Regulation of blood glucose by hypothalamic pyruvate metabolism

The brain keenly depends on glucose for energy, and mammalians have redundant systems to control glucose production. An increase in circulating glucose inhibits glucose production in the liver, but this negative feedback is impaired in type 2 diabetes. Here we report that a primary increase in hypothalamic glucose levels lowers blood glucose through inhibition of glucose production in rats. The effect of glucose requires its conversion to lactate followed by stimulation of pyruvate metabolism, which leads to activation of adenosine triphosphate (ATP)-sensitive potassium channels. Thus, interventions designed to enhance the hypothalamic sensing of glucose may improve glucose homeostasis in diabetes.     

Structure of a thiol monolayer-protected gold nanoparticle at 1.1 A resolution

Structural information on nanometer-sized gold particles has been limited, due in part to the problem of preparing homogeneous material. Here we report the crystallization and x-ray structure determination of a p-mercaptobenzoic acid (p-MBA)-protected gold nanoparticle, which comprises 102 gold atoms and 44 p-MBAs. The central gold atoms are packed in a Marks decahedron, surrounded by additional layers of gold atoms in unanticipated geometries. The p-MBAs interact not only with the gold but also with one another, forming a rigid surface layer. The particles are chiral, with the two enantiomers alternating in the crystal lattice. The discrete nature of the particle may be explained by the closing of a 58-electron shell.     

Constraints on neon and argon isotopic fractionation in solar wind

To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in 20Ne/22Ne or 36Ar/38Ar values. For 20Ne/22Ne, the difference between low- and high-speed wind components is 0.24 +/- 0.37%; for 36Ar/38Ar, it is 0.11 +/- 0.26%. Our measured 36Ar/38Ar ratio in the solar wind of 5.501 +/- 0.005 is 3.42 +/- 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history.     

Effects of different management practices on the soil–water balance and crop yield for improved dryland farming in the Chinese Loess Plateau

Field experiments were carried out to study the effects of different soil management practices on the water balance, precipitation use efficiency (PUE), and crop yield (i.e. winter wheat and peanut) on a loess soil near Luoyang (east edge of the Chinese Loess Plateau, Henan Province, China). Field plots were set up in 1999 including following soil management practices: subsoiling with mulch (SS), no-till with mulch (NT), reduced tillage (RT), two crops per year (i.e. winter wheat and peanut, TC), and a conventional tillage control (CT). The field plots were equipped to monitor all components of the soil–water balance except evapotranspiration, which was computed by solving the water balance equation. The results showed that although soil management had smaller influence on the magnitude of the water balance components than did precipitation variations, small influences of the applied soil management practices on water conservation during the fallow period can greatly affect winter wheat yield. SS increased consistently precipitation storage efficiency (PSE) and PUE over the 5 years compared to CT except during the wettest year. NT also had a noticeable effect on postharvest water storage during the fallow period; however, the influence on yield of NT depended on the amount of precipitation. TC lowered the winter wheat yield mainly due to the unfavorable soil moisture conditions after growing peanut in summer; however, the harvested peanut gained an extra profit for the local farmer. No matter which kind of soil management practices was adapted, PSE never exceeded 41.6%, which was primarily attributed to high evapotranspiration. From data of five consecutive agricultural years between 2000 and 2005, it could be concluded that SS resulted in the highest PSE, PUE and crop yield. TC also showed promising results considering the economic value of the second crop. NT performed slightly less as SS. CT gave intermediate results, whereas RT was the worst alternative.     

