Comparative habitat susceptibility to invasion by Chinese ash (<Emphasis Type="Italic">Fraxinus chinensis</Emphasis>: Oleaceae) in a tropical Andean landscape

Chinese ash (Fraxinus chinensis) is an exotic tree species that has been used in non-commercial monospecific plantations for revegetation programs in the Central Andes of Colombia. At the Otún river watershed, these plantations occur in patches intermixed with old pastures, oak forests, and successional forests. In this heterogeneous landscape, the ash has been able to invade some of its surrounding habitats. This study evaluates the invasion patterns of ash to each of these habitats and experimentally quantifies seed and seedling survivorship and seedling growth as three processes that could determine ash establishment. Of the four habitats examined, old pastures were the most vulnerable to invasion, followed by oak plantations, and successional forest. Ash plantations exhibited recruitment levels intermediate between pastures and oak plantations. Abandoned pastures showed the highest seed germination, seedling survivorship, and seedling growth. In the ash plantations, recruitment seemed negatively affected by the low number of germinated seeds, high mortality of seedlings, and low growth. Invasion in oak plantations was constrained by high seed mortality and burial of seedlings by leaf litter, although the seedlings that did survive grew fast and produced a high number of leaves. Within the successional forest, Chinese ash seeds germinated but establishment was constrained by a reduced seedling survivorship and low growth. This research offers new evidence of how different processes affecting the establishment of an invader may differ among landscape elements, and it also yields important information for the management and control of ash in these Andean landscapes.     

Biological characteristics of an invasive south African species

Senecio inaequidens, a south African species that has recently invaded parts of Europe, especially human disturbed habitats, was examined under laboratory and glasshouse conditions to assess the germination of achenes, soil seed banks, growth of seedlings and its breeding system. These observations allowed identification of ecological characteristics that may contribute to the invasiveness of the species. Achenes derived from three populations of S. inaequidens were germinated over a wide temperature range (from 14/6 °C day/night temperatures to a constant temperature of 30 °C). They exhibited a rapid achene germination especially when temperatures reached 20 °C. Germination of seeds from soil samples also exhibited a prolonged germination over time suggesting therefore different types of dormancy. Growth response was studied along a nitrogen gradient from 0.33 to 16.0 mmol l^–1 and data were interpreted using growth analysis. Seedlings of S. inaequidens exhibited a slow growth in low nutrient availability and a rapid growth rate when exposed to high nutrient availability, which contributed to producing a large leaf area and biomass. Four types of pollination were studied in S. inaequidens. Hand-pollinations showed that S. inaequidens was mostly self-incompatible. Self-pollinated capitula only showed 7.6% viable achenes, significantly lower than insect-pollinated and cross-pollinated capitula. Some individuals were more self-fertile than others ensuring the production of some offspring in a situation of colonisation. Natural pollination occurred with generalist insects. Most of these results confirm the invasive ability of S. inaequidens.     

Inhibition of invasiveness of human lung cancer cell line H1299 by over-expression of cofilin

The Rho-LIM-kinase (LIMK) signaling pathway, believed to be involved in the regulation of tumor invasion, specifically regulates the activity of cofilin. However, it is unclear whether cofilin plays a pivotal role in tumor invasiveness. In this paper we show using a tet-on gene expression system that over-expression of cofilin inhibits the invasiveness of human lung cancer H1299 cells. Over-expressed cofilin disrupts the actin cytoskeleton at the leading edge of the cell and up-regulates p27(kip1), which is known to be involved in regulating cell motility. Removal of cofilin over-expression normalizes the p27(kip1) level and concomitantly restores the invasiveness of the cultured cells. These findings suggest that excessive cofilin production might prevent cancer cell invasion.     

