绥宁河生态修复对粒径分级叶绿素a的影响

通过对上海市的苏州河支流绥宁河治理段与非治理段水体叶绿素a分粒级分析,探讨了生态修复对水体粒径分级叶绿素a的影响．结果表明,非治理和对照以及治理采样点微型和微微型浮游植物叶绿素a占总叶绿素a的百分比均值分别为85．232、92．402和95．205％,其中微型浮游植物叶绿素a占总叶绿素a的百分比均值分别为78．460、87．943和87．211％,对全河叶绿素a的贡献平均为84．538％,是该水体叶绿素a生物量的最大贡献者;网采浮游植物对全河叶绿素a的贡献仅为9．054％．生态修复工程试验使网采浮游植物相对生物量减少,微型浮游植物相对生物量保持稳定,而微微型浮游植物相对生物量增多,对超微型浮游植物的影响不大,微型和微微型浮游植物对工程试验的反应最敏感．     

Programmed cell death during development of cowpea (Vigna unguiculata (L.) Walp.) seed coat

The seed coat develops primarily from maternal tissues and comprises multiple cell layers at maturity, providing a metabolically dynamic interface between the developing embryo and the environment during embryogenesis, dormancy and germination of seeds. Seed coat development involves dramatic cellular changes, and the aim of this research was to investigate the role of programmed cell death (PCD) events during the development of seed coats of cowpea [Vigna unguiculata (L.) Walp.]. We demonstrate that cells of the developing cowpea seed coats undergo a programme of autolytic cell death, detected as cellular morphological changes in nuclei, mitochondria, chloroplasts and vacuoles, DNA fragmentation and oligonucleosome accumulation in the cytoplasm, and loss of membrane viability. We show for the first time that classes 6 and 8 caspase‐like enzymes are active during seed coat development, and that these activities may be compartmentalized by translocation between vacuoles and cytoplasm during PCD events.     

Structural and functional differentiation of two clinally distributed glucosephosphate isomerase allelic isozymes from the teleost Fundulus heteroclitus

The teleost Fundulus heteroclitus (L.) possesses two loci, Gpi-A and Gpi-B, for the glycolytic enzyme, glucose-phosphate isomerase (GPI; D- glucose-6-phosphate ketol-isomerase; E.C. 5.3.1.9). The Gpi-B locus is polymorphic in Fundulus, with two common alleles, Gpi-Bb and Gpi-Bc, distributed in a clinal manner in populations along the east coast of North America. Since this clinal distribution is strongly correlated with a temperature gradient, we asked whether the GPI-B2 allozymes were functionally adapted to the thermal environment in which a given phenotype predominated. The two major GPI-B2 allozymes were purified to homogeneity and were characterized as to molecular weight, isoelectric pH, thermal denaturation, and kinetic parameters. Both GPI-Bb2 and GPI- Bc2 allozymes have molecular masses of 110 kD, and they have isoelectric pHs of 6.4 and 6.6, respectively. The GPI-Bb2 allozyme was more stable to thermal denaturation than was the GPI-Bc2 enzyme. Kinetic properties of the allelic isozymes were investigated both as a function of pH and as a function of temperature. At 25 degrees C, over the pH range considered, there were no significant differences between allozymes, either in Km for fructose-6-phosphate or in Ki for 6- phosphogluconate, but apparent Vmax values differed between pH 7.5 and pH 8.5. All steady-state kinetic parameters showed strong temperature dependence, but the allozymes differed only in the Ki for 6- phosphogluconate at temperatures greater than 30 degrees C. On the basis of the observed structural and functional differences alluded to above, the hypothesis that the major allelic isozymes of the Gpi-B locus were functionally equivalent was rejected. However, it is not yet known whether these structural and functional differences have any significance at higher levels of biological organization.      

“早期接触临床”教学模式在“医学微生物学”课程改革中的探索

“早期接触临床、进入医生角色”是21世纪我国高等医学教育改革的主流方向。立足现行临床医学专业五年制“医学微生物学”教学模式的不足,从理论和实践教学两方面进行改革,增加“早期接触临床”理念的理论课、讨论课和见习课,构建适合本课程的“早期接触临床”教学模式。通过期末考试卷面成绩分析及问卷调查评价教学效果。结果表明“早期接触临床”教学模式可有效整合基础理论与临床实践,激发学生的学习动力,并在一定程度上提高学生的学习成绩和综合分析能力,同时加深学生对医学和职业的理解。     

Transpiration of trees and forest stands: short and long-term monitoring using sapflow methods

We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement. Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985). Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell. A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend. For modelling purposes, tree canopy conductance (g_c) was calculated from Penman-Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of g_c for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.     

Sabellaria wilsoni sp.n. (Polychaeta, Sabellariidae) from the southeast coast of Brazil

A new species of Sabellaria is described from the southeast coast of Brazil and compared with related species known from South or North America.     

