Biomedical subjects

Stephan D Flint

Publications and source records attributed to Stephan D Flint.

6 recordsLinked to original sources

PubMed2004

Field testing of biological spectral weighting functions for induction of UV-absorbing compounds in higher plants.

Action spectra are typically used as biological spectral weighting functions (BSWF) in biological research on the stratospheric ozone depletion issue. Despite their critical role in determining the amount of UV supplied in experiments, there has been only limited testing of different functions under realistic field conditions. Here, we calculate effective radiation according to five published BSWF and evaluate the appropriateness of these BSWF in representing the induction of UV-absorbing compounds. Experiments were carried out in the field using both ultraviolet-B radiation (280-320 nm) supplementation and selective filtering of solar UV radiation. For the four species tested, BSWF that extend into the ultraviolet-A radiation (320-400 nm) (UV-A) with moderate effectiveness best represented the observed results. When compared with the commonly used generalized plant response, these BSWF suggest that simulations of ozone depletion will require more radiation than in the past experiments. However, they imply lower radiation supplements than a new plant growth BSWF that has a greater emphasis on UV-A wavelengths.

Models, Biological↗

PubMed2003

How much variance is explained by ecologists? Additional perspectives.

A recent meta-analysis of meta-analyses by Møller and Jennions suggested that ecologists using statistical models are explaining between 2.5% and 5.42% of the variability in ecological studies. Although we agree that there is considerable variability in ecological systems that is not explained, we disagree with the approach and general conclusions of Møller and Jennions. As an alternate perspective, we explored the question: "How much ecological variation in relationships is not explained?" We did this by examining published studies in five different journals representative of the numerous sub-disciplines of ecology. We quantified the proportion of variance not explained in statistical models as the residual or random error compared to the total variation in the data set. Our results indicate that statistical models explain roughly half of the variation in variables of interest, vastly different from the 2.5%-5.42% reported by Møller and Jennions. This difference resulted largely from a different level of analysis: we considered the original study to be the appropriate level for quantifying variability while Møller and Jennions combined studies at different temporal and spatial scales and attempted to find universal single-factor relationships between ecological variables across study organisms or locations. Therefore, we believe that Møller and Jennions actually measured the universality of single factor effects across multiple ecological systems, not the amount of variability in ecological studies explained by ecologists. This study, combined with Møller and Jennions', illustrates importance of applying statistical models appropriately to assess ecological relationships.

Animals↗

PubMed2003

Terrestrial ecosystems, increased solar ultraviolet radiation and interactions with other climatic change factors.

Based on research to date, we can state some expectations about terrestrial ecosystem response as several elements of global climate change develop in coming decades. Higher plant species will vary considerably in their response to elevated UV-B radiation, but the most common general effects are reductions in height of plants, decreased shoot mass if ozone reduction is severe, increased quantities of some phenolics in plant tissues and, perhaps, reductions in foliage area. In some cases, the common growth responses may be lessened by increasing CO2 concentrations. However, changes in chemistry of plant tissues will generally not be reversed by elevated CO2. Among other things, changes in plant tissue chemistry induced by enhanced UV-B may reduce consumption of plant tissues by insects and other herbivores, although occasionally consumption may be increased. Pathogen attack on plants may be increased or decreased as a consequence of elevated UV-B, in combination with other climatic changes. This may be affected both by alterations in plant chemistry and direct damage to some pathogens. Water limitation may decrease the sensitivity of some agricultural plants to UV-B, but for vegetation in other habitats, this may not apply. With global warming, the repair of some types of UV damage may be improved, but several other interactions between warming and enhanced UV-B may occur. For example, even though warming may lead to fewer killing frosts, with enhanced UV-B and elevated CO2 levels, some plant species may have increased sensitivity to frost damage.

Climate↗

PubMedDate not supplied

Variations in UV-B tolerance and germination speed of Metarhizium anisopliae conidia produced on insects and artificial substrates.

