Consequences of herbivory in the mountain birch (Betula pubescens ssp tortuosa): importance of the functional organization of the tree

Summary Three types of experiments indicate that the functional organization of the mountain birch may influence the ways in which the tree responds to simulated or natural herbivory. The first experiment showed that herbivory to both short and long shoot leaves affects plant development but, because growth largely proceeds by resources of the previous year, is manifested only in the year following the damage. The second experiment showed that even partial damage to a single long shoot leaf caused the axillary bud of that leaf to produce a shorter shoot the next year. Therefore, the value of a leaf depends also on the organ which it is subtending. In the third experiment we manipulated the apical dominance of shoots in ramets and caused improvement to leaf quality in extant shoots. Ramets within a tree responded individually, probably mediated by disturbance of the hormonal control because removal of apical buds elicited the response although removal of the same number of basal buds did not. Induced amelioration is a different response to induced resistance. The two responses are triggered by different cues and may occur in the same plant. By altering hormonal balance of shoots it is potentially possible for herbivores to induce amelioration of food quality. The ways in which herbivory is simulated may explain variability of results obtained when herbivory-induced responses in plants have been studied.     

Impacts of nutrient enrichment and sediment on phytoplankton community structure in the northern Baltic Sea

A three-week mesocosm experiment was conducted in order to study the effects of bottom sediment and nutrient enrichment on phytoplankton and zooplankton community structure in the Archipelago Sea, northern Baltic Sea. The transparent polyethylene enclosures included the whole water column and varied in volume from 30 to 40 m³. There were two types of enclosures: some with natural sediment as a bottom and others with a plastic bottom. The experiment was a 2 × 2 factorial design with presence of sediment and nutrient enrichment as treatment factors. Both the sediment presence and nutrient enrichment significantly increased water nutrient concentrations and the rate of primary production. However, external nutrient enrichment and the presence of sediment stimulated the growth of different phytoplankton groups, indicating that the effect of sediment was not related to nutrient fluxes alone, but involved more complex interactions. External nutrient enrichment was primarily channelled to picoplanktonic cyanobacteria, the biomass of which increased four- to fivefold due to enrichment. The presence of sediment increased the biomass of cryptophytes, chrysophytes and prasinophytes, but decreased the biomass of N₂-fixing cyanobacteria. Zooplankton biomass increased during the experiment, but was not affected by the treatments. The study shows that sediment plays a significant role in phytoplankton dynamics, underlining the importance of including sediment in shallow-water mesocosm experiments. Handling editor: J. Padisak     

Determinants of antagonist binding at the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit, GluR-D. Role of the conserved arginine 507 and glutamate 727 residues.

Previous structural and mutagenesis studies indicate that the invariant alpha-amino and alpha-carboxyl groups of glutamate receptor agonists are engaged in polar interactions with oppositely charged, conserved arginine and glutamate residues in the ligand-binding domain of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. To examine the role of these residues (R507 and E727 in the GluR-D subunit) in the discrimination between agonists and antagonists, we analyzed the ligand-binding properties of homomeric GluR-D and its soluble ligand-binding domain with mutations at these positions. Filter-binding assays using [3H]AMPA, an agonist, and [3H]Ro 48-8587, a high-affinity antagonist, as radioligands revealed that even a conservative mutation at R507 (R507K) resulted in the complete loss of both agonist and antagonist binding. In contrast, a negative charge at position 727 was necessary for agonist binding, whereas the isosteric mutation, E727Q, abolished all agonist binding but retained high-affinity binding for [3H]Ro 48-8587, displaceable by 7,8-dinitroquinoxaline-2,3-dione. Competition binding studies with antagonists representing different structural classes in combination with ligand docking experiments suggest that the role of E727 is antagonist-specific, ranging from no interaction to weak electrostatic interactions involving indirect and direct hydrogen bonding with the antagonist molecule. These results underline the importance of ion pair interaction with E727 for agonist activity and suggest that an interaction with R507, but not with E727, is essential for antagonist binding.     

