中国香菇交配型和基因型的分析

自1987—1990,在长江以南九省(区)采集52个香菇品系,43株制作了孢子印用以检测交配型,又以检测A.B因子位点的等位基因方法测定了担孢子的基因型,保藏了以A_xB_x(或A_xB_y……)标记的标准单核菌丝体,这是建立中国香菇种质库的第一步,将为香菇杂交育种提供有效亲本。结果表明:每一菌株的四个交配型呈随机分配。具有四个交配型的菌株百分率是79%,有二个交配型的香菇菌株百分率是21%。有9个菌株的单核菌丝的基因型从A_1B_1……A_(18)B_(18)不同,A.B因子等位基因差异明显,这些菌株显示了A.B因子的很低的地区性重复频率。本项研究中建立了区分同宗A同宗B以及四个交配型的试验方法,遵循着核移动的规律,这个方法能够重复。     

The inhibitory effects of the molluscicide metaldehyde on feeding, locomotion and faecal elimination of three pest species of terrestrial slug

Single meals on maize flour pellets containing 0, 0·5, 1, 2, 4, 6, and 8% metaldehyde were analysed in Arion hortensis (agg), Deroceras reticulatum and Deroceras caruanae, by attaching the pellets to a mechanical transducer from which signals were ultimately fed into a BBC microcomputer for on-line analysis. Post-feeding tests were used to investigate toxic effects of metaldehyde and the recovery of slugs was examined daily for 7 days. Bite rates were slightly lower and more irregular on metaldehyde meals especially in A. hortensis. The meal length and number of bites per meal were markedly inhibited by metaldehyde and inversely proportional to the concentration. The size of the bites was also reduced, by about 30%, in meals on 6% pellets compared with 0%. Clear symptoms of poisoning became evident during the meal or normally in the 16-min test period immediately afterwards. In these tests slugs which fed on metaldehyde pellets showed a disruption of their ability to right themselves (after being placed on their side), less activity and a reduced probability of accepting a ‘dummy’ pellet containing no metaldehyde. It is hypothesised that feeding is prematurely terminated primarily because of the toxic effects of the metaldehyde and that aversion also acts to terminate the meal early, by decreasing the probability of continuing to feed as the meal proceeds. At higher concentrations of metaldehyde aversion may be more important than the toxic effects in ending the meal. Faecal elimination is delayed after metaldehyde meals and this contributes to mortality. The estimated lethal doses were about 0·2 mg/g body weight of slug in Deroceras spp. A. hortensis was less susceptible. To increase the likelihood of a lethal dose being ingested the inhibition of feeding needs to be overcome, at least partly, and the results presented indicate the need for a bait formulation which reduces the rate of absorption of the molluscicide from the gut.     

Does soil nitrogen influence growth,water transport and survival of snow gum (Eucalyptus pauciflora Sieber ex Sprengel.) under CO2 enrichment?

Eucalyptus pauciflora Sieber ex Sprengel. (snow gum) was grown under ambient (370  µ L L⁻¹) and elevated (700  µ L L⁻¹) atmospheric [CO₂] in open-top chambers (OTCs) in the field and temperature-controlled glasshouses. Nitrogen applications to the soil ranged from 0.1 to 2.75 g N per plant. Trees in the field at high N levels grew rapidly during summer, particularly in CO₂-enriched atmosphere, but suffered high mortality during summer heatwaves. Generally, wider and more numerous secondary xylem vessels at the root–shoot junction in CO₂-enriched trees conferred fourfold higher below-ground hydraulic conductance. Enhanced hydraulic capacity was typical of plants at elevated [CO₂] (in which root and shoot growth was accelerated), but did not result from high N supply. However, because high rates of N application consistently made trees prone to dehydration during heatwaves, glasshouse studies were required to identify the effect of N nutrition on root development and hydraulics. While the effects of elevated [CO₂] were again predominantly on hydraulic conductivity, N nutrition acted specifically by constraining deep root penetration into soil. Specifically, 15–40% shallower root systems supported marginally larger shoot canopies. Independent changes to hydraulics and root penetration have implications for survival of fertilized trees under elevated atmospheric [CO₂], particularly during water stress.     

Plasmodium berghei NK65 in the Inbred A/J Mouse: Variations in Virulence of P. berghei Demes*

SYNOPSIS. Plasmodium berghei NK65 was passed thru Anopheles stephensi to golden hamsters and mice. The percent cumulative mortality was compared after each mosquito passage in early (7–13) blood passages. The strain was found to have divided into demes (populations) retaining original virulence and demes which were less virulent. The separation of virulent and less virulent demes was traced to its origin. Both virulent and less virulent demes can be passed thru mosquitoes and hamsters. No concomitant organism has been identified.     

