Light and ethylene effects on assimilate distribution,acid invertase activity and keeping quality of begonia

Flowering plants of Begonia × cheimantha cv Emma and Begonia x hiemalis cv Schwabenland Red were exposed to different light levels (0, 40, 80 M m^–2S^–1) and to ethylene (150 nl 1^–1) in growth cabinets. Increasing irradiance level increased the number of flower buds in both begonia species. The amount of ¹⁴C-assimilates translocated to flower buds and the acid invertase activity in flower buds and flowers also increased with increasing irradiance level. Conversely, treatment with ethylene decreased the accumulation of ¹⁴C in flowers and flower buds, but did not affect acid invertase activity. Ethylene accelerated abscission of flowers and flower buds and increased the number of cup shaped and small flowers.     

Sequence of the gene encoding the 16S rRNA of the beer spoilage organismMegasphaera cerevisiae

The 16S ribosomal RNA gene from the beer-spoilage organism,Megasphaera cerevisiae was polymerase chain reaction (PCR)-amplified and sequenced. Analysis confirmed the phylogenetic position ofM. cerevisiae as a sister taxon ofMegasphaera elsdenii, within the obligately anaerobic, Gram-negative cocci. The sequence obtained should facilitate the development of DNA probes for early detection of this spoilage organism.     

Identity, beer spoiling and biofilm forming potential of yeasts from beer bottling plant associated biofilms

Wild yeasts were isolated from process surfaces of two breweries. In total, 41 strains were obtained and differentiated by cultivation on CuSO₄ or crystal violet containing selective media, by fatty acid profiling and by a restriction analysis of the region spanning the internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene. The restriction analysis showed the highest differentiating capacity and resulted in eleven groups. These groups were identified by the API ID 32 C kit or by sequencing the D1/D2 region of the 26S rRNA gene. Most of the wild yeasts were identified as Saccharomyces cerevisiae (46% of all isolates) and Candida pelliculosa (anamorph: Pichia anomala) (24%). No obvious differences were detected between the two breweries. While all of the S. cerevisiae isolates were able to grow in beer, only six out of 10 C. pelliculosa strains were able to tolerate this substrate. However, most of the C. pelliculosa strains showed biofilm formation in a microplate assay, but none of the S. cerevisiae isolates. Therefore, it is assumed that the former species is involved in attachment and primary biofilm formation on beer bottling plants, while S. cerevisiae is a late colonizer of a preformed biofilm but increased the beer spoiling potential of the biofilm.     

Continuous production of non-alcohol beer by immobilized yeast at low temperature

Summary A system for production of non-alcohol beer is described. A limited fermentation is carried out with immobilized cells ofSaccharomyces cerevisiae in a packed bed reactor. In the reactor, combined stress factors such as low temperature (2–4°C) and anaerobic conditions limit cell metabolism. Of the available sugars only a small amount of glucose is metabolized, resulting in low concentrations of ethanol (<0.08%). The absence of oxygen affects the redox balance of the yeast cell, and thus stimulates formation of esters and higher alcohols. Products are formed by reduction of wort aldehydes, as well as reduction of intracellular metabolites. Despite the stress conditions, biomass increases during prolonged production periods. In batch experiments,S. cerevisiae strain W34 grows at low temperatures and a mininum growth temperature of –2 °C was found, indicating that a further reduction of temperature during production will not inhibit growth. The characteristics of the system allow its use in very different applications. Potential applications of the immobilized system are discussed.This paper is dedicated to Professor Herman Jan Phaff in honor of his 50 years of active research which still continues.     

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.     

Food quality effects on life history traits and fitness in the generalist herbivore Daphnia