Flavoprotein hydroxylase PgaE catalyzes two consecutive oxygen-dependent tailoring reactions in angucycline biosynthesis

A simplified model system composed of a NADPH-dependent flavoprotein hydroxylase PgaE and a short-chain alcohol dehydrogenase/reductase (SDR) CabV was used to dissect a multistep angucycline modification redox cascade into several subreactions in vitro. We demonstrate that the two enzymes are sufficient for the conversion of angucycline substrate 2,3-dehydro-UWM6 to gaudimycin C. The flavoenzyme PgaE is shown to be responsible for two consecutive NADPH- and O(2)-dependent reactions, consistent with the enzyme-catalyzed incorporation of oxygen atoms at C-12 and C-12b in gaudimycin C. The two reactions do not significantly overlap, and the second catalytic cycle is initiated only after the original substrate 2,3-dehydro-UWM6 is nearly depleted. This allowed us to isolate the product of the first reaction at limiting NADPH concentrations and allowed the study of the qualitative and kinetic properties of the separated reactions. Dissection of the reaction cascade also allowed us to establish that the SDR reductase CabV catalyzes the final biosynthetic step, which is closely coupled to the second PgaE reaction. In the absence of CabV, the complete PgaE reaction leads invariably to product degradation, whereas in its presence, the reaction yields the final product, gaudimycin C. The result implies that the C-6 ketoreduction step catalyzed by CabV is required for stabilization of a reactive intermediate. The close relationship between PgaE and CabV would explain previous in vivo observations: why the absence of a reductase gene may result in the lack of C-12b-oxygenated species and, vice versa, why all C-12b-oxygenated angucyclines appear to have undergone reduction at position C-6.     

Epigenetic analysis of sporadic and Lynch-associated ovarian cancers reveals histology-specific patterns of DNA methylation

Diagnosis and treatment of epithelial ovarian cancer is challenging due to the poor understanding of the pathogenesis of the disease. Our aim was to investigate epigenetic mechanisms in ovarian tumorigenesis and, especially, whether tumors with different histological subtypes or hereditary background (Lynch syndrome) exhibit differential susceptibility to epigenetic inactivation of growth regulatory genes. Gene candidates for epigenetic regulation were identified from the literature and by expression profiling of ovarian and endometrial cancer cell lines treated with demethylating agents. Thirteen genes were chosen for methylation-specific multiplex ligation-dependent probe amplification assays on 104 (85 sporadic and 19 Lynch syndrome-associated) ovarian carcinomas. Increased methylation (i.e., hypermethylation) of variable degree was characteristic of ovarian carcinomas relative to the corresponding normal tissues, and hypermethylation was consistently more prominent in non-serous than serous tumors for individual genes and gene sets investigated. Lynch syndrome-associated clear cell carcinomas showed the highest frequencies of hypermethylation. Among endometrioid ovarian carcinomas, lower levels of promoter methylation of RSK4, SPARC, and HOXA9 were significantly associated with higher tumor grade; thus, the methylation patterns showed a shift to the direction of high-grade serous tumors. In conclusion, we provide evidence of a frequent epigenetic inactivation of RSK4, SPARC, PROM1, HOXA10, HOXA9, WT1-AS, SFRP2, SFRP5, OPCML, and MIR34B in the development of non-serous ovarian carcinomas of Lynch and sporadic origin, as compared to serous tumors. Our findings shed light on the role of epigenetic mechanisms in ovarian tumorigenesis and identify potential targets for translational applications.     

Variability in the efficacy of delayed inducible resistance in mountain birch

This paper summarizes the results from experiments during 12 years on effects of delayed inducible resistance of mountain birches (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) on performance of a geometrid, Epirrita autumnata (Bkh.). Manual defoliation usually reduced significantly pupal mass of E. autumnata the next summer. The years interacted significantly with the defoliation treatment indicating variation among years in the responses of trees of larvae, or that the methodological differences between different experiments may have affected the results. Potential methodological sources for the annual variability were discussed and found unlikely. In addition, the efficacy of defoliation treatment in reducing the pupal mass was greatest when foliage quality in control trees was best, suggesting a contribution of biological causes to the annual variability.     

