The regulation of body weight and composition involves input from genes and the environment, demonstrated, for example, by the variable susceptibility of inbred strains of mice to obesity when offered a high-fat diet. The identification of the gene responsible for obesity in the ob/ob mouse provides a new approach to defining links between diet and genetics in the regulation of body weight. The ob gene protein product, leptin, is an adipocyte-derived circulating protein. Administration of recombinant leptin reduces food intake and increases energy expenditure in ob/ob mice, suggesting that it signals to the brain the magnitude of fat stores. Information on the regulation of this protein is limited. In several rodent models of obesity including db/db, fa/fa, yellow (Ay/a) VMH-lesioned, and those induced by gold thioglucose, monosodium glutamate, and transgenic ablation of brown adipose tissue, leptin mRNA expression and the level of circulating leptin are increased, suggesting resistance to one or more of its actions. We have assessed the impact of increased dietary fat on circulating leptin levels in normal FVB mice and FVB mice with transgene-induced ablation of brown adipose tissue. We find that high-fat diet evokes a sustained increase in circulating leptin in both normal and transgenic mice, with leptin levels accurately reflecting the amount of body lipid across a broad range of body fat. However, despite increased leptin levels, animals fed a high-fat diet became obese without decreasing their caloric intake, suggesting that a high content of dietary fat changes the 'set point' for body weight, at least in part by limiting the action of leptin.

tem is more effective if tillage and planting are performed along the contour. Schwab et al. (1993) estimated soil Agroforestry production systems have been introduced in temperloss with the universal soil loss equation to be as low as ate regions to improve water quality and diversify farm income. Agro-5.1 Mg ha Ϫ1 yr Ϫ1 for strip cropping, which was comparaforestry and grass-legume buffer effects on soil hydraulic properties ble with soil loss with terraces. Grass buffer strips reduce for a Putnam soil (fine, smectitic, mesic Vertic Albaqualf) were evaluated in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] water-runoff and increase infiltration upslope from the strips; shed in northeastern Missouri. The no-till management watershed Schmitt et al. (1999) observed that doubling the width was established in 1991 with agroforestry buffers implemented in 1997. of a 7.5-m-wide grass strip doubled water infiltration into Agroforestry buffers, 4.5 m wide and 36.5 m apart, consist of redtop the soil. A multispecies riparian buffer increased the infil-(Agrostis gigantea Roth), brome (Bromus spp.), and birdsfoot trefoil tration rate five times compared with cultivated and (Lotus corniculatus L.) with pin oak (Quercus palustris Muenchh.), grazed fields (Bharati et al., 2002). The infiltration rates swamp white oak (Q. bicolor Willd.), and bur oak (Q. macrocarpa for components of the riparian buffer were as follows: Michx.) trees. Soil cores (7.6 cm in diam. by 7.6 cm long) were collected silver maple (Acer saccharum Marsh.) Ͼ smooth brome from the treatments from four 10-cm depth increments to determine (Bromus inermis Leyss), timothy (Phleum pretense L.), saturated hydraulic conductivity (K sat), soil water retention, pore-size and Kentucky bluegrass (Poa pratensis L.) grass filter Ͼ distributions, and bulk density. Bulk density was 2.3% lower (P Ͻ 0.05) within the grass and agroforestry buffers compared with the row switchgrass (Panicum virgatum L.). They showed that crop areas. Total porosity and coarse mesoporosity (60-to 1000-m planting buffers can improve infiltration within 8 to diam.) were 3 and 33% higher (P Ͻ 0.05), respectively, for the grass 10 yr. Other studies also have demonstrated that perenand agroforestry buffer treatments than the row crop treatment. The nial vegetation can increase infiltration (Broersma et al., K sat was three and 14 times higher (P Ͻ 0.05) in the grass and agrofores-1995; Wood, 1977). try buffer treatments compared with the row crop treatment. Results Recently, a study was conducted to evaluate the efshow that the grass and agroforestry buffer treatments increased pofects of grass and agroforestry contour buffer strips on tential water storage by 0.90 cm and 1.1 cm per 30-cm depth compared runoff, sediment, and nutrient losses on a claypan soil with the row crop treatment. Although the claypan horizon will domi-(Udawatta et al., 2002). They found that these buffers nate the surface hydrology, buffers may provide some benefit by rereduced surface water runoff, sediment, total P...

Addition of switchgrass (Panicum virgatum) barriers to vegetative filter strips (FS) shows potential as conservation practice. This study evaluates the comparative effectiveness of three conservation practices in reducing runoff, sediment, N, and P losses from 1.5‐ by 16‐m plots on an Aeric Epiaqualf. Three practices compared are a traditional fescue (Festuca arundinacea) filter strip (Fescue‐FS), a switchgrass barrier in combination with the Fescue‐FS (B‐Fescue‐FS) and a switchgrass barrier in combination with a native grass and forbs species filter strip (B‐Native‐FS). This study also predicts transport of sediment, N, and P in Fescue‐FS and B‐Fescue‐FS. Fescue‐FS and B‐Fescue‐FS of equal widths (0.7 m) significantly reduced runoff and sediment transport as compared with a continuous cultivated fallow (CCF) treatment, but B‐Fescue‐FS was more effective for reducing runoff (p < 0.05) and sediment (p < 0.01) transport. B‐Fescue‐FS was also more effective than Fescue‐FS for reducing losses of organic N, NO3–N, NH4–N, particulate P, and PO4–P (p < 0.01). Fescue‐FS and B‐Native‐FS were equally effective for reducing runoff, sediment, and nutrient loss. Effectiveness of FS increased with distance with 18% of runoff, 92% of sediment, and 71% of nutrient leaving the source area being reduced in the first 4 m of the FS. An equation to predict sediment associated with runoff ponding above barriers explained approximately 70% of the variability between measured and predicted values of sediment, organic N, and particulate P transport. Combination of switchgrass barriers with FS is an effective alternative to Fescue‐FS alone for reducing sediment and nutrients in runoff.

