土地利用／覆被变化对土壤质量影响研究进展

土地利用／覆被变化作为人类利用土地各种活动的综合反映,是影响土壤质量变化最普遍、最直接、最深刻的因素。利用与覆被变化体现为：林草地与耕地间的转变、湿地开垦为农田及耕作经营措施、作物轮作制度、施肥等变化,不仅对土壤质量造成了不同程度的影响,而且通过影响气候、土壤、水文以及地貌而对自然环境产生了深刻的影响。文章从土地覆被类型变化、农作物种类变化、土地利用集约度变化等方面,综述了近期取得的研究成果,指出研究中存在的难点及今后研究的重点。     

The β6/β7 region of the Hsp70 substrate-binding domain mediates heat-shock response and prion propagation

Hsp70 is a highly conserved chaperone that in addition to providing essential cellular functions and aiding in cell survival following exposure to a variety of stresses is also a key modulator of prion propagation. Hsp70 is composed of a nucleotide-binding domain (NBD) and substrate-binding domain (SBD). The key functions of Hsp70 are tightly regulated through an allosteric communication network that coordinates ATPase activity with substrate-binding activity. How Hsp70 conformational changes relate to functional change that results in heat shock and prion-related phenotypes is poorly understood. Here, we utilised the yeast [PSI ⁺] system, coupled with SBD-targeted mutagenesis, to investigate how allosteric changes within key structural regions of the Hsp70 SBD result in functional changes in the protein that translate to phenotypic defects in prion propagation and ability to grow at elevated temperatures. We find that variants mutated within the β6 and β7 region of the SBD are defective in prion propagation and heat-shock phenotypes, due to conformational changes within the SBD. Structural analysis of the mutants identifies a potential NBD:SBD interface and key residues that may play important roles in signal transduction between domains. As a consequence of disrupting the β6/β7 region and the SBD overall, Hsp70 exhibits a variety of functional changes including dysregulation of ATPase activity, reduction in ability to refold proteins and changes to interaction affinity with specific co-chaperones and protein substrates. Our findings relate specific structural changes in Hsp70 to specific changes in functional properties that underpin important phenotypic changes in vivo. A thorough understanding of the molecular mechanisms of Hsp70 regulation and how specific modifications result in phenotypic change is essential for the development of new drugs targeting Hsp70 for therapeutic purposes.     

Detection of outliers and level shifts in time series: an evaluation of two alternative procedures

A unified method to detect and handle innovational and additive outliers, and permanent and transient level changes has been presented by R. S. Tsay. N. S. Balke has found that the presence of level changes may lead to misidentification and loss of test‐power, and suggests augmenting Tsay's procedure by conducting an additional disturbance search based on a white‐noise model. While Tsay allows level changes to be either permanent or transient, Balke considers only the former type. Based on simulated series with transient level changes this paper investigates how Balke's white‐noise model performs both when transient change is omitted from the model specification and when it is included. Our findings indicate that the alleged misidentification of permanent level changes may be influenced by the restrictions imposed by Balke. But when these restrictions are removed, Balke's procedure outperforms Tsay's in detecting changes in the data‐generating process. Copyright © 2000 John Wiley & Sons, Ltd.     

A comparative analysis of the cell biology of senescence and aging

Various intracellular organelles, such as lysosomes, mitochondria, nuclei, and cytoskeletons, change during replicative senescence, but the utility of these changes as general markers of senescence and their significance with respect to functional alterations have not been comprehensively reviewed. Furthermore, the relevance of these alterations to cellular and functional changes in aging animals is poorly understood. In this paper, we review the studies that report these senescence-associated changes in various aging cells and their underlying mechanisms. Changes associated with lysosomes and mitochondria are found not only in cells undergoing replicative or induced senescence but also in postmitotic cells isolated from aged organisms. In contrast, other changes occur mainly in cells undergoing in vitro senescence. Comparison of age-related changes and their underlying mechanisms in in vitro senescent cells and aged postmitotic cells would reveal the relevance of replicative senescence to the physiological processes occurring in postmitotic cells as individuals age.     

Ultrastructural differences in mitochondria of skeletal muscle in the prerigor and rigor states.

Loss of cristae and matrix occur in the mitochondria of skeletal muscles prior to any observable changes in myofibrillar proteins during the development of rigor mortis. Care must be observed because ultrastructural changes in mitochondria in some studies may be attributed to a specific trauma, whereas the changes may be due to the lower pH in postmortem muscle.     

