Showing papers by "Wageningen University and Research Centre published in 1990"

Characterization of soil organisms involved in the degeneration of ammophila-arenaria

Abstract: The degeneration of Ammophila arenaria (marram grass) in stable stages of coastal foredunes may be due to pathogenic or parasitic soil organisms. To test this, and to characterize the organisms involved, biocides were applied to sand collected from the root zone of natural stands of A. arenaria. Seedlings of A. arenaria were grown and biomass production was measured and compared with growth of seedlings in γ-irradiated soil to determine effects of applied biocides. Sand from stable and mobile foredune sections (degenerated and vigorous A. arenaria, respectively) was examined. Improved seedling growth followed fungicide and ncmaticide treatments m sand from stable, as well as from mobile foredunes. On the other hand, bactericides (streptomycin and penicillin) had no effect. The fungicide propamocarb only stimulated growth very weakly, whereas the fungicide benomyl increased growth significantly. However, the effect of benomyl may not be solely due to its fungiddal action, as it also prevented root infection by the nematodes Heterodera (avenae group) and Meloidogyne maritima. The highest increase in yield was obtained with the nematicide oxamyl, which prevented root-infection by endo-parasitic nematodes (Heterodera avenae group, M. maritima and Pratylenchus sp.). Oxamyl also reduced numbers of ecto-parasitic nematodes. It is concluded that plant parasitic nematodes could be important in the degeneration of A. arenaria, but that interactions with other groups of soil organisms, such as soil fungi, cannot be excluded.

Glucose tolerance and hyperinsulinaemia in obese women: role of adipose tissue distribution, muscle fibre characteristics and androgens.

Abstract: The separate independent statistical contribution of abdominal distribution of fat, hyperandrogenicity and muscle morphology to glucose intolerance and hyperinsulinaemia was analysed in 88 obese women. In univariate analyses the waist/hip circumference ratio (WHR), body fat and lean body mass were all positively associated, and SHBG levels were negatively associated with insulin and glucose values. Muscle fibre areas were positively correlated with insulin but not with glucose concentrations. Adjustment for other variables did not remove the positive association between WHR and fasting insulin and glucose concentrations. SHBG, free testosterone and type IIb fibre areas were, however, significant confounding factors in the relationship between WHR and summed insulin and glucose concentrations. We conclude that fat distribution in obese women is associated with fasting hyperglycaemia and hyperinsulinaemia, independently of androgens and muscle fibre morphology, but that reduced SHBG concentrations and increased type IIb fibre areas may partly explain increased glucose and insulin responses to an oral glucose load in abdominally obese women.

Lettuce big-vein virus: mechanical transmission and relationships to tobacco stunt virus

Abstract: Summary Big-vein diseased lettuce plants contained an agent that could consistently be transmitted mechanically to Chenopodium quinoa, in which it caused characteristic local lesions. Mechanical transmission was also possible to five other plant species including Nicotiana benthamiana, N. clevelandii and N. occidentalis, but not to lettuce. Symptoms in N. occidentalis were reminiscent of those of tobacco stunt disease. With zoospores of originally virus-free Olpidium brassicae, subcultured on the roots of N. occidentalis-P1, sap-inoculated either from lettuce or via C. quinoa, the agent could be transferred back to lettuce in which characteristic symptoms of big-vein were reproduced. Infectivity in sap at room temperature was reduced by half after 2 h, and was practically lost after one day. Thermal inactivation was considerable at 45°C and complete at 50°C. Most infectivity was lost at dilution 1:5, and the dilution end-point was 1:10. The agent survived well in leaf material stored at -80°C, or in sap from leaves ground in buffer with DIECA and activated charcoal and freeze-dried. Mechanical transmission required low dilution (1:2) in the buffer with charcoal, and chilling of materials and utensils. In lettuce, N. occidentalis-P1 and C. quinoa, with all isolates tested but one, infection was always associated with the presence of rod-shaped particles which in the literature have been associated with lettuce big-vein, and are similar to those described for tobacco stunt. Results obtained corroborate the assumption that these particles are the virions of lettuce big-vein virus. The virus also resembles tobacco stunt virus in mechanical transmissibility, instability in sap and symptoms on N. occidentalis.

Synergistic effect of 1-aminocyclopropane-1-carboxylic acid and ethylene during senescence of isolated carnation petals

Abstract: The effects of ethylene (C2H4), (2-chloroethyl)phosphonic acid (ethefon) and 1-aminocyclopropane-1-carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers (Dianthus caryophyllus L. cv. White Sim) were investigated. Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated. The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC. In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.

Adults, Adolescents, And Architects: Differences in Perception of the Urban Environment

Abstract: The main objective of this article is to contribute to theory development and methodology with respect to perceptual schemes and their influence on judgment and evaluation of the urban environment....

Effects of sulphur dioxide on leaf photosynthesis: the role of temperature and humidity

Abstract: The effect of temperature and humidity on SO2–induced photosynthetic depression was determined in gas exchange experiments with leaves of Vicia faba, L. Stomatal behaviour was sensitive to humidity resulting in higher uptake rates of SO2 and stronger reductions of photosynthesis at low VPD (vapour pressure deficit). After a fumigation period of 2 h, when the photosynthetic rate had stabilized, photosynthesis of leaves exposed to SO2 at 8°C was reduced much more than at 18°C at the same rate of SO2 uptake. Data analysis with a mechanistic model revealed that this effect was due to the slower rate of S(IV) oxidation at lower temperatures, resulting in higher accumulation of S(IV) and thus stronger reduction of photosynthesis. These results were confirmed by experimental analyses of the S(IV) concentration in leaves following fumigation, which showed that more S(IV) accumulated in leaves exposed at a lower temperature. This may explain the high sensitivity of plants exposed to SO2 under winter conditions, when both VPD and temperature are low.

Cryoscanning electron microscopy of a layer of extracellular polysaccharides produced by bacterial colonies

Abstract: Cryo-SEM allowed observation of a layer of extracellular polysaccharides that covered colonies of the bacterium Pseudomonas aeruginosa, growing on agar substrate. The layer was not found when using conventional preparation techniques and scanning electron microscopy. It disappeared partially as a result of glutaraldehyde fixation, but mainly during alcohol dehydration and critical point drying.

Photopyroelectric Detection of Phase Transitions in Thermally Thick Solids

Abstract: Enhanced photopyroelectric signal anomalies are found in the critical region for thermally thick solids. This effect is proposed as a sensitive method for the detection of phase transitions.