A quantitative model of wheat root systems is developed that links the size and distribution of the root system to the capture of water and nitrogen (which are assumed to be evenly distributed with depth) during grain filling, and allows estimates of the economic consequences of this capture to be assessed. A particular feature of the model is its use of summarizing concepts, and reliance on only the minimum number of parameters (each with a clear biological meaning). The model is then used to provide an economic sensitivity analysis of possible target characteristics for manipulating root systems. These characteristics were: root distribution with depth, proportional dry matter partitioning to roots, resource capture coefficients, shoot dry weight at anthesis, specific root weight and water use efficiency. From the current estimates of parameters it is concluded that a larger investment by the crop in fine roots at depth in the soil, and less proliferation of roots in surface layers, would improve yields by accessing extra resources. The economic return on investment in roots for water capture was twice that of the same amount invested for nitrogen capture.
In vivo methylphenidate (MPD) administration increases vesicular monoamine transporter-2 (VMAT-2) immunoreactivity, VMAT-2-mediated dopamine (DA) transport, and DA content in a nonmembrane-associated (referred to herein as cytoplasmic) vesicular subcellular fraction purified from rat striatum: a phenomenon attributed to a redistribution of VMAT-2-associated vesicles within nerve terminals. In contrast, the present study elucidated the nature of, and the impact of MPD on, VMAT-2-associated vesicles that cofractionate with synaptosomal membranes after osmotic lysis (referred to herein as membrane-associated vesicles). Results revealed that, in striking contrast to the cytoplasmic vesicles, DA transport velocity versus substrate concentration curves in the membrane-associated vesicles were sigmoidal, suggesting positive cooperativity with respect to DA transport. Additionally, DA transport into membrane-associated vesicles was greater in total capacity in the presence of high DA concentrations than transport into cytoplasmic vesicles. Of potential therapeutic relevance, MPD increased DA transport into the membrane-associated vesicles despite rapidly decreasing (presumably by redistributing) VMAT-2 immunoreactivity in this fraction. Functional relevance was suggested by findings that MPD treatment increased both the DA content of the membrane-associated vesicle fraction and K ϩ -stimulated DA release from striatal suspensions. In summary, the present data demonstrate the existence of a previously uncharacterized pool of membrane-associated VMAT-2-containing vesicles that displays novel transport kinetics, has a large sequestration capacity, and responds to in vivo pharmacological manipulation. These findings provide insight into both the regulation of vesicular DA sequestration and the mechanism of action of MPD, and they may have implications regarding treatment of disorders involving abnormal DA disposition, including Parkinson's disease and substance abuse.Methylphenidate (MPD) is a commonly prescribed psychostimulant used to treat attention-deficit hyperactivity disorder. It is well established that MPD binds with high affinity to the neuronal dopamine transporter (DAT) where it blocks the inward transport of dopamine (DA) (Wayment et al., 1999;. In addition, MPD indirectly affects DA transport by the vesicular monoamine transporter-2 (VMAT-2), a transporter protein that is responsible for the sequestration of cytoplasmic DA. Specifically, MPD administration increases [ 3 H]DA transport into nonmembrane-associated (referred to herein as cytoplasmic) vesicles purified from lysates of striatal synaptosomes prepared from treated rats (Sandoval et al., 2002(Sandoval et al., , 2003. MPD also increases DA content in the cytoplasmic vesicle subcellular fraction (Sandoval et al., 2002). These phenomena probably result from a redistribution of VMAT-2-containing vesicles within nerve terminals away from membranes and into the cytoplasm (Sandoval et al., 2002).Recent attention has focused on the regulation of cytop...
Investment in precision farming technologies can be expensive and is not expected to be costeffective for every farm. Previous research and farm experience has shown that the amount of soil variability across a farm and within a field is of key importance for determining potential benefits from the adoption of precision farming. The research reported here evaluates the analysis of yield map sequences and electromagnetic induction (EMI) soil sensing as potentially cost-effective methods for identifying and mapping soildetermined ''management zones'' within fields. Both methods are shown to provide useful information for the provisional delineation of soil type boundaries and crop management zones, though soil examination in the field is still necessary to confirm specific soil characteristics.
Expectations of disease prevalence in the case mix during a laboratory observer performance study may systematically affect the behavior of observers in terms of their actual confidence ratings.
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