喀斯特自然土壤中AM真菌对先锋植物根系的影响

【目的】研究丛枝菌根(Arbuscular mycorrhiza，AM)真菌在喀斯特自然土壤条件下对喀斯特先锋草本植物根系的影响。【方法】通过自然土接种AM真菌(N)、灭菌土接种AM真菌(M)及灭菌土壤对照(S)共3种土壤处理，种植喀斯特先锋植物狗尾草(Setaria viridis)、荩草(Arthraxon hispidus)、鬼针草(Bidens pilosa)及狼杷草(Bidens tripartita)，并测定它们的根系生物量、根长、根表面积、根体积、根平均直径、根尖数及根分枝数。【结果】荩草、鬼针草及狼杷草在N处理及M处理下具有较高的菌根侵染率，狗尾草的菌根侵染率较低。与S处理相比，M处理下AM真菌明显提高了荩草、鬼针草及狼杷草的根系生物量、根长、根表面积、根体积、根尖数、根分枝数及组织密度，降低了根平均直径、比根长、比根面积及比根体积；与M处理相比，N处理明显降低了荩草、鬼针草及狼杷草的根系生物量、根长、根表面积、根体积、根尖数、根分枝数及组织密度，提高了比根长、比根面积及比根体积，但对根平均直径无明显影响。【结论】荩草、鬼针草及狼杷草具有较高菌根侵染率，能与AM真菌共生获得更加发达的根系，而自然土壤削弱了AM真菌对荩草、鬼针草及狼杷草根系生长的促进作用。     

The so-called red impurity of trypan blue

Zusammenfassung Die sogenannte rote Verunreinigung von Trypanblau wurde als Gemisch von 3 Azofarbstoffen erkannt, voneinander getrennt und in ihrer Struktur aufgeklärt. Eine dieser Substanzen scheint für die kanzerogene Aktivität des kommerziellen Trypanblaus verantwortlich zu sein.     

Structural evidence for dimerization-regulated activation of an integral membrane phospholipase.

Dimerization is a biological regulatory mechanism employed by both soluble and membrane proteins. However, there are few structural data on the factors that govern dimerization of membrane proteins. Outer membrane phospholipase A (OMPLA) is an integral membrane enzyme which participates in secretion of colicins in Escherichia coli. In Campilobacter and Helicobacter pylori strains, OMPLA is implied in virulence. Its activity is regulated by reversible dimerization. Here we report X-ray structures of monomeric and dimeric OMPLA from E. coli. Dimer interactions occur almost exclusively in the apolar membrane-embedded parts, with two hydrogen bonds within the hydrophobic membrane area being key interactions. Dimerization results in functional oxyanion holes and substrate-binding pockets, which are absent in monomeric OMPLA. These results provide a detailed view of activation by dimerization of a membrane protein.     

X-ray structure of phospholipase A2 complexed with a substrate-derived inhibitor

Phospholipases A2 play a part in a number of physiologically important cellular processes such as inflammation, blood platelet aggregation and acute hypersensitivity. These processes are all initiated by the release of arachidonic acid from cell membranes which is catalysed by intracellular phospholipases A2 and followed by conversion of arachidonic acid to prostaglandins, leukotrienes or thromboxanes. An imbalance in the production of these compounds can lead to chronic inflammatory diseases such as rheumatoid arthritis and asthma. Inhibitors of phospholipase A2 might therefore act to reduce the effects of inflammation, so structural information about the binding of phospholipase A2 to its substrates could be helpful in the design of therapeutic drugs. The three-dimensional structure is not known for any intracellular phospholipase A2, but these enzymes share significant sequence homology with secreted phospholipases, for which some of the structures have been determined. Here we report the structure of a complex between an extracellular phospholipase A2 and a competitively inhibiting substrate analogue, which reveals considerable detail about the interaction and suggests a mechanism for catalysis by this enzyme.     

Ionic colloidal crystals of oppositely charged particles

Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behaviour as atoms or molecules, with the nano- to micrometre size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equilibrium phases. However, spherically symmetric, long-range attractions (that is, ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to atomic systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external electric field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behaviour of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the production of binary crystals of micrometre-sized particles, which could find use as advanced materials for photonic applications.     

Monocytes and their pathophysiological role in Crohn’s disease

Our immune system shows a stringent dichotomy, on the one hand displaying tolerance towards commensal bacteria, but on the other hand vigorously combating pathogens. Under normal conditions the balance between flora tolerance and active immunity is maintained via a plethora of dynamic feedback mechanisms. If, however, the balancing act goes faulty, an inappropriate immune reaction towards an otherwise harmless intestinal flora causes disease, Crohn’s disease for example. Recent developments in the immunology and genetics of mucosal diseases suggest that monocytes and their derivative cells play an important role in the pathophysiology of Crohn’s disease. In our review, we summarize the recent studies to discuss the dual function of monocytes - on the one hand the impaired monocyte function initiating Crohn’s disease, and on the other hand the overactivation of monocytes and adaptive immunity maintaining the disease. With a view to developing new therapies, both aspects of monocyte functions need to be taken into account. Received 1 June 2008; received after revision 24 July 2008; accepted 13 August 2008     

基于并行工程的产品开发过程管理的研究

并行工程采用集成化与并行化的思想来开发产品,强调在信息集成基础上的过程集成,运用工作流管理技术能够很好地达到此目的。在分析工作流管理技术的基础上,以冲压模具的开发过程为例来说明用工作流管理技术实现产品开发过程管理的