Carbon isotope fractionation in tree ring early and late wood in relation to intra-growing season water balance

We determined the stable carbon isotope composition (δ^1.3C) of cellulose extracted from early and late wood in Douglas fir [Pseudotsuga menziexii (Mirb.) Franco] tree rings. Data were obtained for the period 1962 to 1981, at the start of which the trees were 20 years old. A water balance model was used to calculate daily stand transpiration and water deficit. The model incorporates site factors (soil water availability, slope and aspect) and environmental variables (solar radiation, air temperature and rainfall). There was far greater variability in late wood than in early wood δ^1.3C. In wet years, late wood δ^1.3C was significantly lighter (by as much as 2δ) than early wood δ^1.3C but in dry years this difference was reversed. Differences between spring and summer cumulative transpiration accounted for almost 60δ of the variability in differences between early and late wood δ^1.3C. We found excellent correspondence between summer cumulative transpiration and late wood δ^1.3C, with estimates of transpiration accounting for up to 93% of the variability in δ^1.3C. Correlations between early wood δ^1.3C and spring transpiration were generally poor (r2<0.4), but we were able to identify those exceptional years in which there had been a very dry spring. Our results indicate that, while tree ring δ^1.3C correlates reasonably well with basal area increment, it is a far better indicator of inter- and intra-annual variability in water availability than radial growth.     

Perceptual constraints on optimal foraging: The effects of variation among foragers

Summary We present a simple model of habitat selection in which individuals differ in their ability to discriminate between resource sites' profitabilities. The model investigates the effects of violating the ideal assumption of the well-known ideal free distribution (IFD). We show that (1) variability in perceptual limits within a population can significantly change the distribution of foraging animals even though the mean perceptual limit is the same, (2) the direction of this change depends on the proportion of the population that choose randomly between resource sites and (3) better perceivers are more likely to be found at individually more profitable sites, which, because of undermatching with respect to the IFD, are also the absolutely more profitable sites. We note that variability in perceptual limits almost always led to an undermatching of organisms to resources, thereby extending previous workers' results implying that the incorporation of any form of perceptual limits leads to undermatching with respect to the IFD.     

On the existence of stable pairing distributions

We formulate and analyze pair-formation models for multiple groups with general pairing rates and arbitrary mixing probabilities. Under the assumption of constant recruitment rates and equal average duration of all types of partnerships, we have shown that the dynamics are relatively simple because of the monotonicity properties of the dynamical system associated with the pairing/mixing of heterogeneous populations of male and female individuals. In fact, we have shown that the corresponding asymptotic stable paired distribution is given precisely by the asymptotic values of the matrices that prescribe the mixing/contact structure. In other words, if the sizes of the mixing subpopulations of males and females are asymptotically constant and if the average durations of partnerships are about the same regardless of type, then the matrices that describe the mixing between subpopulations also characterize the distribution of paired types. Alternatively, if the distribution of the average duration of relationships between individuals has a large variance then it may be impossible to detect any relationship between the mixing/contact structure and the observed distribution of paired types. The study of models with constant per-capita recruitment rates give rise to homogeneous systems of degree one. The analysis of the dynamics of pairs for models with exponentially growing populations of singles is complicated. So far, we are only able to classify the stability of all non-strictly positive boundary exponential solutions. From our incomplete analysis, it is not possible to detect necessary and sufficient conditions for the existence and stability of strictly interior exponential solutions. We cannot rule out the possibility of oscillations. The mathematical problems associated with the stability of exponential solutions of dynamical systems of degree one are of relevance in demography, epidemiology, and population dynamics.On leave from University of Alabama in Huntsville     

大鼠肝癌模型CBRH—3的建立及其生物学特性

用ＤＥＮＡ诱发近交系Ｗｉｓｔａｒ大鼠,经三个月后得原发性肝癌,移植于同品系幼鼠,从而建立了 一株染色体众数正常,ＡＥＰ阳性的大鼠移植性肝癌模型,命名为ＣＢＲＨ－３,病理鉴定为肝细胞型肝 癌。至今已传至６０余代,目前生长稳定。     