Growth and competition between seedlings of an invasive plantation tree, <Emphasis Type="Italic">Acacia mangium,</Emphasis> and those of a native Borneo heath-forest species, <Emphasis Type="Italic">Melastoma beccarianum</Emphasis>

An introduced plantation tree species, Acacia mangium Willd., is becoming invasive in the Brunei region of Borneo. To examine its invasive potential, a greenhouse, additive series experiment (target–neighbour) involving seedlings of A. mangium and those of a common native heath-forest (kerangas), Melastoma beccarianum Cogn. was carried out under low and high light regimes in intra- and interspecific combinations over a 6-month period. Significant variations in growth parameters (other than biomass allocation patterns) existed amongst seedlings from different treatments. A major part of this variation in growth could be attributed to the main factors of target species, neighbour species, and competition (seedling density). For the growth variables examined, the target–species response was not consistent across light regimes. Under high light conditions, Acacia was the better competitor; the Lotka-Volterra competition coefficient effect of Melastoma on Acacia was lower (=0.30) than the effect of Acacia on Melastoma (=0.54). However, the reverse occurred under low light conditions with Melastoma gaining the upper hand (=1.45 and =0.44). These results show that light (and hence disturbance) can strongly influence the pattern and intensity of both intra- and interspecific competition between invasive and local flora species. Relatively intact forest is unlikely to be invaded by Acacia trees (as they are poor competitors under this scenario). On the other hand, the Acacia trees can easily invade disturbed forests, especially those prone to recurring drought and fire, and over time convert the habitats to nearly monospecific stands, as is presently being observed in Brunei.     

Invasion genetics of the Eurasian spiny waterflea: evidence for bottlenecks and gene flow using microsatellites

The Eurasian spiny waterflea (Bythotrephes longimanus) is a predacious zooplankter that has increased its range in Europe and is rapidly invading inland water-bodies throughout North America's Great Lakes region. To examine the genetics of these invasions, we isolated five microsatellite DNA loci with between 5 and 19 alleles per locus. We sampled three populations where B. longimanus has been historically present (Switzerland, Italy, and Finland) as well as an introduced European population (the Netherlands) and three North American populations (Lakes Erie, Superior, Shebandowan). Consistent with a bottleneck during colonization (i.e. founder effect), average heterozygosities of the four European populations ranged from 0.310 to 0.599, and were higher than that of three North American populations (0.151-0.220). Pairwise F(ST) estimates among North American populations (0.002-0.063) were not significantly different from zero and were much lower than among European populations (0.208-0.474). This is consistent with a scenario of high gene flow among North American populations relative to that of European ones. Contrary to an invasion bottleneck, however, Erie and Superior populations contained similar numbers of rare alleles as European populations. Assignment tests identified several migrant genotypes in all introduced populations (the Netherlands, Erie, Superior, Shebandowan), but rarely in native ones (Switzerland, Italy and Finland). A large number of genotypes from North America were assigned to our Italian population suggesting a second, previously unidentified, invasion source somewhere in the region of northern Italy. Together, our results support an invasion bottleneck for North American populations that has been largely offset by gene flow from multiple native sources, as well as gene flow among introduced populations.     

Arsenic trioxide (As2O3) inhibits invasion of HT1080 human fibrosarcoma cells: role of nuclear factor-kappaB and reactive oxygen species

In order to define the role of As2O3 in regulating the tumor cell invasiveness, the effects of As2O3 on secretion of matrix metalloproteinases (MMPs) and urokinase plasminogen activator (uPA), and in vitro invasion of HT1080 human fibrosarcoma cells were examined. As2O3 inhibited cell adhesion to the collagen matrix in a concentration dependent manner, whereas the same treatment enhanced cell to cell interaction. In addition, As2O3 inhibited migration and invasion of HT1080 cells stimulated with phorbol 12-myristate 13-aceate (PMA), and suppressed the expression of MMP-2, -9, membrane type-1 MMP, uPA, and uPA receptor (uPAR). In contrast, As2O3 increased the expression of tissue inhibitor of metalloproteinase (TIMP)-1 and PA inhibitor (PAI)-1, and reduced the MMP-2, -9, and uPA promoter activity in the presence and absence of PMA. Furthermore, the promoter stimulating and DNA binding activity of nuclear factor-kappaB (NF-kappaB) was blocked by As2O3, whereas the activator protein-1 activity was unchanged. Pretreatment of the cells with N-acetyl-L-cysteine (NAC) significantly prevented suppression of MMPs and uPA secretion, DNA binding activity of NF-kappaB, and in vitro invasion of HT1080 cells by As2O3, suggesting a role of reactive oxygen species (ROS) in this process. These results suggest that As2O3 inhibits tumor cell invasion by modulating the MMPs/TIMPs and uPA/uPAR/PAI systems of extracellular matrix (ECM) degradation. In addition, the generation of ROS and subsequent suppression of NF-kappaB activity by As2O3 might partly be responsible for the phenomena. Overall, As2O3 shows potent activity controlling tumor cell invasiveness in vitro.     