The genetic code in mitochondria and chloroplasts

The universal genetic code is used without changes in chloroplasts and in mitochondria of green plants. Non-plant mitochondria use codes that include changes from the universal code. Chloroplasts use 31 anticodons in translating the code; a number smaller than that used by bacteria, because chloroplasts have eliminated 10 CNN anticodons that are found in bacteria. Green plant mitochondria (mt) obtain some tRNAs from the cytosol, and genes for some other tRNAs have been acquired from chloroplast DNA. The code in non-plant mt differs from the universal code in the following usages found in various organisms: UGA for Trp, AUA for Met, AGR for Ser and stop, AAA for Asn, CUN for Thr, and possibly UAA for Tyr. CGN codons are not used by Torulopsis yeast mt. Non-plant mt, e.g. in vertebrates, may use a minimum of 22 anticodons for complete translation of mRNA sequences. The following possible causes are regarded as contributing to changes in the non-plant mt: directional mutation pressure, genomic economization, changes in charging specificity of tRNAs, loss of release factor RF2, changes in RF1, changes in anticodons, loss of lysidine-forming enzyme system, and disappearance of codons from coding sequences.     

Analyzing Macroeconomic Forecastability

This paper estimates, using stochastic simulation and a multi‐country macroeconometric model, the fraction of the forecast error variance of output changes and the fraction of the forecast error variance of inflation that are due to unpredictable asset price changes. The results suggest that between about 25% and 37% of the forecast error variance of output growth over eight quarters is due to asset price changes and between about 33% and 60% of the forecast error variance of inflation over eight quarters is due to asset price changes. These estimates provide limits to the accuracy that can be expected from macroeconomic forecasting. Copyright © 2011 John Wiley & Sons, Ltd.     

Judgmental extrapolation and the salience of change

People may often forecast using cognitive procedures that resemble formal time-series extrapolation models. A model of judgmental extrapolation based on exponential smoothing is proposed in which the setting of the trend parameter is hypothesized to depend upon the relative salience of the successive changes. The salience hypothesis was first tested with exponential series by the use of a framing manipulation. As predicted, focusing the subjects' attention on the changes led to more accurate forecasts. In two investment simulation studies, the salience hypothesis was further examined by varying the statistical properties of the price changes. As predicted, subjects were more likely to sell as prices fell and to buy as prices rose (1) as the sample size of similar changes increased; (2) when the variance of the changes was low; and (3) when the absolute value of the mean change was high. Conditions that may influence judgmental forecasting processes are discussed.     

Seasonal variations of cardiac output in rats.

Cardiac output of rats shows seasonal variations with low values in spring and summer and high ones in autumn and winter. The stroke volume was much more implicated in these changes than the heart rate. The seasonal changes of cardiac output are probably due to changes of thyroid function.     

Ultrastructural differences in mitochondria of skeletal muscle in the prerigor and rigor states

Summary Loss of cristae and matrix occur in the mitochondria of skeletal muscles prior to any observable changes in myofibrillar proteins during the development of rigor mortis. Care must be observed because ultrastructural changes in mitochondria in some studies may be attributed to a specific trauma, whereas the changes may be due to the lower pH in postmortem muscle.Scientific Journal Series, Paper No. 9633, Minnesota Agricultural Experiment Station.     

青藏高原东部暗针叶林采伐迹地土壤环境变化

本文综述目前暗针叶林采伐迹地土壤物理、化学、生物学性质及水土流失情况的研究现状，指出其存在：(1)重点轻面，对生态恢复过程研究不多；(2)重植被调查，而对土壤环境变化研究较少；(3)对迹地生态环境变化机理研究不多等问题，提出迹地生态环境变化研究与生态恢复过程相结合，应展开对采伐迹地影响最大的生态环境因子的地下0．4m和地上1．5m的立体空间层次的综合长期定位研究。     

Hydratation und Sekundärstruktur doppelhelikaler synthetischer Polynukleotide

Summary LD measurements on poly (rA + rU) show a hysteresis of conformational changes within the dehydration-hydration cycle. The different conformational changes of poly (rA + rU) and DNA during hydration are discussed. With poly (rA + rA) no conformational changes could be detected during dehydration.     

