chordate character.     

Role of PHABULOSA and PHAVOLUTA in determining radial patterning in shoots

The upper side of the angiosperm leaf is specialized for efficient capture of sunlight whereas the lower side is specialized for gas exchange. In Arabidopsis, the establishment of polarity in the leaf probably requires the generation and perception of positional information along the radial (adaxial versus abaxial or central versus peripheral) dimension of the plant. This is because the future upper (adaxial) side of the leaf develops from cells closer to the centre of the shoot, whereas the future under (abaxial) side develops from cells located more peripherally. Here we implicate the Arabidopsis PHABULOSA and PHAVOLUTA genes in the perception of radial positional information in the leaf primordium. Dominant phabulosa (phb) and phavoluta (phv) mutations cause a dramatic transformation of abaxial leaf fates into adaxial leaf fates. They do so by altering the predicted sterol/lipid-binding domains of ATHB14 and ATHB9, proteins of previously unknown function that also contain DNA-binding motifs. This change probably renders the protein constitutively active, implicating this domain as a central regulator of protein function and the PHB and PHV proteins as receptors for an adaxializing signal.     

AutoCAD及全站仪在极坐标法放样中的应用

结合自已的工作体会,对A u toCAD、全站仪在极坐标法放样中内业资料及外业中的应用作了简略的阐述,并提出了自已的一些看法.     

预裂爆破轴向不耦合系数的分析计算

以爆炸气体动力学和岩石力学理论为基础，分析预裂爆破轴向不耦合装药的作用原理和成缝机理，得出了轴向不耦合系数在不同条件下的取值范围，计算值也现场实际工程十分接近，为工程提供了可供参考的理论和计算方法。