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• 1. [Article] Cytophotometric determinations of nuclear DNA content in tissues of the wax moth larva, Galleria mellonella Linnaeus

  The present study was undertaken to determine, by measurement of nuclear DNA, the degrees and frequencies of ploidy in the last larval instar of the moth Galleria mellonella Linnaeus. While such data have ...

  Citation × Citation Citation Abstract Copy Title: Cytophotometric determinations of nuclear DNA content in tissues of the wax moth larva, Galleria mellonella Linnaeus Author: Longo, Frank J., 1939- The present study was undertaken to determine, by measurement of nuclear DNA, the degrees and frequencies of ploidy in the last larval instar of the moth Galleria mellonella Linnaeus. While such data have been amassed for a wide variety of vertebrate tissues, few studies have been concerned with invertebrates and especially insects where somatic polyploidy is developed to an unusually high degree. Relative amounts of DNA were determined cytophotometrically on individual Feulgen-stained nuclei of hypodermis, ventriculus, fat cells, blood cells, anterior silk gland, and proventriculus. Graphs of the determined DNA values indicated the presence of nuclear classes falling into polyploid ratios, The majority of blood cell and fat cell nuclei had class I values (= diploid), while class II and III (= tetraploid and octoploid) DNA values represented about 17 to 20 percent of the total nuclear population. The majority of DNA values of the ventriculus nuclei fell into the second class while 6.8 percent were considered as class I. The hypodermal nuclei were mostly of class I, while class II values represented 5.5 percent of the total number of determinations. Nuclei of the proventriculus and the anterior silk gland showed a broad spectrum of DNA values ranging from classes IV to VIII including many intermediate values. The method of measurement was analyzed for sources of error. Various interpretations were offered for the variations in DNA values including the role of endomitosis, definitive polyploidy, aneuploidy, differential gene replication, etc. In the case of the anterior silk gland and the proventriculus a possible relationship between DNA amounts and ceIl activity is indicated. Title: Cytophotometric determinations of nuclear DNA content in tissues of the wax moth larva, Galleria mellonella Linnaeus Author: Longo, Frank J., 1939- The present study was undertaken to determine, by measurement of nuclear DNA, the degrees and frequencies of ploidy in the last larval instar of the moth Galleria mellonella Linnaeus. While such data have been amassed for a wide variety of vertebrate tissues, few studies have been concerned with invertebrates and especially insects where somatic polyploidy is developed to an unusually high degree. Relative amounts of DNA were determined cytophotometrically on individual Feulgen-stained nuclei of hypodermis, ventriculus, fat cells, blood cells, anterior silk gland, and proventriculus. Graphs of the determined DNA values indicated the presence of nuclear classes falling into polyploid ratios, The majority of blood cell and fat cell nuclei had class I values (= diploid), while class II and III (= tetraploid and octoploid) DNA values represented about 17 to 20 percent of the total nuclear population. The majority of DNA values of the ventriculus nuclei fell into the second class while 6.8 percent were considered as class I. The hypodermal nuclei were mostly of class I, while class II values represented 5.5 percent of the total number of determinations. Nuclei of the proventriculus and the anterior silk gland showed a broad spectrum of DNA values ranging from classes IV to VIII including many intermediate values. The method of measurement was analyzed for sources of error. Various interpretations were offered for the variations in DNA values including the role of endomitosis, definitive polyploidy, aneuploidy, differential gene replication, etc. In the case of the anterior silk gland and the proventriculus a possible relationship between DNA amounts and ceIl activity is indicated. Close

• 2. [Article] Developing a Real-Time PCR Assay for Detection and Quantification of Pratylenchus neglectus in Soil

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by The American ...

  Citation × Citation Citation Abstract Copy Title: Developing a Real-Time PCR Assay for Detection and Quantification of Pratylenchus neglectus in Soil Author: Smiley, Richard W., Okubara, Patricia A., Reardon, Catherine L., Yan, Guiping, Skantar, Andrea M. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by The American Phytopathological Society and can be found at: https://www.apsnet.org/publications/Pages/default.aspx. Title: Developing a Real-Time PCR Assay for Detection and Quantification of Pratylenchus neglectus in Soil Author: Smiley, Richard W., Okubara, Patricia A., Reardon, Catherine L., Yan, Guiping, Skantar, Andrea M. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by The American Phytopathological Society and can be found at: https://www.apsnet.org/publications/Pages/default.aspx. Close

• 3. [Article] Activity, composition and structure of soil microbial communities in Savannah shrubs of agroecosystems in semi-arid Senegal

  Piliostigma reticulatum and Guiera senegalensis are two native shrubs that coexist with row crops in parkland systems of the Sahel of Africa. Although permanently green all year around in soil depleted ...