从近年科技投入变化看美国科技政策的变化

美国能够成为世界头号科技大国，其科技政策功不可没。近年来，美国不断调整其科技政策以保证站在世界的最前列，这可以从美国在科技中投入的不断变化看出来。本文基于冷战结束至今美国在科技中投入的变化，分析了美国科技政策十几年来的变化特点。     

Oxytocin antagonism of hypothalamic-induced angina-like ECG changes and pressor effects in the cat

Electrical stimulation of a specific site in the lateral hypothalamus of the cat, in a region posterior to Hess' defense area, results in pressor effects and angina-like ECG changes which consist either of T-wave inversion and ST-segment prolongation or in the appearance of tall T-waves. Oxytocin (10 U, i.v.) administered 15 min prior to stimulation, prevents the former ECG changes and BP rise in 90%, and the latter ECG changes and BP rise in 50% of the animals.     

Pathological changes in the heterologous phase of antibasement membrane antibody mediated disease in the rat

Summary The immunological and structural changes during the heterologous phase of experimental antibasement membrane antibody mediated disease was sequentially studied in the rat following single i.v. injections of rabbit antibodies to basement membrane antigens prepared from kidney, lung and salivary gland tissues. Although each of the anti-bodies bound strongly to GBM, structural changes were initially subtle accompanied by proteinuria and hematuria. More severe structural changes related to dose and duration of the disease did not appear for several weeks.     

Unisexual murine schistosomiasis: portal hepatitis in subacute infections

Liver changes induced by unisexual male infection with S. mansoni were studied in mice during 2-20 weeks post-infection, in order to distinguish changes related to released worm substances from changes related to schistosome egg deposition. In subacute unisexual infection the venous wall appears as the target for inflammation which remains focal for a long time and affects limited segments of the main portal veins. Schistosomal pigment deposited in the lobule does not induce inflammatory or fibrogenic reactions.     

Immunomodulation by recombinant human interleukin-8 and its signal transduction pathways in invertebrate hemocytes

We report the presence of interleukin (IL)-8-immunoreactive molecules in hemocytes from the mollusc Mytilus galloprovincialis. Functional studies demonstrate that recombinant human (rh)IL-8 provokes conformational changes, induces chemotaxis, and increases bacterial phagocytic activity in hemocytes. rhIL-8 induces cell shape changes via protein kinase A and C pathways. These morphological changes are followed by reorganization of the actin microfilaments. The findings suggest that, as previously reported for other cytokines, IL-8 is well conserved and deeply involved in immune functions from invertebrates to mammals.     

Effect of nerve stimulation on rat skeletal muscle. A study of plasma membrane

The gastrocnemius muscle of the rat showed no morphological, histometric or plasma membrane changes, after sciatic nerve stimulation with a 5mA current for 30 to 60 min, 10 mA for 30 min and 15 mA for 5 min. However, 10 mA for 60 and 200 min gave rise to mitochondrial and plasma membrane abnormalities. These changes were absent after a rest period. The results indicated that the sciatic nerve stimulation at 10 mA for 60 and 200 min caused reversible changes in the rat skeletal muscle mitochondria and plasma membrane.     

Effect of nerve stimulation on rat skeletal muscle. A study of plasma membrane

Summary The gastrocnemius muscle of the rat showed no morphological, histometric or plasma membrane changes, after sciatic nerve stimulation with a 5 mA current for 30 to 60 min, 10 mA for 30 min and 15 mA for 5 min. However, 10 mA for 60 and 200 min gave rise to mitochondrial and plasma membrane abnormalities. These changes were absent after a rest period. The results indicated the sciatic nerve stimulation at 10 mA for 60 and 200 min caused reversible changes in the rat skeletal muscle mitochondria and plasma membrane.     

Cell density-induced changes in lipid composition and intracellular trafficking

Cell density is one of the extrinsic factors to which cells adapt their physiology when grown in culture. However, little is known about the molecular changes which occur during cell growth and how cellular responses are then modulated. In many cases, inhibitors, drugs or growth factors used for in vitro studies change the rate of cell proliferation, resulting in different cell densities in control and treated samples. Therefore, for a comprehensive data analysis, it is essential to understand the implications of cell density on the molecular level. In this study, we have investigated how lipid composition changes during cell growth, and the consequences it has for transport of Shiga toxin. By quantifying 308 individual lipid species from 17 different lipid classes, we have found that the levels and species distribution of several lipids change during cell growth, with the major changes observed for diacylglycerols, phosphatidic acids, cholesterol esters, and lysophosphatidylethanolamines. In addition, there is a reduced binding and retrograde transport of Shiga toxin in high density cells which lead to reduced intoxication by the toxin. In conclusion, our data provide novel information on how lipid composition changes during cell growth in culture, and how these changes can modulate intracellular trafficking.