The Use of a Model to Investigate the Influence of some Environmental Factors on the Growth of Perennial Ryegrass

A modelof thegrasscrop isconstructed, inahichthe simulated valuesof crop morphology and physiology adapt automatically to changesin the environment. The model predicts photosynthesis, partitioningof assimilates and the growth or the cropin terms of leaves,stems and rmts from environmental data and the initial weightsof the crop components following defoliation. The model is usedto investigate the separate effects of light, temperature, canopystructure and maintenance respiration on the growth and denlopmcnt of the crop. It demonstrates how the crop attempts to optimizeaboveground growth, and the complexity of the interaction betweenthe physiological and environmental factors controlling growth. Lolium perenne, perennial ryegrass, photosynthesis, partition of assimilates, mathematical model     

p38 MAPK信号转导途径在关节软骨细胞中的激活和作用

p38信号转导途径是MAPK途径的一种,软骨细胞是关节软骨中唯一的细胞成分。软骨细胞中的p38 MAPK可以被多种细胞因子、机械因素等所激活,它与软骨细胞表型的保持和分化、软骨细胞的肥大化和钙化、凋亡、软骨基质金属蛋白酶的合成、软骨炎性细胞因子的产生等有密切关系,可能在关节炎的发生发展中发挥了重要作用。     

植物次生代谢物对植食性哺乳动物营养和生理生态特征的影响

植物次生代谢物对植食性哺乳动物的营养和生理生态效应是动植物相互关系研究中的一个重要方面。本文简要介绍了植食性哺乳动物处理植物次生代谢物的一般途径,着重阐述了植物次生代谢物对植食性哺乳动物的营养和生理特征的限制方式,并对决定植食性哺乳动物处理植物次生代谢物能力差异性的相关因素进行了探讨。最后,结合国际上的研究趋势,论述了国内开展此类研究的方向和重点。     

Melatonin induces hypertrophy of brown adipose tissue in Spermophilus tridecemlineatus

Nonshivering thermogenesis (NST) plays an important role in hibernators during cold exposure and arousal periods. Brown adipose tissue (BAT), an important site of NST, displays seasonal changes in S. tridecemlineatus while cold exposure and short photoperiods stimulate hypertrophy of BAT.The pineal gland and melatonin have been implicated in thermoregulation but relatively little is known about the pineal's role in hibernation. In this investigation chronic melatonin administration via both silicone rubber implants containing 3 mg of melatonin and daily intraperitoneal injections of saline containing 50 μg of melatonin induced hypertrophy of BAT in young-of-the-year S. tridecemlineatus. Chronic melatonin administration appears to mimic the effects of cold exposure and/or short photoperiods on the hypertrophy of BAT.     

干湿交替和冻融作用对土壤肥力和生态环境的影响

干湿交替和冻融作用对土壤肥力和生态环境的影响朴河春,刘广深,洪业汤（中国科学院地球化学研究所,贵阳５５０００２）ＥｆｆｅｃｔｓｏｆＡｌｔｅｒｎａｔｉｖｅＤｒｙｉｎｇ－ＲｅｗｅｔｔｉｎｇａｎｄＦｒｅｅｚｉｎｇ－ＴｈａｗｉｎｇｏｎｓｏｉｌＦｅｒｔｉｌｉｔ...     

Glucagon-like Peptide-1 (GLP-1) and the Control of Glucose Metabolism in Mammals and Teleost Fish