Demonstration and Preliminary Characterization of an Enzyme Capable of the Further Metabolism of the Thymidine Catabolite, β-Aminoisobutyric Acid,in Tetrahymena pyriformis Strain GL1

ABSTRACT. The enzyme that catalyzes the critical conversion of the proposed reductive thymidine catabolic end product, P-aminoisobutyric acid, to the initial anabolic reutilization substrate, probably methylmalonic semialdehyde, was investigated to un- ambiguously substantiate the operation of a reductive pyrimidine catabolic and reutilization pathway in Tetrahymena pyriformis strain GL. Although most of the studies on the further metabolism of P-aminoisobutyric acid in other organisms suggested transamination of p-aminoisobutyric acid to methylmalonic semialdehyde followed by its further oxidation to methylmalonic acid, such a transaminating system could not be demonstrated. By means of a sensitive fluorometric assay system, however, a low, but significant amount of P-aminoisobutyric acid oxidase activity was detected. This enzymatic activity exhibited the following characteristics in homogenates: good activity in alkaline 0.2 M Tris-HCI buffer with a rather broad pH optimum ranging from 7.8 to 9.0; optimum activity at a temperature of 37°C; stimulation on the addition of exogenous FAD; inhibition on the addition of divalent cations, EDTA, or PCMB; little stimulation on the addition of detergents; and no increase in activity on repeated freezing and thawing. In addition, crude preparations of this oxidase were found to be relatively stable when stored up to one week either refrigerated or frozen, to have a specific activity of 2.8 nmoles/min/mg of protein, and to have a K, of 3.6 × 10^? M for d,l -β-aminoisobutyric acid. Whether this high K_m, is physiologically significant or not, however, will have to await further investigation. Preliminary (NH₄)₂SO₄ fractionation and affinity chromatography studies also indicated that this enzyme appears to be a unique and specific oxidase whose activity is separable from other marker enzymes, including other oxidases.     

Seasonal effects and fine‐scale population dynamics of Aedes taeniorhynchus,a major disease vector in the Galapagos Islands

Characterization of the fine‐scale population dynamics of the mosquito Aedes taeniorhynchus is needed to improve our understanding of its role as a disease vector in the Galapagos Islands. We used microsatellite data to assess the genetic structure of coastal and highland mosquito populations and patterns of gene flow between the two habitats through time on Santa Cruz Island. In addition, we assessed possible associations of mosquito abundance and genetic diversity with environmental variables. The coastal and highland mosquito populations were highly differentiated from each other all year round, with some gene flow detected only during periods of increased precipitation. The results support the hypothesis that selection arising from ecological differences between habitats is driving adaptation and divergence in A. taeniorhynchus, and maintaining long‐term genetic differentiation of the populations against gene flow. The highland and lowland populations may constitute an example of incipient speciation in progress. Highland populations were characterized by lower observed heterozygosity and allelic richness, suggesting a founder effect and/or lower breeding site availability in the highlands. A lack of reduction in genetic diversity over time in highland populations suggests that they survive dry periods as dormant eggs. Association between mosquito abundance and precipitation was strong in the highlands, whereas tide height was the main factor affecting mosquito abundance on the coast. Our findings suggests differences in the infection dynamics of mosquito‐borne parasites in the highlands compared to the coast, and a higher risk of mosquito‐driven disease spread across these habitats during periods of increased precipitation.     

Freeze avoidance: a dehydrating moss gathers no ice

Using cryo‐SEM with EDX fundamental structural and mechanical properties of the moss Ceratodon purpureus (Hedw.) Brid. were studied in relation to tolerance of freezing temperatures. In contrast to more complex plants, no ice accumulated within the moss during the freezing event. External ice induced desiccation with the response being a function of cell type; water‐filled hydroid cells cavitated and were embolized at ?4 °C while parenchyma cells of the inner cortex exhibited cytorrhysis, decreasing to ～20% of their original volume at a nadir temperature of ?20 °C. Chlorophyll fluorescence showed that these winter acclimated mosses displayed no evidence of damage after thawing from ?20 °C while GCMS showed that sugar concentrations were not sufficient to confer this level of freezing tolerance. In addition, differential scanning calorimetry showed internal ice nucleation occurred in hydrated moss at ～?12 °C while desiccated moss showed no evidence of freezing with lowering of nadir temperature to ?20 °C. Therefore the rapid dehydration of the moss provides an elegantly simple solution to the problem of freezing; remove that which freezes.