Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

Circular and linear DNA molecules in the Entamoeba histolytica complex molecular karyotype

Entamoeba histolytica genome was analysed by pulsed field gel electrophoresis under conditions to separate linear chromosomes in the 170–1400 kb range. We identified linear DNA molecules of 227, 366, 631, 850, 1112 and 1361 kb (mean sizes obtained by three different methods) and we estimated their reorientation times and migration velocities at various experimental conditions. DNA shift mobility assays, using ethidium bromide, suggested that bands migrating at 227 and 631 kb contain linear and circular DNA, whereas a band at 436 kb has only circular DNA. We obtained a regression equation relating sizes of supercoiled DNA molecules with their migration velocities during a pulse at constant electric field and temperature. We also developed a computer program (EHPATTERNS) that predicts the migration per pulse and the resolution order of circular and linear E. histolytica DNA at different pulse times and constant driving and frictional forces. The simulation showed that linear DNA molecules frequently co-migrate with circular molecules, but circular molecules change when the pulse time varies. This molecular mixture generates broad bands and difficulties in the interpretation of the molecular karyotype of E. histolytica. Received: 19 January 1999 / Revised version: 3 November 1999 / Accepted: 22 November 1999     

Seasonal mortality trends in tree‐feeding insects: a field experiment

Abstract 1. The majority of general life‐history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For herbivorous insects, seasonal differences in food quality are reasonably well described, but seasonal dynamics of top‐down selective forces are poorly documented. 2. The present study attempted to quantify seasonal changes in predation risk of folivorous insect larvae in temperate forest habitats. In a series of field experiments, artificial larvae were exposed to predators, and the resulting bird‐inflicted damage was recorded. The trials were repeated regularly throughout the course of two summers. 3. A distinct peak of larval mortality was recorded in mid‐June (the nestling period for most insectivorous passerine birds), after which predation risk declined to a plateau of 20–30% below the peak value. 4. The recorded pattern is interpreted as a consequence of seasonal changes in the number and behaviour of insectivorous birds, and the abundance of alternative food resources for these predators. 5. A quantitative analysis based on field data indicated that considering temporal variation in mortality in life‐history models is crucial for obtaining realistic predictions concerning central life‐history traits, such as final body size in different generations.     

Genotypic and phenotypic variation of Lewis antigen expression in geographically diverse Helicobacter pylori isolates

Background: Helicobacter pylori are a persistent colonizer of the human gastric mucosa, which can lead to the development of peptic ulcer disease and gastric adenocarcinomas. However, H. pylori can asymptomatically colonize a host for years. One factor that has been hypothesized to contribute to such persistence is the production of Lewis (Le) antigens in the lipopolysaccharide layer of the bacterial outer membrane as a form of molecular mimicry, because humans also express these antigens on their gastric mucosa. Humans and H. pylori both are polymorphic for Le expression, which is driven in H. pylori by variation at the Le synthesis loci. In this report, we sought to characterize Le genotypic and phenotypic variation in geographically diverse H. pylori isolates. Materials and Methods: From patients undergoing endoscopy in 29 countries, we determined Le phenotypes of 78 H. pylori strains and performed genotyping of the galT and β‐(1,3)galT loci in 113 H. pylori strains. Results: Le antigen phenotyping revealed a significant (p < .0001) association between type 1 (Le^a and Le^b) expression and strains of East Asian origin. Genotyping revealed a significant correlation between strain origin and the size of the promoter region upstream of the Le synthesis gene, galT (p < .0001). Conclusion: These results indicate that the heterogeneity of human Le phenotypes is reflected in their H. pylori colonizing strains and suggest new loci that can be studied to assess the variation of Le expression.     

Helicobacter pylori and the birth cohort effect: evidence for stabilized colonization rates in childhood

Background: The prevalence of Helicobacter pylori has declined over recent decades in developed countries. The increasing prevalence with age is largely because of a birth cohort effect. We previously observed a decline in H. pylori prevalence in 6‐ to 8‐year‐old Dutch children from 19% in 1978 to 9% in 1993. Knowledge about birth‐cohort‐related H. pylori prevalence is relevant as a predictor for the future incidence of H. pylori‐associated conditions. Aim: The aim of this study was to investigate whether the birth cohort effect of H. pylori observed between 1978 and 1993 continued in subsequent years. Methods: Anti‐H. pylori IgG antibodies and anti‐CagA IgG antibodies were determined in serum samples obtained in 2005/2006 from 545 Dutch children aged 7–9 years who participated in the Prevention and Incidence of Asthma and Mite Allergy birth cohort. The H. pylori and CagA antibodies were determined by enzyme‐linked immunosorbent assays that have been extensively validated in children, with a 94% sensitivity for H. pylori colonization and a 92.5% sensitivity for colonization with a cagA‐positive strain. Results: Of the 545 children (M/F 300/245), most (91.5%) were of Dutch descent. The H. pylori positivity rate was 9% (95% CI 6.6–11.4%). The prevalence of CagA antibodies was 0.9% (95% CI 0.1–1.6%). No significant differences were demonstrated in H. pylori and cagA prevalence in relation to gender or ethnicity. Conclusion: The prevalence of H. pylori in childhood has remained stable in the Netherlands from 1993 to 2005, suggesting a stabilization of the previously decreasing trend in subsequent birth cohorts. This finding may reflect stabilization in determinants such as family size, housing, and hygienic conditions (or offset by day care). If confirmed in other populations in developed countries, it implies that colonization with H. pylori will remain common in the coming decades. Remarkably however, the rate of colonization with cagA⁺H. pylori strains has become very low, consistent with prior observations that cagA⁺ strains are disappearing in Western countries.     