Summary Life table experiments were conducted on the generalist suspension feeder Daphnia galeata, using as food the two green algae (Chlorophyta) Scenedesmus acutus and Oocystis lacustris. Oocystis was hypothesized to be a lower quality food because it is convered with a thick sheath, believed to reduce digestibility. Results showed that Oocystis is a lower quality food for Daphnia, but only at relatively low food concentrations (0.15 mg C/L) and not at higher concentrations (1.0 mg C/L). At 0.15 mg C/L, Daphnia intrinsic rate of increase (r) when grown on Oocystis was only half that when grown on Scenedesmus. Daphnia r was similar at 0.15 mg C/L Oocystis and 0.075 mg C/L Scenedesmus, indicating that Daphnia requires twice as much Oocystis as Scenedesmus to achieve the same fitness. Intrinsic rate of increase was lower on Oocystis mainly because age at first reproduction was greatly delayed compared to that on Scenedesmus (13.6 vs 7.3 d). In addition, juvenile growth and survivorship were reduced on Oocystis compared with Scenedesmus. Clutch sizes were similar on the two foods, indicating that once individuals reached adulthood, the two foods were similar in quality. In contrast, at high food concentrations (1.0 mg C/L), the two algae were similar in quality for both juveniles and adults, and r was not significantly different on the two foods. Ingestion and assimilation rate experiments whowed that Daphnia consumes the two algae at identical rates, and that adults assimilate the two algae at similar rates. However, juveniles assimilate Oocystis at much lower rates than Scenedesmus, possibly accounting for reduced juvenile growth and delay in age at maturity at low concentrations. Thus, Daphnia exhibits an ontogenetic shift in its ability to utilize Oocystis, and this can result in juvenile bottlenecks in which survival and growth of young age classes are of critical importance in determining population dynamics. Because food quality effects were manifested primarily in juveniles and at low concentrations, food quality effects in nature will depend on phytoplankton abundance and age-structure of Daphnia populations.     

Biomass-dependent effects of common carp on water quality in shallow ponds

We examined the biomass-dependent effects of common carp (Cyprinus carpio) on water quality in 10 ponds at the Eagle Mountain Fish Hatchery, Fort Worth, Texas, USA. Ponds contained 0–465 kg ha⁻¹ of common carp. We measured limnological variables at weekly intervals for four weeks in early summer, after which ponds were drained and the biomass of fish and macrophytes was determined. Common carp biomass was significantly positively correlated with chlorophyll a, total phosphorus, total nitrogen, and Keratella spp. density and negatively correlated to bushy pondweed (Najas guadalupensis) biomass. In addition, we combined our data with data from comparable studies to develop more robust regression models that predict the biomass-dependent effects of common carp on water quality variables across a wide range of systems.     

Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Landscape context outweighs local habitat quality in its effects on herbivore dispersal and distribution

Past studies with spatially structured herbivore populations have emphasized the primacy of intrinsic factors (e.g., patch quality), patch geometry (e.g., patch size and isolation), and more recently landscape context (e.g., matrix composition) in affecting local population abundance and dispersal rate. However, few studies have examined the relative importance of each factor, or how they might interact to affect herbivore abundance or dispersal. Here, we performed a factorial field experiment to examine the independent and interactive effects of patch quality (plant biomass, leaf protein, leaf phenolics) and matrix composition [mudflat or non-host grass (Bromus inermis)] on planthopper (Prokelisia crocea) emigration from host-plant patches (prairie cordgrass, Spartina pectinata). In addition, a field survey was conducted to examine the relative importance of patch quality, geography, and matrix composition on planthopper occupancy and density. In the experiment, we found that rates of emigration from low and intermediate quality patches were, on average, 21% percent higher for patches embedded in brome than mudflat. In contrast, the emigration rate was unaffected by matrix composition in nutrient-rich patches. Within matrix types, plant quality had little effect on emigration. In the survey, planthopper density and the patch occupancy rate of planthoppers increased nonadditively with increasing patch size and the percentage of the surrounding matrix composed of mudflat. This study suggests that landscape-level factors, such as the matrix, may be more important than factors intrinsic to the patches.     

Zooplankton and their relationships with water quality and fisheries

Zooplankton population structure in Rutland Water changed over the first five years of the reservoir's existence. Daphnia pulex, initially dominant was replaced by D. hyalina in late 1975 and since 1979 this latter cladoceran has coexisted for part of each year with Bosmina longirostris. Population fluctuations of all the main crustacean zooplankton — D. hyalina, Cyclops spp. and Diaptomus gracilis — were erratic in the first three years (1975–1977) but have since become more regular. The relationships of the zooplankton with their potential algal food supply and with their potential predators, the fish population, are discussed.     

The occurrence of flowering and fruiting on individual trees over 3 years and their effects on subsequent crown condition

Summary The level of fruiting in four forest trees species (Picea sitchensis, P. abies, Pinus sylvestris and Fagus sylvatica) was monitored in Great Britain over the period 1989–1991. In addition, assessments of crown transparency were available for many of the trees for 1987 and 1988. The monitoring period encompassed severe summer droughts in 1989 and 1990, with wetter conditions in 1991. Variations in the level of fruiting in spruce and beech (Fagus sylvatica L.) were seen, with a marked peak in 1990. No pattern was apparent in Scots pine (Pinus sylvestris L.). Coning, which was greater in trees with the least transparent crowns, had no discernible effect on the crown transparency of the conifers. Cupule production in beech was greatest in trees with the most transparent crowns, and trees with high numbers of cupules in 1990 tended to have greater crown dieback recorded in 1991.     

