The Piwi-piRNA pathway provides an adaptive defense in the transposon arms race

Increasingly complex networks of small RNAs act through RNA-interference (RNAi) pathways to regulate gene expression, to mediate antiviral responses, to organize chromosomal domains, and to restrain the spread of selfish genetic elements. Historically, RNAi has been defined as a response to double-stranded RNA. However, some small RNA species may not arise from double-stranded RNA precursors. Yet, like microRNAs and small interfering RNAs, such species guide Argonaute proteins to silencing targets through complementary base-pairing. Silencing can be achieved by corecruitment of accessory factors or through the activity of Argonaute itself, which often has endonucleolytic activity. As a specific and adaptive regulatory system, RNAi is used throughout eukarya, which indicates a long evolutionary history. A likely function of RNAi throughout that history is to protect the genome from both pathogenic and parasitic invaders.     

Use of two spatially explicit models to determine the effect of injury geometry on natural resource recovery

• 1. Disturbance to sessile communities has been evaluated in a wide variety of terrestrial and marine settings, but, to our knowledge, recovery has not explicitly considered the effects of injury shape, except in an exploratory fashion. Therefore, we have developed a simple, but spatially explicit relationship between the geometry of a disturbance and the recovery rate in the context of natural resource damage assessment.
• 2. Here, grounding of motor vessels in shoalgrass (Halodule wrightii), manatee grass (Syringodium filiforme), and turtlegrass (Thalassia testudinum) habitats results in a variety of injury shapes whose recovery must be evaluated to assign penalties and restoration costs to the party responsible.
• 3. We developed two spatially explicit, cellular automata modelling techniques to evaluate injury recovery trajectory. Techniques in both SAS^® and ArcINFO^® were developed and applied to injuries of varying perimeter but fixed area.
• 4. The SAS method utilized either a simple Boolean or probabalistic interrogation of the status of adjacent pixels using the matrix language component of the software. ArcINFO utilized a cost/distance module to evaluate proximity of unfilled to filled (colonized) pixels and then applied a decision rule that governed conversion from unfilled to a filled state. As expected, the greater the perimeter/area ratio, the faster the recovery; and modelling approaches yielded almost identical results.
• 5. A case study involving ～1200 m² of almost monotypic T. testudinum revealed that both models predicted that 100% recovery of above‐ground components of the injury would not occur for approximately 60 years. This model is now being used routinely in the assessment of vessel groundings in seagrass beds within the Florida Keys National Marine Sanctuary and has been used successfully by the Government to prevail in US Federal Court challenges. Both methods have substantial, untapped capabilities to explore the effect of numerous ecological effects on the processes influencing recovery from disturbance.

Published in 2004 by John Wiley & Sons, Ltd.     

Tillage systems and soil properties in east Africa

This paper defines tillage, indicating that as it is mostly a physical concern of the soil, it has not been studied as much as chemically related soil properties. Tillage in shifting cultivation is also reviewed. Different tillage systems in a number of east African Countries namely Tanzania, Malawi, Botswana, Kenya, Zambia and Uganda are reviewed. The types of tillage in their respective soils are discussed in each Country. Uganda's tillage practices for the main food crop (banana) are discussed, pointing out the crop's rooting system in relation to the heavy, relatively fertile soils, where the bananas are mostly grown. The paper distinguishes between tillage to avoid soil compaction and tillage to reduce soil crusting or hardening and concludes that more research should be carried out on tillage practices relating to heavy soils as it affects the different types of crops, as most of the previous tillage research had been carried out on relatively light soils. Soil crusting or hardening which may involve an understanding of the physical, chemical and biological properties of the soil, should also receive more attention.     