The RETINOBLASTOMA-RELATED gene regulates stem cell maintenance in Arabidopsis roots

The maintenance of stem cells in defined locations is crucial for all multicellular organisms. Although intrinsic factors and signals for stem cell fate have been identified in several species, it has remained unclear how these connect to the ability to reenter the cell cycle that is one of the defining properties of stem cells. We show that local reduction of expression of the RETINOBLASTOMA-RELATED (RBR) gene in Arabidopsis roots increases the amount of stem cells without affecting cell cycle duration in mitotically active cells. Conversely, induced RBR overexpression dissipates stem cells prior to arresting other mitotic cells. Overexpression of D cyclins, KIP-related proteins, and E2F factors also affects root stem cell pool size, and genetic interactions suggest that these factors function in a canonical RBR pathway to regulate somatic stem cells. Expression analysis and genetic interactions position RBR-mediated regulation of the stem cell state downstream of the patterning gene SCARECROW.     

Prevalence of Helicobacter pylori in Georgian patients with dyspepsia

BACKGROUND: Georgia has showed a high prevalence of peptic ulcer disease (PUD), but the prevalence of Helicobacter pylori in this country is practically unknown. The purpose of this study was to determine the prevalence of H. pylori and specific genotypes in different populations in Georgia. MATERIALS AND METHODS: We studied 62 patients from several hospitals in Tbilisi, Georgia. More than 55% of patients had PUD. We determined H. pylori presence as well as specific genotypes cagA and vacA by polymerase chain reaction. In addition, we studied serum samples from 94 healthy persons to determine H. pylori and CagA prevalence by ELISA. RESULTS: We found a high prevalence of H. pylori and CagA in the healthy population (70.2 and 57.4%, respectively) and a high prevalence of CagA among the H. pylori-positive persons (71.2%). Prevalence increased with age as reported in other countries (p = .05). Among symptomatic persons, we found nearly the same high prevalence of H. pylori (64.5%) as in the asymptomatic population. Furthermore, in symptomatic H. pylori patients, we found 65.0 and 67.5% prevalence of cagA and vacA, respectively. For 33 patients with PUD, 24 patients (72.7%) were H. pylori positive and 66.7% of them were cagA positive. In contrast, among the patients with non-ulcer dyspepsia (NUD), 16 (55.2%) were H. pylori positive and 62.5% of them were colonized with cagA-positive strains. H. pylori and cagA prevalence were not significantly different between PUD and patients with NUD. CONCLUSIONS: We confirmed that among individuals in Georgia, the prevalence of H. pylori is high and cagA-positive strains were equally present among H. pylori-positive patients with PUD and NUD and asymptomatic persons.     

The impact of Helicobacter pylori on atopic disorders in childhood

Background: The prevalence of Helicobacter pylori in Western populations has steadily decreased. This has been suggested as one of the factors involved in the recent increase of asthma and allergy. Some studies have reported a negative association between H. pylori and asthma and allergy, but data are inconsistent and there are a few studies in children. Aim: We investigated whether the prevalence of H. pylori was associated with asthma symptoms, allergic rhinitis, and atopic dermatitis in childhood. Methods: We determined IgG anti‐H. pylori and CagA antibodies in serum of Dutch children, who took part in the PIAMA birth cohort study. Serum was collected from 545 children, aged 7–9 years (Dutch ethnicity 91.5%). Symptoms of asthma and atopy were assessed by yearly questionnaires. Chi‐square tests and logistic regression were used. Results: We found 9%H. pylori and 0.9% CagA seropositivity. Twelve (5.9%) children with reported wheezing ever were H. pylori positive, compared to 37 (10.9%) of the non‐wheezers (p = .05). No significant differences in H. pylori prevalence were found between children with or without allergic rhinitis (8.5% vs 9.5%), atopic dermatitis (8.7% vs 9.2%), and physician‐diagnosed asthma (7.1% vs 9.4%). Multivariate analysis showed no significant associations between H. pylori seropositivity and wheezing (OR 0.52; 95% CI 0.25–1.06), allergic rhinitis (OR 0.96; 95% CI 0.51–1.81), atopic dermatitis (OR 1.05; 95% CI 0.56–1.98) or physician‐diagnosed asthma (OR 0.87; 95% CI 0.37–2.08). Conclusion: We found a borderline significantly lower H. pylori seropositivity in children with wheezing compared to non‐wheezers, but no association between H. pylori serum‐antibody status and allergic rhinitis, atopic dermatitis, or asthma.