闽西北稻区"晚改中"避蚊减害技术研究与应用

针对闽西北海拔300-500m的单、双季水稻混栽区稻瘿蚊危害重、单季稻三代稻瘿蚊危害突出的情况,通过研究提出“晚改中”的依据和技术,在正常年份下,把以往5月份播种的单季稻的播种期提早到4月5日前,就可以有效地避开三代稻瘿蚊的危害,而不必提早到3月20日前,与农民农时操作习惯更吻合,农民更易接受采用。     

Kinetics of the dimerization of retroviral proteases: the "fireman's grip" and dimerization

All retroviral proteases belong to the family of aspartic proteases. They are active as homodimers, each unit contributing one catalytic aspartate to the active site dyad. An important feature of all aspartic proteases is a conserved complex scaffold of hydrogen bonds supporting the active site, called the "fireman's grip," which involves the hydroxyl groups of two threonine (serine) residues in the active site Asp-Thr(Ser)-Gly triplets. It was shown previously that the fireman's grip is indispensable for the dimer stability of HIV protease. The retroviral proteases harboring Ser in their active site triplet are less active and, under natural conditions, are expressed in higher enzyme/substrate ratio than those having Asp-Thr-Gly triplet. To analyze whether this observation can be attributed to the different influence of Thr or Ser on dimerization, we prepared two pairs of the wild-type and mutant proteases from HIV and myeloblastosis-associated virus harboring either Ser or Thr in their Asp-Thr(Ser)-Gly triplet. The equilibrium dimerization constants differed by an order of magnitude within the relevant pairs. The proteases with Thr in their active site triplets were found to be approximately 10 times more thermodynamically stable. The dimer association contributes to this difference more than does the dissociation. We propose that the fireman's grip might be important in the initial phases of dimer formation to help properly orientate the two subunits of a retroviral protease. The methyl group of threonine might contribute significantly to fixing such an intermediate conformation.     

Biology of the mason bee Osmia latreillei (Hymenoptera: Megachilidae) under artificial nesting conditions in Egypt

The mason bee Osmia (Helicosmia) latreillei Spinola is one of the dominant species of bees throughout Egypt, and can be found commonly in the Suez Canal Region. The species visits numerous plant species of the family Asteraceae and is considered the most important pollinator of certain crops such as sunflower. This species and some other solitary cavity nesting bees are threatened by fragmentation of their nesting habitats. Several attempts were made to establish and propagate O. latreillei, and success was achieved for re-nesting it in various artificial materials such as wood and polystyrene with rolled paper straws. These artificial nests were established at the conservation area of the Bee Research Centre, Suez Canal University, in order to study the nesting behavior and biology of O. latreillei under artificial conditions and to document their natural enemies. Biologically, there was no significance difference between the life cycle of O. latreillei under natural and artificial nesting conditions. This solitary bee was univoltine, individuals active only during Spring, and attacked by diverse enemies, with Stelis (Stelis) murina Pérez and chrysidid wasps considered the two most major pests of this wild bee species.     

海南霸王岭南亚松天然林群落遗传多样性的SSR分析

为揭示海南霸王岭南亚松天然林群落在遗传多样性水平上的差异和遗传分化情况,利用SSR分子标记技术对其6个群落共350个单株进行了遗传多样性分析。结果显示:所选用的12对SSR引物,共检测到38个等位位点。各区域间观察杂合度(Ho)、期望杂合度(He)、Shannon信息指数(I)和Nei’s期望杂合度分别介于0.1933~0.4679、0.4150~0.5321、0.5225~0.7384、0.3451~0.4819之间,说明霸王岭南亚松总体的遗传多样性水平相对较低。居群间的遗传分化系数(Fst)平均为0.0628,说明绝大部分变异(93.72%)存在于群体各居群内。UPGMA聚类可将供试6个群落划分为2类,遗传距离与地理距离有一定相关性,但并没有严格按地理距离聚类,受到了自然地理隔离的影响。     

Some studies on the metabolism of labelled molybdenum compounds in cattle

An initial experiment showed that [99Mo]di- and trithiomolybdates could be detected in bovine plasma after the introduction of [99Mo]molybdate into the rumen. It was felt that this justified the use of [99Mo]trithiomolybdate for the subsequent studies made of plasma thiomolybdate metabolism in vivo in cattle. Rapid intravenous injection of [99Mo]trithiomolybdate into cattle showed that doses of 50 mg Mo were subject to extensive hydrolysis over the first few minutes postinjection, but at lower dose rates this was reduced so that tracer doses (less than 1.5 mg Mo) were relatively stable. The plasma metabolism was unaffected by copper status within the limits of the experiments (that is, liver copper levels down to 9 mg/kg d.m.) The disappearance of [99Mo] and [35S]trithiomolybdate (1 mg Mo) from plasma was delayed for up to 10 hr by the immediate preinjection of copper, although no chemical modification of the thiomolybdate appeared to occur.     

X-ray Structures of the Post-fusion 6-Helix Bundle of the Human Syncytins and their Functional Implications

The retroviral envelope-derived proteins syncytin-1 and syncytin-2 (syn1 and syn2) drive placentation in humans by forming a syncytiotophoblast, a structure allowing for an exchange interface between maternal and fetal blood during pregnancy. Despite their essential role, little is known about the molecular mechanism underlying the syncytins' function. We report here the X-ray structures of the syn1 and syn2 transmembrane subunit ectodomains, featuring a 6-helix bundle (6HB) typical of the post-fusion state of gamma-retrovirus and filovirus fusion proteins. Contrary to the filoviruses, for which the fusion glycoprotein was crystallized both in the post-fusion and in the spring-loaded pre-fusion form, the highly unstable nature of the syncytins' prefusion form has precluded structural studies. We undertook a proline-scanning approach searching for regions in the syn1 6HB central helix that tolerate the introduction of helix-breaker residues and still fold correctly in the pre-fusion form. We found that there is indeed such a region, located two α-helical turns downstream a stutter in the central coiled-coil helix - precisely where the breaks of the spring-loaded helix of the filoviruses map. These mutants were fusion-inactive as they cannot form the 6HB, similar to the “SOSIP” mutant of HIV Env that allowed the high-resolution structural characterization of its labile pre-fusion form. These results now open a new window of opportunity to engineer more stable variants of the elusive pre-fusion trimer of the syncytins and other gamma-retroviruses envelope proteins for structural characterization.