  Citation × Citation Citation Abstract Copy Title: Activity, composition and structure of soil microbial communities in Savannah shrubs of agroecosystems in semi-arid Senegal Author: Diedhiou, Sire Piliostigma reticulatum and Guiera senegalensis are two native shrubs that coexist with row crops in parkland systems of the Sahel of Africa. Although permanently green all year around in soil depleted in nutrients and dry for a nine-month period, these shrubs have been largely overlooked. Conventional management of these shrubs involves coppicing and burning of aboveground biomass each spring to prepare for the summer cropping season. Previous research has shown these shubs can provide high amount of biomass carbon at landscape levels and that they can, through their roots, move water from the wet subsoil to the dry surface soil at night when photosynthesis stops (hydraulic redistribution). However, the influence of these shrubs on the soil microbial communities and their role in biogeochemical processes is largely unknown. This dissertation reports studies that have been carried out to investigate the impact of these shrubs on the soil microbial communities. The rhizosphere effect of these two dominant shrubs was investigated during both the rainy season and dry season by studying the soil microbial structure, composition and activity. This was done by: 1) profiling microbial communities through phospholipids fatty acid (PLFA) analysis and denaturing gradient gel electrophoresis (DGGE); 2) assaying enzymes (acid phosphatase, β-glucosidase, cellulase, chitinase, urease); and 3) measuring microbial biomass carbon (MBC) and mineral nitrogen dynamics. Decomposition studies were conducted to determine the potential of nonthermal management of shrub residues. This was done by determining the influence of shrub canopy, macrofauna, and residue type on shrub litter decomposition and microbial dynamics under field and laboratory conditions. Microbial communities were more diverse, more active and had greater biomass in shrub rhizospheres. The rhizosphere communities during the dry season were similar to the rhizosphere and bulk communities during the wet season. This suggests that shrub rhizosphere provide root exudates and/or water via hydraulic redistribution that supports microbial communities during the dry season. PLFA and enzyme activities were highly correlated and were more sensitive than DGGE in distinguishing the communities temporally and spatially. PLFA profiling showed that the rhizosphere effect was dominated by fungi and Gram-positive bacteria communities, and stimulated acid phosphatase and β-glucosidase activities. Macrofauna access to shrub residue resulted in higher decomposition rates with 70 to 90% loss of mass after 210 days. There was an increase of MBC and enzyme activities when macrofauna were allowed, and beneath shrub canopy as opposed to outside of the canopy. In a laboratory incubation study, the influence of shrub rhizosphere/canopy on soil was greater than the residue effect on the activity of soil microbial communities. Decomposition of residues showed that leaf litter had a greater impact on soil microbial communities and enzyme activities than did stem materials or stem/leaf mixes. Cellulase and β-glucosidase were highly correlated with the fungal markers and Gram-positive bacteria markers. In conclusion, the results showed that Piliostigma reticulatum and Guiera senegalensis are stimulating microbial activity and communities even in the dry season after six or more months without rainfall. Besides C inputs through litter fall, root turnover and exudates, this suggests that shrubs maintain moisture levels in the dry season for microorganisms by performing hydraulic redistribution of water from wet subsoils to dry surface soils at night through a passive water potential gradient. Consequently, shrubs are maintaining soil health and can drive biogeochemical processes year round which has not been previously recognized. These results provide a foundation to actively manage these shrubs to conserve Sahelian landscapes and to optimize agricultural productivity. Title: Activity, composition and structure of soil microbial communities in Savannah shrubs of agroecosystems in semi-arid Senegal Author: Diedhiou, Sire Piliostigma reticulatum and Guiera senegalensis are two native shrubs that coexist with row crops in parkland systems of the Sahel of Africa. Although permanently green all year around in soil depleted in nutrients and dry for a nine-month period, these shrubs have been largely overlooked. Conventional management of these shrubs involves coppicing and burning of aboveground biomass each spring to prepare for the summer cropping season. Previous research has shown these shubs can provide high amount of biomass carbon at landscape levels and that they can, through their roots, move water from the wet subsoil to the dry surface soil at night when photosynthesis stops (hydraulic redistribution). However, the influence of these shrubs on the soil microbial communities and their role in biogeochemical processes is largely unknown. This dissertation reports studies that have been carried out to investigate the impact of these shrubs on the soil microbial communities. The rhizosphere effect of these two dominant shrubs was investigated during both the rainy season and dry season by studying the soil microbial structure, composition and activity. This was done by: 1) profiling microbial communities through phospholipids fatty acid (PLFA) analysis and denaturing gradient gel electrophoresis (DGGE); 2) assaying enzymes (acid phosphatase, β-glucosidase, cellulase, chitinase, urease); and 3) measuring microbial biomass carbon (MBC) and mineral nitrogen dynamics. Decomposition studies were conducted to determine the potential of nonthermal management of shrub residues. This was done by determining the influence of shrub canopy, macrofauna, and residue type on shrub litter decomposition and microbial dynamics under field and laboratory conditions. Microbial communities were more diverse, more active and had greater biomass in shrub rhizospheres. The rhizosphere communities during the dry season were similar to the rhizosphere and bulk communities during the wet season. This suggests that shrub rhizosphere provide root exudates and/or water via hydraulic redistribution that supports microbial communities during the dry season. PLFA and enzyme activities were highly correlated and were more sensitive than DGGE in distinguishing the communities temporally and spatially. PLFA profiling showed that the rhizosphere effect was dominated by fungi and Gram-positive bacteria communities, and stimulated acid phosphatase and β-glucosidase activities. Macrofauna access to shrub residue resulted in higher decomposition rates with 70 to 90% loss of mass after 210 days. There was an increase of MBC and enzyme activities when macrofauna were allowed, and beneath shrub canopy as opposed to outside of the canopy. In a laboratory incubation study, the influence of shrub rhizosphere/canopy on soil was greater than the residue effect on the activity of soil microbial communities. Decomposition of residues showed that leaf litter had a greater impact on soil microbial communities and enzyme activities than did stem materials or stem/leaf mixes. Cellulase and β-glucosidase were highly correlated with the fungal markers and Gram-positive bacteria markers. In conclusion, the results showed that Piliostigma reticulatum and Guiera senegalensis are stimulating microbial activity and communities even in the dry season after six or more months without rainfall. Besides C inputs through litter fall, root turnover and exudates, this suggests that shrubs maintain moisture levels in the dry season for microorganisms by performing hydraulic redistribution of water from wet subsoils to dry surface soils at night through a passive water potential gradient. Consequently, shrubs are maintaining soil health and can drive biogeochemical processes year round which has not been previously recognized. These results provide a foundation to actively manage these shrubs to conserve Sahelian landscapes and to optimize agricultural productivity. Close