Analysis of the Thermal Energy Requirements for the Extraction of Leaf Protein Concentrate from some Green Plants

Extraction of protein from the leaves of green plants is very important because of the high cost of conventional forms of protein such as meat, milk and fish. In order to design machinery for this extraction, and also to embark on leaf protein concentrate extraction, it is necessary to measure and analyse the energy requirements to carry out each process involved in the extraction, using different plant species.Experiments were carried out to determine the amount of crude protein, and the thermal energy required to extract leaf protein concentrate, from juices obtained from the leaves of some plant species. Leaves from the following plants were selected: cassava (Manihot esculanta), Siam weed (Chromolaena odorata), bitter leaf (Vernonia amygdalina), gliricidia (Gliricidia maculata) and thorny tree (Hura crepetans). The leaves from the plant species were macerated in a laboratory pulper. Juice was obtained from the samples using perforated cylinders and a hydraulic press. The specific heat capacity of the juices was determined using the cooling curve method. The values of the heat capacities were used to calculate the amount of thermal energy required to raise the temperature of each juice from its normal temperature of about 25°C to a total protein coagulation temperature of about 80°C. The crude protein content of the extract was determined using the Kjeldal method.Results indicate that the green coagulum extracted from all the juices all have a protein content of at least 37%. The thermal energy required to coagulate protein from the juices ranges from 1·59 kJ kg⁻¹ for Hura crepetans to 2·7 kJ kg⁻¹ for Vernonia amygdalina. The energy requirement to obtain crude protein (CP) ranges from 8 kJ kg⁻¹ [CP] with Hura crepetans to 182 kJ kg⁻¹ [CP] with Vernonia amygdalina. Both results are statistically significant at the 0·01 confidence interval. It is concluded that the choice of plant species can significantly lower the thermal energy requirement for the extraction of leaf protein concentrate.     

Distribution and diversity of wildlife in northern Kenya in relation to livestock and permanent water points

Arid rangelands host a variety of drought-tolerant wildlife species, many of them requiring conservation efforts for the survival of their populations. The development of drinking water sources for people and livestock forms one of the main development interventions in these rangelands. However, the impact of availability of permanent drinking water on wildlife remains unknown. In this study we analyzed the distribution of wildlife and livestock in northern Kenya in relation to distance to permanent water. Livestock were concentrated in areas close to permanent water, while wildlife were frequently farther away from water; their distributions were inversely correlated. In addition, wildlife assemblages were more diverse farther from water. These results suggest that livestock and human activities related to water points negatively affect the distribution of wildlife.     

The role of nitrogen oxides in oxidant production as predicted by the Regional Acid Deposition Model (RADM)

Regional oxidant distributions produced under various atmospheric conditions and emission scenarios are investigated using the Regional Acid Deposition Model (RADM). RADM is a complex, evolving three-dimensional Eulerian model that describes the chemistry, transport and deposition of tropospheric trace species including SO₂, sulfate, NO _x and volatile organic compounds as well as O₃, other major oxidants and acids. The model calculates the short-term temporal evolution of atmospheric trace gas concentrations and their deposition on the regional scale. This study is focused on oxidant production in the eastern United States and southeastern Canada. The influence of atmospheric conditions is explored by comparing three characteristic winter, summer and spring/fall cases. Base-case 1985 emissions of SO _x , NO _x , volatile organic compounds (VOCs), NH₃ and CO are specified using the comprehensive pollutant emissions inventory developed as part of the National Acid Precipitation Assessment Program (NAPAP). The perturbed case, which represents projected anthropogenic emission changes for 2010, indicates changes in daily total 80 km grid average NO _x emissions ranging from increases of 75% to decreases of 45% and VOC emission changes ranging from increases of 65% to decreases of 20%. The largest NO _x emission changes occur in the northeast, and the largest VOC changes occur in the Gulf Coast area. Ground level grid average midday O₃ concentrations for the 1985 emission cases are highest (on the order of 70 to 100 ppb) in the New York City and Houston metropolitan areas for the summer and spring cases; the summer case also indicates relatively high grid average O₃ concentrations of greater than 80 ppb in the southeast. Winter case values are much lower than summer O₃ values throughout the region, with highs of 40 to 50 ppb occurring in the southeast and the Great Lakes area. Changes in NO _x and other emissions under the complex 2010 emissions scenario for the summer case result in maximum O₃ concentration reductions of 10% in the Houston area and increases in O₃ of a few percent in some rural areas of the southeast. This study underscores the need for more comprehensive assessment of the complex relationships among regional emission changes, oxidant production and atmospheric conditions.     