A nitrogen dynamic hydroponic culture on performance and quality of water spinach (Ipomoea aquatica)

Abstract

In view of the unreasonable application of chemical fertilizers in agriculture and the groundwater pollution caused by nitrogen (N) leaching, a nitrogen dynamic hydroponic culture was used to simulate the dynamics variation of ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) in the leaching loss soil. Solutions with different ratio of NO₃-N and NH₄-N (100:0, 70:30, 50:50, 30:70 and 0:100) were prepared as well as the same solutions that not containing NO₃-N .Water spinach was chosen to culture in the two solutions that differ from NO₃-N every two (E2) or five days (E5) to observe the growth, quality and nutrient solution uptake. In terms of the growth, uptake of N source, N use efficiency and the chemical indicators, plants grown in the balanced solution all showed the best results. The nitrogen dynamic hydroponic culture showed some differences between E2 and E5 in some aspects. Under the same N source level, plants in E2 showed a better growth and higher NO₃-N uptake than E5. On the other hand, the uptake of NH₄-N seemed to be affected significantly by the interchanged frequency, which showed the same variations of glutamine synthetase activity. The activity of nitrate reductase and glutamine synthetase showed the coexist of NO₃-N and NH₄-N could play synergistic effect. It is not recommended to supplement NO₃-N frequently in the case of N leaching loss, which has little impact on the growth and may lead to the hard taste and groundwater pollution.     

Effects of a plant parasitic nematode (Heterodera trifolii) on clover roots and soil microbial communities

We studied the effects of the root endoparasitic nematode Heterodera trifolii on rhizodeposition and the root architecture of white clover (Trifolium repens). Rhizosphere solutions were collected from the root systems of plants growing with and without H. trifolii (200 juveniles per inoculated plant) in sand-based microlysimeters. The organic carbon (C) content of these solutions was analyzed, and they were applied to plant-free soils to investigate microbial responses. Although plant biomass was unaffected by nematodes, the architecture of the root systems was significantly altered, with a decrease in overall root length and an increase in the density of lateral branches from the primary root. The presence of nematodes reduced the concentration of organic compounds in the rhizosphere solutions but only on the final sampling date (75 days). Analysis of microbial signature phospholipid fatty acids revealed no change in the structure of the microbial communities in soils to which rhizosphere solutions were applied. However, these microorganisms did respond with changes in substrate utilization patterns (community-level physiological profiles). Microbes in soils that received rhizosphere solutions from the nematode-infected clover showed lower utilization of most substrates but higher utilization of oligosugars. These responses appear to be related to changes in roots and rhizodeposition associated with nematode infection of clover roots. The results of this study suggest that root herbivory can negatively impact carbon-limited soil microbial communities via changes in root architecture that moderate rhizodeposition.     

Dynamics of algal populations and acetylene-reducing activity in five rice soils inoculated with blue-green algae

Summary The dynamics of five inoculated strains of heterocystous blue-green algae (BGA) and indigenous algae were studied for 1 month in 1-m² microplots of five soils previously air-dried or oven-dried. The same soils were then dried and resubmerged for another 2 months to study the effect of controlling algal grazers with neem (Azardirachta indica) seeds on the revival and dynamics of indigenous and inoculated algae. During the month following inoculation, inoculated BGA multiplied to some extend in all soils but never dominated the total algal flora. They rarely dominated the indigeneous heterocystous BGA, and did so only when the growth of N₂-fixing BGA was poor or after the decline of blooms of indigenous strains. Once the soils were dried, two of the five inoculated strains did not reappear. During the 1st month following rewetting, the remaining inoculated strains again exhibited poor growth; however, after 2 months of submergence, inoculated Aulosira fertilissima developed an agronomically significant bloom in neem-treated plots of two soils. Correlations between acetylene-reducing activity and heterocystous BGA populations indicated a major contribution by indigenous BGA and a minor contribution by inoculated BGA to the N₂-fixing activity of the soils during the first experiment and the 1st month of the second experiment. The establishment of inoculated BGA exhibited clear differences among strains but was less affected by the nature of the soil and heat treatment. Neem application might have had a delayed positive effect on the late establishment of inoculated A. fertilissima and favored BGA growth and N₂ fixation by the total algal population.Visiting Scientist at IRRI