Rat metanephric organ culture in terato-embryology

The development of the permanent mammalian kidney, or metanephros, depends on mesenchymal-epithelial interactions, leading to branching morphogenesis of the ureteric bud that forms the collecting ducts and to conversion of the metanephric mesenchyme into epithelium that forms the nephrons. Rat metanephric organ culture in which these interactions are maintained is a valuable in vitro model system for investigating normal and abnormal renal organogenesis. Methods were designed to evaluate either the capacity of the ureteric bud to branch or that of the mesenchyme to form nephrons. Both are based on specific staining of the ureteric bud and the glomeruli with lectins. Using this approach, we have shown that retinoids are potent stimulating factors of nephrogenesis, acting through an increase in the branching capacity of the ureteric bud. On the other hand, several drugs such as gentamicin and cyclosporin A were found to reduce the number of nephrons formed in vitro. While gentamicin affects the early branching pattern of the ureteric bud, cyclosporin may affect the capacity of the mesencyme to convert into epithelium. This methodology therefore appears a potentially useful tool for toxicological studies new drugs.     

A cellular model for drug interactions on hematopoiesis: The use of human umbilical cord blood progenitors as a model for the study of drug-related myelosuppression of normal hematopoiesis

A cellular model of hematopoiesis which would be more convenient than bone marrow (BM) progenitors and directly relevant to human pathology is needed in order to investigate xenobiotic toxicity. Human umbilical cord blood (HCB), previously shown to be able to repopulate BM, provides a powerful in vitro model of normal human hematopoiesis. In order to validate the use of normal HCB progenitors as targets for dose-related myelosuppression, we used clonogenic assays and expansion in a liquid culture of progenitor-enriched cell suspensions from HCB. A series of 8 reference molecules, doxorubicin, cytosine-arabinoside, 5-fluorouracil, 3-azido-3-deoxythymidine, acetylsalicyclic acid, sodium valproate and two cephalosporin antibiotics, were tested. In vitro 50% inhibition concentrations (IC₅₀) were compared to those observed or reported with BM progenitors, and to the values of plasma concentrations from treated patients. HCB progenitors as in vitro targets for cytotoxic molecules were easy to access and handle, and their use was sensitive, specific and reproducible. They gave results similar to BM progenitors and allowed a qualitative approach to cellular metabolism and toxicity using morphological, flow cytometric and chromatographic methods.Abbreviations ARA-CC cytosine arabinoside - AS acetylsalicylic acid - AZTT 3-azido-3-deoxythymidine - BFUU burst-forming units - BM bone marrow - CFU colony-forming units - DOXX doxorubicin - FU 5-fluorouracil - glyAA glyAcophorin A - HCB human umbilical cord blood - IU international units - PCMEM human placenta-conditioned medium - VA sodium valproate     

Studies on the plant cytoskeleton using miniprotoplasts of tobacco BY-2 cells

Vacuoles in plant cells can be eliminated by centrifugation of protoplasts through a density gradient. In this review, properties of evacuolated protoplasts, named ‘miniprotoplasts’, and the significant roles in plant cytoskeleton studies are described. Miniprotoplasts, prepared from tobacco BY-2 cells whose cell-cycle had been synchronized at late anaphase, continued to divide to form two daughter cells. In the presence of cytochalasin B cytokinetic cleavage was enhanced, suggesting a role of actin filaments in plant cytokinesis. In the cytoplasmic extract of miniprotoplasts both tubulin and actin could be polymerized to form microtubules (MTs) and actin filaments (AFs), respectively. A purification method for tubulin, actin and related proteins was developed using the extract. To investigate the interaction between cortical microtubules and the plasma membrane, an experimental system in which MTs were reconstructed on membrane ghosts was developed by combination of membrane ghosts and the extract.     

Ultra-fastChara myosin: A test case for the swinging lever arm model for force production by myosin

Recent breakthroughs and technological improvements are rapidly generating evidence supporting the “swinging lever arm model” for force production by myosin. Unlike previous models, this model posits that the globular domain of the myosin motor binds to actin with a constant orientation during force generation. Movement of the neck domain of the motor is hypothesized to occur relative to the globular domain much like a lever arm. This intramolecular conformational change drives the movement of the bound actin. The swinging lever arm model is supported by or consistent with a large number of experimental data obtained with skeletal muscle or slime mold myosins, all of which move actin filaments at rates between 1 and 10 μm/sin vitro. Recently myosin was purified, fromChara internodal cells.In vitro the purifiedChara myosin moves actin filaments at rates one order of magnitude faster than the “fast” skeletal muscle myosin. While this ultra fast movement is not necessarily inconsistent with the swinging lever arm model, one or more specific facets of the motor must be altered in theChara motor in order to accommodate such rapid movement. These characteristics are experimentally testable, thus the ultra fast movement byChara myosin represents a powerful and compelling test of the swinging lever arm model.