Relationships among strains of bean common mosaic virus and blackeye cowpea mosaic virus - members of the potyvirus group

In host-range studies, bean common mosaic virus strains (BCMV-NL1, -NL3 and -NY 15) usually induced distinct systemic symptoms in susceptible bean cultivars and latent infection in several Vigna genotypes (except NY15 which gave mosaic symptoms in the latter), while blackeye cowpea mosaic virus (B1CMV-W) caused distinct systemic symptoms in several Vigna genotypes and only weak systemic symptoms in a few bean genotypes only. Biologically, B1CMV-W was closest to BCMV-NY15 and less close to -NL1. When using antisera to the three BCMV strains and five strains of B1CMV (including a strain originally considered cowpea aphid-borne mosaic virus CAMV-Mor) in SDS-immunodiffusion and ELISA, BCMV-NL1 and -NY15 were found to be closely related to each other and to BICMV-Fla, -NR and -W, and less closely to BICMV-Ind and -Mor. Serological relationships of BCMV-NL1 and -NY15 to BCMV- NL3 were more distant, which is in line with the biological distinction of NL3 in causing temperature-independent necrosis in bean cultivars with the necrosis gene I. PAGE analysis of coat proteins revealed that the three strains of BCMV and B1 CMV-W have similar but non-identical molecular masses. Although molecular hybridisation may further elucidate quantitative relationships between potyvir-uses, variation within and among the potyviruses may continue to pose problems in their classification and identification.     

Body size, prey handling efficiency and choice of diet in three coniferous forest tits (Paridae)

The main purpose of this study was to link morphological differences between great tit ( Parus major ), willow tit ( P. montanus ) and coal tit ( P. ater ) and their rate of energy acquisition and choice of diet in order to explore the potential for competitive relations between them more directly. Handling times were measured in the laboratory by presenting mealworms of different sizes to the birds. Great tits were more efficient in handling large prey than were the smaller-bodied willow- and coal tits; for small prey sizes the coal tit was the least efficient species. Using the ratio of prey mass to the handling time value, a utility function for each species was constructed. These results suggests a potential for a segregation of the species on the food axis. However, results from the prey choice experiment show that despite considerable differences in functional morphology between the three species they do not differ significantly in the range of prey size exploited. My results suggest that the alleged importance of prey size partitioning is not likely to play the major role for the coexistence of these coniferous forests tits.     

A note on the bias due to omitted confounders

In observational studies some confounders may be unknown andtherefore omitted from the analysis while others are adjustedfor. Approximations to the functions defining the relationshipbetween the parameters in the full and reduced models are proposedleading to asymptotic bias estimates. Numerical calculationsfor logistic and Poisson regression models show good agreementbetween asymptotic and simulation bias. A data set containingthe relationship between low birth weight and smoking (Hosmer& Lemeshow, 1989) is used as an illustration.     

Primary production studies in two linked but contrasting Welsh lakes

SUMMARY. Llyn Padarn and Llyn Peris have distinct phytoplankton populations. During 1975–76, the standing crop measured as chlorophyll- a was 5.5 times greater in Padarn than in Peris and the production rate, determined by the ¹⁴CO₂ method, was faster by 3.4 times. These differences were attributed to the higher concentrations of phosphorus in the lower lake caused by treated sewage effluent. Incident light intensity, which was slightly lower in Peris due to mountain shading, and temperature, which was 1–4°C higher in Padarn, made little significant contribution to these differences during the summer. The reduced transparency of Padarn water, compared with that of Peris, resulted from denser phytopiankton crops in Padarn. During the summer, Padarn exhibited carbon dioxide depletion which correlated with the chlorophyll concentration. Light inhibition at the surfaces of both lakes correlated with solar radiation intensity. However, the relationship between pigment content and maximum photosynthetic rate was poor. Extracellular products accounted for about 16% of the total production in the lakes. Uptake of ¹⁴C-labelled acetate was low compared with that of ¹⁴CO₂ uptake.     

FURTHER STUDIES ON THE REPRODUCIBILITY OF EXTINCTION TIME ESTIMATES

SUMMARY: Alterations in peptone concentration, pH and time of autoclaving of peptone water resulted in considerable variation in extinction time estimates. The longest extinction times were obtained with the higher peptone concentration, pH 7·0 and the shorter period of autoclaving.     

Growth of Trypanosoma cruzi in Cultures of Chick Embryo Cells, and Effects of Furazolidone and Tris (p-Aminophenyl)Carbonium Chloride

SYNOPSIS. Monolayers of cells of coverslips were produced by culturing known numbers of trypsinized chick cells in growth medium (solution 199 plus 20% calf serum) at 37 C for 2 days. The fluid was then replaced with maintenance medium (solution 199 plus 5% calf serum) containing various known numbers of T. cruzi and the preparations were incubated at 33 C for 5 days; fresh maintenance medium was substituted on the 2nd or 3rd day. The inocula of parasites were obtained from T. cruzi -cell cultures, supplemented with 2% sterile NNN overlay, or from NNN cultures.
The numbers of extracellular parasites, proportions of infected cells, and percentage distribution of infected cells relative to the number of intracellular leishmanial bodies were determined on days 2 or 3 and 5 of parasite cultivation in many experiments. Analyses of the data gave the following results. Extracellular parasites increased 2- to 14-fold during the first 2 or 3 days, depending upon the source and size of the inocula, and 10- to 20-fold during the last 2 or 3 days. Cell infection continued throughout incubation at daily rates of 1.4-4.5%; 8-22% of the cells became infected during the 5 days of incubation. Intracellular growth was reflected most clearly by increases in the proportion of cells having >10 leishmanial bodies. This increase was about 5% daily during the last 2 or 3 days of incubation.
A useful test procedure for assessing the antiparasitic action and chick embryo cell toxicity of drugs is illustrated by data obtained with furazolidone and tris ( p -aminophenyl)carbonium chloride.     