Characteristics of a rice beer (zutho) and a yeast isolated from the fermented product in Nagaland,India

Rice beer, known locally as zutho was collected in the Kohima district in Nagaland, India, and subjected to analytical and microbiological characterization. Zutho was a whitish porridge-like slurry containing 5.0% (v/v) ethanol. Volatile esters and higher alcohols, such as ethyl acetate and 3-methylbutanol, were detected in this indigenous alcoholic beverage by gas chromatography. The pH and acidity of zutho were 3.6 and 5.1, respectively. Zutho had a fruity aroma and sour taste and its unique aroma had characteristics similar to those of Japanese sake and sprouted rice sake. A fermentation yeast isolated from zutho was identified as being a strain of Saccharomyces cerevisiae and was found to be suitable as the brewing yeast for ethanol fermentation.     

The effects of phosphorus nutrition and soil pH on the growth of some ancient woodland indicator plants and their interaction with competitor species

The forest under-storey herbs Anemone nemorosa, Lamiastrum galeobdolon and Veronica montana are generally considered indicator species of old, broadleaved woodland sites where the soil fertility is often low. In a glasshouse bioassay, however, all three species not only showed large positive growth responses to supplied P concentrations (0–10mgL ^–1) solutions, but also tolerated high P concentrations (20–40mgL ^–1), well above those normally found in their natural habitat. Plants responded by raising the concentrations of P in their shoot and root tissues and increasing their biomass, resulting in an increased P uptake. A shade-tolerant competitor species, Urtica dioica, also grew vigorously across the full range of P concentrations, restricting the growth of the woodland species. This emphasises the difficulty of establishing semi-natural woodland vegetation in the presence of competitor species, for example in situations where new woodlands are planted on fertile ex-agricultural soils containing large residual concentrations of P. The influence of soil pH on the growth and nutrient relations of A. nemorosa, L. galeobdolon, V. montana, Poa trivialisandU. dioicawas determined in a separate experiment using an ex-arable soil as the growing medium with pH levels adjusted from 7.4 to 5.8 and 4.3 respectively. Acidifying the soil enhanced growth, but reduced the concentrations of N, P and K in the leaves of all three woodland species, probably due to dilution of these minerals in the increased dry matter production. The competitor species (P. trivialis and U. dioica) responded in similar manner to the woodland indicator species. These results suggest that manipulating soil pH as a means of facilitating the establishment of woodland indicator species in new farm woods is unlikely, in the short term, to be effective where competitor species are present.     

Fumonisins: Isolation,chemical characterization and biological effects

The fumonisin B mycotoxins (FB₁ and FB₂) have been purified and characterized from corn cultures of Fusarium moniliforme strain MRC 826. Fumonisin B₁ (FB₁, the major fumonisin produced in culture, has been shown to be responsible for the major toxicological effects of the fungus in rats, horses and pigs. Recent investigations on the purification of compounds with chromatographic characteristics similar to FB₁ have led to the identification of two new fumonisins, FB₃ and FB₄. Fumonisins A₁ and A₂, the N-acetyl derivatives of FB₁ and FB₂ respectively, were also purified and shown to be secondary metabolites of the fungus. Short-term carcinogenesis studies in a rat liver bioassay indicated that over a period of 15 to 20 days, at dietary levels of 0.05–0.1%, FB₂ and FB₃ closely mimic the toxicological and cancer initiating activity of FB₁ and thus could contribute to the toxicological effects of the fungus in animals. In contrast, no biological activity could be detected for FA₁ under identical experimental conditions. These studies and others have indicated that the fumonisin B mycotoxins, although lacking mutagenicity in the Salmonella test or genotoxicity in the DNA repair assays in primary hepatocytes, appear to induce resistant hepatocytes similar to many known hepatocarcinogens.     