Influence of texture on habitable pore space and bacterial-protozoan populations in soil

Summary Soil texture affects pore space, and bacterial and protozoan populations in soil. In the present study we tested the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils because they have a larger volume of protected pore space available to them. The experiment consisted of three sterilized Orthic Black Chernozemic soils (silty clay, clay loam, and sandy loam) inoculated with bacteria, two treatments (with and without protozoa), and five sampling dates. The soils were amended with glucose and mineral N on day 0. On day 4 bacterial numbers in all three soils were approximately 3×10⁹ g^–1 soil. The greatest reduction in bacteria due to protozoan grazing occurred between day 4 and day 7. Compared to the treatment without protozoa, bacteria in the treatment with protozoa were reduced by 68, 50, and 75% in the silty clay, clay loam, and sandy loam, respectively. On day 4, 2 days after the protozoan inoculation, all protozoa were active. The numbers were 10330, 4760, and 15 380 g^–1 soil for the silty clay, clay loam, and sandy loam, respectively. Between day 4 and day 7, the period of greatest bacterial decline, total protozoa increased greatly to 150480, 96160, and 192100 g^–1 soil for the three soils, respectively. Most protozoa encysted by day 7. In all soils the addition of protozoa significantly increased CO₂–C evolution per g soil relative to the treatment without protozoa. Our results support the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils.     

Antioxidant capacity of some herbs/spices from cameroon: a comparative study of two methods

This study evaluates the antioxidant capacity of 14 herbs/spices from Cameroon. Freeze-dried samples extracted in methanol (free or unconjugated polyphenol) and in 1.2 M hydrochloric acid (HCl) in methanol (total antioxidant that is both unconjugated and conjugated) were analyzed using two different antioxidant assay methods [Folin-Ciocalteu reagent (Folin) and the ferric reducing antioxidant power (FRAP)]. The 1.2 M HCl in methanol extracts had significantly higher (P < 0.001) antioxidant capacities than the methanolic extract. Generally, the FRAP antioxidant values were significantly (P < 0.001) higher than the Folin antioxidant values. Although a significant correlation (P < 0.05) was obtained between the Folin phenol and the FRAP antioxidant, the trends of the antioxidant capacity of the samples were different for the Folin and FRAP methods. The leaves of the Piper species top the total antioxidant tables in both Folin and FRAP assay methods, respectively. Irvingia gabonensis tops the FRAP free antioxidant list, while Piper umbellatum leads the Folin free antioxidant followed by Thymus vulgaris. Thus, the antioxidant capacity of plant samples determined by different methods should be interpreted with caution. However, irrespective of the assay method used, the samples were rich in antioxidants.     

Calibration and prediction of amino acids in stevia leaf powder using near infrared reflectance spectroscopy

The use of stevia as animal feed additive has been researched over the years, but how to rapidly predict its amino acid contents has not been studied yet by using near-infrared reflectance spectroscopy. In the present study, 301 samples of stevia leaf powder were defined as the calibration set from which calibration models were optimized, and the performance of prediction was evaluated. Compared with other mathematical treatments, the models developed with the "1, 12, 12, 1" treatment, combined with modified partial least-squares regression and standard normal variance with de-trending, had a significant potential in predicting amino acid contents, such as threonine, serine, etc. Six spectral regions were found to possess large spectrum variation and show high contribution to calibration models. From the present study, the calibration models of amino acids in stevia were successfully developed and could be applied to quality control in feed processing, breeding selection and mutant screening.