Early-onset renal cell carcinoma as a novel extraparaganglial component of SDHB-associated heritable paraganglioma

Hereditary paraganglioma syndrome has recently been shown to be caused by germline heterozygous mutations in three (SDHB, SDHC, and SDHD) of the four genes that encode mitochondrial succinate dehydrogenase. Extraparaganglial component neoplasias have never been previously documented. In a population-based registry of symptomatic presentations of phaeochromocytoma/paraganglioma comprising 352 registrants, among whom 16 unrelated registrants were SDHB mutation positive, one family with germline SDHB mutation c.847-50delTCTC had two members with renal cell carcinoma (RCC), of solid histology, at ages 24 and 26 years. Both also had paraganglioma. A registry of early-onset RCCs revealed a family comprising a son with clear-cell RCC and his mother with a cardiac tumor, both with the germline SDHB R27X mutation. The cardiac tumor proved to be a paraganglioma. All RCCs showed loss of the remaining wild-type allele. Our observations suggest that germline SDHB mutations can predispose to early-onset kidney cancers in addition to paragangliomas and carry implications for medical surveillance.     

Fallout from Chernobyl and incidence of childhood leukaemia in Finland, 1976-92.

OBJECTIVE--To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland. DESIGN--Nationwide cohort study. External exposure measured for 455 Finnish municipalities with instruments driven 19,000 km throughout the country. Values specific to municipalities corrected for shielding due to houses and fallout from A bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children. Mean effective dose for two years after incident calculated from these measurements. Data on childhood leukaemia obtained from Finnish cancer registry and verified through hospitals treating childhood cancers. SETTING--Finland, one of the countries most heavily contaminated by the Chernobyl accident; the population was divided into fifths by exposure. SUBJECTS--Children aged 0-14 years in 1976-92. MAIN OUTCOME MEASURES--Standardised incidence ratio of childhood leukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for three periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fifths for each period. RESULTS--Population weighted mean effective doses for first two years after the accident were 410 microSv for the whole country and 970 microSv for the population fifth with the highest dose. In all Finland the incidence of childhood leukaemia did not increase 1976-92. The relative excess risk 1989-92 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%). CONCLUSIONS--An important increase in childhood leukaemia can be excluded. Any effect is smaller than eight extra cases per million children per year in Finland. The results are consistent with the magnitude of effect expected.     

Effect of nutrient enrichment on bacterioplankton biomass and community composition in mesocosms in the Archipelago Sea, northern Baltic

Effects of nutrient enrichment on the biomass and communitycomposition of heterotrophic bacteria and picocyanobacteriawere studied in large (42 m³) mesocosms in the brackish-waterArchipelago Sea (Baltic Sea) in late summer 2000 using cellcounts and denaturing gradient gel electrophoresis (DGGE) ofpolymerase chain reaction (PCR)-amplified 16S rRNA gene fragments.The identity of the major DNA bands was determined by sequencing.The obtained sequences were related to - and -proteobacteria,actinobacteria, verrucomicrobia and cyanobacteria. Nitrogenand phosphorus additions increased the biomasses of heterotrophicbacteria and picocyanobacteria and caused significant changesin their community composition judging from the DGGE bandingpatterns. Most verrucomicrobial bands had their highest relativeintensity in the control treatment and their lowest in the highernutrient addition treatment, whereas most Synechococcus-relatedbands had their lowest relative intensity in the lower nutrientaddition treatment. The responses of proteobacteria and actinobacteriawere more variable. The presence of both freshwater and marinesequences among the closest relatives to our sequences highlightsthe intermediate character of the Archipelago Sea between afreshwater and truly marine environment.