Bimodal Respiration in Aquatic and Terrestrial Apodan Amphibians

SYNOPSIS. New data on resting metabolism, aerobic capacity,respiratory morphology and bimodal breathing capacities offourcaecilian species were combined with previously known data oncaecilian and amphibian biology to discern differing or unifyingthemes of gas exchange within the Gymnophiona and among theAmphibia. Discoveries include 1) a uniform resting metabolismamong caecilians that is distinctly lower than that of anuransand urodeles, 2) an aerobic capacity following activity thatrivals or exceeds that of other amphibians, and 3) despite previoussuggestions to the contrary, a substantial contribution of theskin to respiratory gas exchange, apparently sufficient to sustainthe low resting metabolism. In contrast, pulmonary gas transportappears to dominate during metabolic recovery from exercise,which is comparatively fast. The contributing roles of the skinand lungs to this extreme scope of respiratory needs in caeciliansare further discussed in light of the structural nature of andcirculatory supply to each respiratory bed, and the respiratoryproperties of caecilian blood.     

The nature of protein differentiation in the growing pea root

Abstract Sections of the growing root of pea (Pisum sativum) have been microdissected into stele, cortex and epidermis. Using labelled amino acids, two dimensional separations employing non-equilibrium pH gel electrophoresis (NEPHGE) and isoelectric focusing (IEF), and silver staining, the complexity of protein differences between the cortex and the stele has been assessed. Analyses commenced as cells in these two tissues appear in the meristem (0.7—1 mm from the tip) and continued up to 30 mm from the tip as they subsequently mature. From the earliest stages at which the cortex and stele can be distinguished and dissected apart the protein patterns differ substantially. However these tissue differences, involving over one third of the detected protein species, are almost all quantitative. Very few qualitative (i.e. tissue specific) proteins were detected. Many proteins also show quantitative stage-specific variation, detected using successively older root segments. In vitro translation studies involving isolated mRNA showed only a very limited stage-specific variation in translated proteins. This supports the notion that translational controls may contribute significantly to the development of these two tissue types.     

Nitrogen Fixation by Subterranean Clover at Varying Stages of Nodule Dehydration: I. CARBOHYDRATE STATUS AND SHORT-TERM RECOVERY OF NODULATED ROOT RESPIRATION

The nodule water potential (_nod) of subterranean clover (Trifoliumsubterraneum L.) cv. Seaton Park incubated in a flow-throughgas-exchange system was induced to decline independently ofleaf water potential (₁) by passing a continuous dry airstreamover the nodulated roots of intact well-watered plants. Reducedtranspiration by plants whose nodules had become dehydratedwas hypothesized to be related to the decline in nitrogen fixation.Whole-plant and nodule soluble carbohydrates increased as _noddeclined. Throughout an 8 d period of continual nodule dehydration,the gaseous diffusion resistance of nodules increased and theoptimum pO₂ for nitrogenase activity declined from 52 to 28kPa. Following rehydration of the nodulated roots between days4 and 5 and between days 7 and 8, nodulated root respirationincreased to or above pre-stress levels whereas nitrogenaseactivity did not recover. Re-establishment of initial ratesof nodulated root respiration was due to the stimulation ofgrowth and maintenance respiration, not to the respiration coupledto nitrogenase activity. Although no recovery of nitrogenaseactivity occurred, the elapsed time from the introduction ofacetylene into the gas stream flowing past the nodules untilmeasurement of the acetylene-induced decline in nitrogenaseactivity, decreased substantially. This was characteristic ofan increase in the permeability of the nodules to gaseous diffusionupon rehydration. However, calculated values of nodule diffusionresistance after the 24 h periods of rehydration did not indicateany recovery of gaseous diffusion resistance based on measurementsof the respiration coupled to nitrogenase activity. Hence, useof a diffusion analogue (i.e. Fick's Law) in conjunction withnodule respiratory CO₂ efflux was unable to predict changesin permeability of the variable barrier of legume nodules followingnodule dehydration and recovery. Key words: Subterranean clover, gaseous diffusion, respiration, carbohydrates, drought     

Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study

Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of free‐air‐CO₂‐enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18‐year‐old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO₂ availability. Averaged over all 6 years of the study, CO₂ enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO₂ enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO₂‐enrichment on fine root proliferation tended to shift from shallow (0–15 cm) to deeper soil depths (15–30) with increasing duration of the study. Diameters of fine roots were initially increased by CO₂‐enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m^?2 yr^?1 in CO₂‐enriched plots and 130 g dw m^?2 yr^?1 in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m^?2 yr^?1 in CO₂‐enriched plots. A lack of consistent CO₂× year effects suggest that the positive effects of CO₂ enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO₂ fumigation). Although CO₂‐enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south‐eastern pine forests.