Genetic analysis of natural hybrids between endemic and alien Rubus (Rosaceae) species in Hawai`i

A population of putative hybrids between theendemic Rubus hawaiensis and naturalizedR. rosifolius was discovered inKpahulu Valley, on the island of Maui inthe Hawaiian archipelago. The goal of thisstudy was to molecularly characterize thisnatural hybridization event, investigate themode of hybridization, and determine the malefertility of the hybrid individuals. Bothmorphological and RAPD marker data indicatethat the putative hybrid individuals are theprogeny of R. rosifolius and R.hawaiensis. All 39 hybrid individuals sampledhad the chloroplast DNA haplotype of R.rosifolius. Thus hybridization appears to beasymmetric, with R. rosifolius acting asthe maternal parent. All hybrid individualsassessed for pollen stainability were sterile,and there was no evidence of backcrossing toeither parent. This result suggests thathybrids are of the first filial generation andthat variation among hybrids reflectsdifferences within the parental populations.Sympatric populations of R. hawaiensisand R. rosifolius occur on four islandsand six additional alien species of Rubusare naturalized and sympatric with R. hawaiensisin Hawai`i. Further investigationis merited to assess whether hybridization maypose a threat to the long term viability ofR. hawaiensis. This study highlights theincreasing frequency and negative consequencesof native-alien hybridization and theimportance of maintaining active alien speciescontrol programs in the Hawaiian Islands.     

羊栖菜多糖诱导HL-60细胞凋亡的研究

用MTT法观察羊栖菜多糖(SFPS)在体外抗人白血病HL-60细胞增殖作用;扫描电镜、透射电镜、DNA电泳和流式细胞仪检测HL-60细胞凋亡。结果表明SFPS对HL-60细胞具有显著生长抑制作用,并呈量效和时效关系,药物作用24,36,48,72h的IC_(50)分别为390,362,402,421mg/L;药物浓度为300mg/L和500mg/L作用HL-60细胞后,琼脂糖凝胶电泳显示有凋亡细胞特有的DNA梯状条带,细胞微绒毛减少、染色质固缩、过集,凋亡小体形成;DNA直方图出现亚G_1峰。在一定浓度范围内,SFPS诱导细胞凋亡的作用呈现浓度和时间依赖性,同时G_2/M期细胞比例增多。因此,SFPS抗肿瘤作用与诱导细胞凋亡和G_2/M期细胞阻滞有关。     

Colonization of hydrophilic contact lenses by yeast

The growth of six strains of yeast was analyzed in vitro in order to assess their capacity for colonizing (adhesion and invasion) hydrophilic contact lenses. Lenses with different water content were cultured in two culture media for 3, 7, 14, and 21 days. Only strain 93150 of Candida albicans could adhere to and invade the polymers. Specifically, fungal growth was observed in cultures with Sabourauds broth. The degree of yeast colonization of contact lenses was significantly related to the species, the strain, and the culture medium in which the yeast and lenses were cultured. The results here obtained were compared with those reported for the filamentous fungus Aspergillus niger 2700. For both microorganisms, the strain and the medium in which the lenses and microorganism were cultured influenced the colonization, but the percentage of colonized lenses, the degree of colonization, and the density and size of the internalized colonies were always noticeably lower for C. albicans 93150. Colonization by A. niger 2700 was also related to the type of material of the lenses and the incubation period. For both microorganisms, when the strain is right and the growth and development are correct, colonization of hydrophilic contact lenses occurs.