• 4. [Article] The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle

  The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle were investigated by studying the time-resolved fluorescence anisotropy decays of ethidium bromide intercalated ...

  Citation × Citation Citation Abstract Copy Title: The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle Author: Winzeler, Elizabeth A. The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle were investigated by studying the time-resolved fluorescence anisotropy decays of ethidium bromide intercalated into the DNA of the core particle. As the torsional flexibility of DNA is affected by the presence of an intercalating dye, the decays were studied at different ethidium bromide to core particle binding ratios. The anisotropy decays were collected using the method of time-resolved single-photon counting and were fit to a model developed by J. M. Schurr (Schurr, 1984) using a non-linear least squares fitting algorithm developed by the author for this purpose. It was shown that below a binding ratio of 0.1 there was no demonstrable change in the anisotropy as a function of binding ratio. Our results show, that the apparent torsional flexibility of DNA of to a nucleosome core particle is dependent on the number of base pairs of the DNA between points of attachment to the histone core. If this number is as high as 30 base pairs, then the torsional flexibility of DNA on a nucleosome core particle is as high or higher than DNA free in solution. Also, for reasonable values of N, the friction felt by the DNA on a core particle is much higher than that felt by free DNA. This indicates that the DNA on a core particle is highly constrained in its motions. The hydrogen ion concentration was shown to have a substantial effect on the fluorescent anisotropy decays, particularly in the early regions of the decay. These analyses indicated that the observed change could be attributed to either a loosening of the contacts between the DNA and the histone core, or a relaxing of the torsional flexibility of the DNA. Title: The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle Author: Winzeler, Elizabeth A. The effects of pH on the torsional flexibility of DNA bound to a nucleosome core particle were investigated by studying the time-resolved fluorescence anisotropy decays of ethidium bromide intercalated into the DNA of the core particle. As the torsional flexibility of DNA is affected by the presence of an intercalating dye, the decays were studied at different ethidium bromide to core particle binding ratios. The anisotropy decays were collected using the method of time-resolved single-photon counting and were fit to a model developed by J. M. Schurr (Schurr, 1984) using a non-linear least squares fitting algorithm developed by the author for this purpose. It was shown that below a binding ratio of 0.1 there was no demonstrable change in the anisotropy as a function of binding ratio. Our results show, that the apparent torsional flexibility of DNA of to a nucleosome core particle is dependent on the number of base pairs of the DNA between points of attachment to the histone core. If this number is as high as 30 base pairs, then the torsional flexibility of DNA on a nucleosome core particle is as high or higher than DNA free in solution. Also, for reasonable values of N, the friction felt by the DNA on a core particle is much higher than that felt by free DNA. This indicates that the DNA on a core particle is highly constrained in its motions. The hydrogen ion concentration was shown to have a substantial effect on the fluorescent anisotropy decays, particularly in the early regions of the decay. These analyses indicated that the observed change could be attributed to either a loosening of the contacts between the DNA and the histone core, or a relaxing of the torsional flexibility of the DNA. Close