Solar ultraviolet radiation (UV-A and UV-B) is a major factor in failure of programs using the insect pathogenic fungus Metarhizium anisopliae as a biological control agent. Studies were conducted to determine if growth conditions, viz. artificial (agar media or rice grain) or natural (infected insects) substrates for conidial production affect two traits that directly influence performance of conidia after field application: tolerance to UV-B radiation and conidial germination speed. Conidia of two isolates (ARSEF 23 and ARSEF 2575) of M. anisopliae var. anisopliae produced on potato dextrose agar plus yeast extract (PDAY) or on fungus-killed larvae of two insect species, Galleria mellonella and Zophobas morio, were inactivated by exposure to UV-B radiation. Conidia of both isolates when produced on insect cadavers were significantly more sensitive to UV-B radiation than conidia produced on PDAY. Also, conidia from insect cadavers germinated slower than those from PDAY cultures. A comparison of conidia from artificial substrates showed that conidia produced on Czapek's and Emerson's YpSs agar media or rice grains had higher tolerance to UV-B radiation and germinated faster than conidia raised on PDA and PDAY. Accordingly, the growth substrate and nutritional environment in which conidia are produced influences M. anisopliae conidial UV-B tolerance and speed of germination; and manipulation of these variables could be used to obtain conidia with increased tolerance to UV-B radiation and shorter germination times.

Animals↗

PubMedDate not supplied

Plant responses to current solar ultraviolet-B radiation and to supplemented solar ultraviolet-B radiation simulating ozone depletion: an experimental comparison.

Field experiments assessing UV-B effects on plants have been conducted using two contrasting techniques: supplementation of solar UV-B with radiation from fluorescent UV lamps and the exclusion of solar UV-B with filters. We compared these two approaches by growing lettuce and oat simultaneously under three conditions: UV-B exclusion, near-ambient UV-B (control) and UV-B supplementation (simulating a 30% ozone depletion). This permitted computation of "solar UV-B" and "supplemental UV-B" effects. Microclimate and photosynthetically active radiation were the same under the two treatments and the control. Excluding UV-B changed total UV-B radiation more than did supplementing UV-B, but the UV-B supplementation contained more "biologically effective" shortwave radiation. For oat, solar UV-B had a greater effect than supplemental UV-B on main shoot leaf area and main shoot mass, but supplemental UV-B had a greater effect on leaf and tiller number and UV-B-absorbing compounds. For lettuce, growth and stomatal density generally responded similarly to both solar UV-B and supplemented UV-B radiation, but UV-absorbing compounds responded more to supplemental UV-B, as in oat. Because of the marked spectral differences between the techniques, experiments using UV-B exclusion are most suited to assessing effects of present-day UV-B radiation, whereas UV-B supplementation experiments are most appropriate for addressing the ozone depletion issue.

Atmosphere↗

PubMedDate not supplied

Conidial pigmentation is important to tolerance against solar-simulated radiation in the entomopathogenic fungus Metarhizium anisopliae.

The importance of conidial pigmentation to solar UV radiation tolerance in the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, was estimated by comparing the effects of exposure to simulated solar UV radiation on the wild-type parent strain U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) Collection of Entomopathogenic Fungal Cultures (ARSEF) 23, which has dark green conidia, and three groups of color mutants with yellow, purple and white conidia. The comparisons included inactivation levels and the kinetics of germination of conidia exposed or not exposed to simulated solar UV radiation. In addition to significantly inactivating the conidia of different mutants, exposure to radiation delayed for several hours the germination of surviving conidia of the wild type and all mutants. In general, mutants with white conidia were more sensitive to simulated solar UV radiation than mutants with purple conidia, which were more sensitive than mutants with yellow conidia, which in turn were more sensitive than the green wild strain. A significant variation in tolerance to simulated solar radiation was observed among mutants within each color group, particularly among mutants with yellow conidia. Revertants with green conidia, DWR 179 and DWR 176, were obtained from the very sensitive UV mutants DWR 148 (yellow conidia) and DWR 149 (purple conidia), respectively. These revertants had levels of tolerance to simulated solar UV radiation similar to those of the wild-type ARSEF 23. This observation is strong evidence of the importance of green conidial pigmentation for tolerance to simulated solar UV radiation, a factor that could be manipulated to produce M. anisopliae strains with more tolerance to solar UV radiation.

Dose-Response Relationship, Radiation↗