Population genetics and conservation of critically small cycad populations: a case study of the Albany Cycad,Encephalartos latifrons (Lehmann)

Declining populations of less than 250 mature individuals are symptomatic of many Critically Endangered cycads, which, globally, comprise the most threatened group of organisms as a result of collecting and habitat loss. Survival plans focus on law enforcement, reintroduction, and augmentation programmes using plants from the wild and botanical gardens. Augmentation is one of the few remaining options for cycad populations, although the assumed benefits remain untested and there is a possibility that augmentation from different sources could compromise the genetic integrity of existing populations, especially when garden plants have no provenance data. We studied Encephalartos latifrons, a South African endemic, which is a typical Critically Endangered cycad. We studied the extent and structure of genetic diversity in wild and ex situ populations to assess the potential benefits and risks associated with augmentation programmes. We examined 86 plants using amplified fragment length polymorphisms (AFLPs). The 417 AFLP markers thus generated yielded a unique DNA ‘fingerprint’ for each plant. Wild populations retain high levels of genetic diversity and this is reflected among the ex situ holdings at the Kirstenbosch Botanical Garden. No population differentiation is evident, indicating a single panmictic population, consistent with moderately high levels of gene flow between subpopulations and a sexual mode of reproduction. Bayesian clustering identified four genotype groups in the wild, as well as a genotype group only found in ex situ collections. Our results indicate that E. latifrons would benefit from augmentation programmes, including the use of undocumented collections, and careful management of breeding plants would increase the heterogeneity of propagules. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 293–308.     

Genetic uniformity characterizes the invasive spread of water hyacinth (Eichhornia crassipes), a clonal aquatic plant

Aquatic plant invasions are often associated with long‐distance dispersal of vegetative propagules and prolific clonal reproduction. These reproductive features combined with genetic bottlenecks have the potential to severely limit genetic diversity in invasive populations. To investigate this question we conducted a global scale population genetic survey using amplified fragment length polymorphism markers of the world’s most successful aquatic plant invader –Eichhornia crassipes (water hyacinth). We sampled 1140 ramets from 54 populations from the native (South America) and introduced range (Asia, Africa, Europe, North America, Central America and the Caribbean). Although we detected 49 clones, introduced populations exhibited very low genetic diversity and little differentiation compared with those from the native range, and ～80% of introduced populations were composed of a single clone. A widespread clone (‘W’) detected in two Peruvian populations accounted for 70.9% of the individuals sampled and dominated in 74.5% of the introduced populations. However, samples from Bangladesh and Indonesia were composed of different genotypes, implicating multiple introductions to the introduced range. Nine of 47 introduced populations contained clonal diversity suggesting that sexual recruitment occurs in some invasive sites where environmental conditions favour seedling establishment. The global patterns of genetic diversity in E. crassipes likely result from severe genetic bottlenecks during colonization and prolific clonal propagation. The prevalence of the ‘W’ genotype throughout the invasive range may be explained by stochastic sampling, or possibly because of pre‐adaptation of the ‘W’ genotype to tolerate low temperatures.     

Forest refugia revisited: nSSRs and cpDNA sequences support historical isolation in a wide‐spread African tree with high colonization capacity,Milicia excelsa (Moraceae)

The impact of the Pleistocene climate oscillations on the structure of biodiversity in tropical regions remains poorly understood. In this study, the forest refuge theory is examined at the molecular level in Milicia excelsa, a dioecious tree with a continuous range throughout tropical Africa. Eight nuclear microsatellites (nSSRs) and two sequences and one microsatellite from chloroplast DNA (cpDNA) showed a deep divide between samples from Benin and those from Lower Guinea. This suggests that these populations were isolated in separate geographical regions, probably for several glacial cycles of the Pleistocene, and that the nuclear gene pools were not homogenized despite M. excelsa’s wind‐pollination syndrome. The divide could also be related to seed dispersal patterns, which should be largely determined by the migration behaviour of M. excelsa’s main seed disperser, the frugivorous bat Eidolon helvum. Within Lower Guinea, a north–south divide, observed with both marker types despite weak genetic structure (nSSRs: F_ST = 0.035, cpDNA: G_ST = 0.506), suggested the existence of separate Pleistocene refugia in Cameroon and the Gabon/Congo region. We inferred a pollen‐to‐seed dispersal distance ratio of c. 1.8, consistent with wide‐ranging gene dispersal by both wind and bats. Simulations in an Approximate Bayesian Computation framework suggested low nSSR and cpDNA mutation rates, but imprecise estimates of other demographic parameters, probably due to a substantial gene flow between the Lower Guinean gene pools. The decline of genetic diversity detected in some Gabonese populations could be a consequence of the relatively recent establishment of a closed canopy forest, which could negatively affect M. excelsa’s reproductive system.