Susceptibility of staphylococcal biofilms to enzymatic treatments depends on their chemical composition

Bacterial infections are serious complications after orthopaedic implant surgery. Staphylococci, with Staphylococcus epidermidis as a leading species, are the prevalent and most important species involved in orthopaedic implant-related infections. The biofilm mode of growth of these bacteria on an implant surface protects the organisms from the host’s immune system and from antibiotic therapy. Therapeutic agents that disintegrate the biofilm matrix would release planktonic cells into the environment and therefore allow antibiotics to eliminate the bacteria. An addition of a biofilm-degrading agent to a solution used for washing–draining procedures of infected orthopaedic implants would greatly improve the efficiency of the procedure and thus help to avoid the removal of the implant. We have previously shown that the extracellular staphylococcal matrix consists of a poly-N-acetylglucosamine (PNAG), extracellular teichoic acids (TAs) and protein components. In this study, we accessed the sensitivity of pre-formed biofilms of five clinical staphylococcal strains associated with orthopaedic prosthesis infections and with known compositions of the biofilm matrix to periodate, Pectinex Ultra SP, proteinase K, trypsin, pancreatin and dispersin B, an enzyme with a PNAG-hydrolysing activity. We also tested the effect of these agents on the purified carbohydrate components of staphylococcal biofilms, PNAG and TA. We found that the enzymatic detachment of staphylococcal biofilms depends on the nature of their constituents and varies between the clinical isolates. We suggest that a treatment with dispersin B followed by a protease (proteinase K or trypsin) could be capable to eradicate biofilms of a variety of staphylococcal strains on inert surfaces.     

Behavioural traits mediating effects of two plant-ants on their specific myrmecophyte host

Summary. Symbiotic ant species vary in their effects on the same host plant, and some ant species are exploiters. These can destabilise the interaction. The behavioural repertoire of ant associates should be important in determining their effects on the host. We examined several traits of foraging behaviour of two ant species associated with the African understorey tree Leonardoxa africana africana – the protective mutualist Petalomyrmex phylax and the parasite Cataulacus mckeyi – to examine the mechanistic basis of the difference in their effects on the plant. These two ant species displayed significant differences not only in activity rhythms, P. phylax patrolling leaves day and night while C. mckeyi was strictly diurnal, but also in their predatory behaviour (P. phylax killed more herbivores) and recruitment dynamics (C. mckeyi recruited at a lower level). For all traits examined, C. mckeyi expressed behaviours reflecting an opportunistic exploitation of the nectar produced by the host plant, whereas those displayed by P. phylax contribute to conferring effective protection of the host plant. Our results suggest that prey capture may be important as a source of food for Petalomyrmex, in addition to its function in increasing plant-provided resources through protection.Received 27 August 2004; revised 11 November 2004; accepted 16 November 2004.     

Parasitism rates and sex ratios of a parasitoid wasp: effects of herbivore and plant quality

Summary We studied interactions among collards, Brassica oleracea var. acephala, the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Yponomeutidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae) by manipulating plant nitrogen (N) concentrations in field and laboratory experiments. Parasitoid abundance strongly reflected DBM abundance and was related to total leaf N. Parasitism rates were high (70.7%) and density-independent. Wasp sex ratios varied markedly (3–93% female) in response to the herbivores, the plants, or both. Higher proportions of female wasps emerged from DBM larvae on plants with high leaf N than on unfertilized plants. More female wasps also emerged from larvae parasitized as larger instars. We suggest that wasps have the potential to control DBM populations through long-term numerical responses mediated by variable sex ratios.     

Differential treatment ofAcetabularia with cytochalasin B and N-Ethylmaleimide with special reference to their effects on cytoplasmic streaming

Summary Cytoplasmic streaming in the stalk ofAcetabularia, ryukyuensis at the vegetative stage was reversibly inhibited by cytochalasin B (cB) of 50 g/ml and irreversibly by N-Ethylmaleimide (NEM) above concentrations of 0.25 mM.After the endoplasm and the chloroplasts were pushed forward one end of the stalk by gentle centrifugation at about 500 × g for 3 minutes, numerous ectoplasmic striations remainedin situ in the stalk cortex. The striations ran in parallel with the longitudinal axis of the stalk at unequal intervals. The endoplasm streamed back only along these striations.By combining centrifugation and a double chamber technique, the endoplasm and the cortex of the stalk were treated separately with CB or NEM. CB treatment of the cortex arrested streaming; when treatment was restricted to the endoplasm, streaming continued at an normal rate. NEM treatment restricted to the cortex permitted normal streaming rates. Treatment restricted to the moving endoplasm inhibited streaming.These results suggest that microfilaments and a moiety, possibly myosin, play an active role in the streaming. Microfilaments must reside in the cortex, especially in the ectoplasmic striations, while the putative myosin must reside in the moving endoplasm.