A new method for typing single nucleotide polymorphisms in DNA is described. In this method, specific fragments of genomic DNA containing the polymorphic site(s) are first amplified by the polymerase chain reaction (PCR) using one regular and one phosphorothioate-modified primer. The double-stranded PCR product is rendered single-stranded by treatment with the enzyme T7 gene 6 exonuclease, and captured onto individual wells of a 96 well polystyrene plate by hybridization to an immobilized oligonucleotide primer. This primer is designed to hybridize to the single-stranded target DNA immediately adjacent from the polymorphic site of interest. Using the Klenow fragment of E. coli DNA polymerase I or the modified T7 DNA polymerase (Sequenase), the 3' end of the capture oligonucleotide is extended by one base using a mixture of one biotin-labeled, one fluorescein-labeled, and two unlabeled dideoxynucleoside triphosphates. Antibody conjugates of alkaline phosphatase and horseradish peroxidase are then used to determine the nature of the extended base in an ELISA format. This paper describes biochemical features of this method in detail. A semi-automated version of the method, which we call Genetic Bit Analysis (GBA), is being used on a large scale for the parentage verification of thoroughbred horses using a predetermined set of 26 diallelic polymorphisms in the equine genome.

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The effectiveness of stiff‐stemmed grass hedge systems in controlling runoff and soil erosion is influenced by the water transport properties of the soil under grass hedge management. This study evaluated soil hydraulic properties within a grass hedge system 10 yr after establishment. The study was conducted at the USDA‐ARS research station near Treynor, IA in a field managed with switchgrass (Panicum virgatum) hedges. The soil was classified as Monona silt loam (fine‐silty, mixed, superactive, mesic Typic Hapludolls). Three positions were sampled: within the grass hedges, within the deposition zone 0.5 m upslope from the grass hedges, and within the row crop area 7 m upslope from the hedges. Intact soil samples (76 by 76 mm) were taken from the three positions at four depths (100‐mm increments) to determine saturated soil hydraulic conductivity (Ksat), bulk density (ρb), and soil water retention. The grass hedge position had significantly greater (P < 0.05) macroporosity than the row crop and deposition positions in the first two depths and greater than the deposition position in the last two depths. The Ksat within the grass hedge (668 mm h−1) was six times greater than in the row crop position (115 mm h−1) and 18 times greater than in the deposition position (37 mm h−1) for the surface 10 cm. Bulk density and macroporosity were found to provide the best two‐parameter regression model for predicting the log‐transformed Ksat (R2 = 0.68). These results indicate that grass hedges significantly affected soil hydraulic properties for this loess soil.

Saturated hydraulic conductivity (K...) is an essential parameter for understanding soil hydrology. This study evaluated the K... of in situ monoliths and intact cores and compared the results with other studies for Missouri claypan soils. These K... values were used as runoff. model inputs to assess the impact of K... variation on simulated runoff. Lateral in situ K... of the topsoil was determined on 250 by 500 by 230 mm deep monoliths. These values were compared with the K.., of 76 by 76 mm diam. intact cores with and without bentonite to seal macropores. Mean

Planting stiff‐stemmed grass hedges in a watershed may reduce water runoff and soil erosion, in part by altering soil macroporosity. The objective of this study was to characterize macroporosity of soils under a perennial grass hedge system for 12 yr using x‐ray computed tomography (CT) and to compare CT‐macroporosity results with macroporosity estimated from water retention data. Three positions were sampled: grass hedge position, deposition zone position 0.5 m upslope from grass hedges, and row crop position 7 m upslope from the hedges. Intact core samples (76 mm × 76 mm) were collected from two depths, 0 to 100 and 100 to 200 mm, with five replicates per position per depth. Number of pores (macro‐ and meso‐), averaged across depths, in the grass hedge were nearly 2.5 times greater than those in the row crop and five times greater than in the deposition positions; however their circularity was 8.8% lower than in the row crop and 2.6% lower than in the deposition positions. The CT‐measured macroporosity was significantly greater (P < 0.01) for the grass hedge position (0.056 m3 m−3) as compared with the row crop (0.014 m3 m−3) and deposition positions (0.006 m3 m−3). The fractal dimension (D) was significantly greater (P < 0.01) for the grass hedge position (D = 1.56) than in the row crop (D = 1.31) and the deposition (D = 1.12) positions. The values of all measured pore characteristics decreased with depth. Computed tomography‐measured macroporosity data were comparable with macroporosity estimated from water retention data. These findings suggest that grass hedge systems have created more pores and a greater volume of macroporosity.