Glucose metabolism in mammalian species and teleost fish iscontrolled by different metabolic pathways. These include differencesin the function of several major hormones, especially insulinand GLP-1. The major physiological role of GLP-1 in mammalsis to connect the consumption of nutrients with glucose metabolism.The glucose lowering effects of GLP-1 in the postprandial stateof mammals are regulated predominantly through metabolic pathwaysthat integrate different physiological processes. These are:(i) stimulation of insulin release from the pancreatic ß-cellduring hyperglycemia and (ii) inhibition of nutrient absorptionin the gastrointestinal tract. These effects are mediated bya same type of a highly selective GLP-1 receptor, often referredto as the "pancreatic GLP-1 receptor." In teleost fish GLP-1increases glucose levels through the activation of glycogenolysisand gluconeogenesis from liver. Functional characterizationof the recombinant GLP-1 receptor from zebrafish, which is thefirst example of a recombinant fish GLP-1 receptor, demonstratedthat zebrafish GLP-1 receptor has a binding specificity towardsa wider range of GLP-1 structures than the mammalian GLP-1 receptor.This property of the zebrafish GLP-1 receptor, and most likelyother fish GLP-1 receptors, sets apart the structure of thezebrafish GLP-1 receptor from the structures of mammalian GLP-1receptors. These differences in the binding specificity betweenthe zebrafish and mammalian GLP-1 receptors might reflect inpart the differences in the mechanism by which GLP-1 regulatesglucose metabolism in mammals and teleost fish.     

The effect of hormones on Trichomonas vaginalis

The hormonal milieu can alter susceptibility to infection. The effect of hormones on Trichomonas vaginalis was studied utilizing axenically cultured clinical isolates. Oestrogens, in physiological concentrations, decreased the growth of the organisms and their attachment to mammalian cells in vitro, and acted as a chemorepellent. The specificity of these effects was verified by their being blocked with anti-oestrogens, by the dose- and time-dependency of the responses, and by the lack of effect with other hormones. These results suggest that oestrogens may decrease the virulence of T. vaginalis; however, interactions between oestrogens and mammalian cells may promote the development of infection. Thus complicated interactions between hormones, micro-organisms and mammalian cells must determine whether exposure to oestrogens predisposes to or prevents the development of infection.     

The structure and function of adhesive gels from invertebrates

Many marine invertebrates form strong, temporary attachmentsusing viscoelastic gels. To better understand these adhesives,an analysis of what is known of gel structure and function wasperformed. There are different ways of making gels, rangingfrom entangling of giant glycoproteins to crosslinking of smallerproteins. The mechanics of the gel depend largely on the sizeof the polymer, its concentration, and whether it is crosslinked.Compared to gels such as mammalian mucus, the mechanics of adhesivemucous gels often appear to depend more heavily on relativelysmall proteins than on megadalton-sized glycoproteins. In addition,changes in concentration and the presence of specific proteinshave been associated with the change from a non-adhesive toan adhesive form. The attachment strengths produced by differentgels at different concentrations were compared with the changesin attachment strength seen in living animals. These data suggestthat changes in concentration are not sufficient to accountfor adhesion. Thus, it is likely that the changes in proteincomposition may play a large role.     

Responses to Rapid Temperature Change in Vertebrate Ectotherms

Vertebrate ectotherms often encounter rapid, large scale changesin body temperature. In this paper, I discuss the direct effectsof changing body temperature on physiological parameters, aswell as corrective responses initiated by the animal. For manybiological functions, mean body temperature provides a usefulmeasure of the thermal effects produced by an altered environmentaltemperature. Under most conditions, the fins and body surfaceof fish are more important avenues of heat exchange than thegills. The local thermal sensitivity of peripheral blood vesselsresults in vasomotor adjustments which can alter thermal conductivity.Acid-base balance is challenged by changes in body temperature.Shifts in body temperature also alter metabolic demands, enzymeconformation, ionic and osmotic relationships, spontaneous activitylevels and nervous system function. Compensatory mechanismsinclude behavioral thermoregulation, by which animals seek toavoid stressful thermal environments, and autonomic restorativeresponses such as high temperature panting in reptiles. Waterbreathers may initiate anticipatory responses to minimize arterialoxygen fluctuations during termperature change. The organizationof the central neuronal network underlying the above regulatoryresponses is unclear. Both air and water breathers are ableto initiate compensatory acid-base responses, but the strategiesutilized by the two groups are quite different. Altered bodytemperature initiates long-term acclimation responses, and ifrapid, can also trigger stress responses.     

Expression and function of alpha-adrenoceptors in zebrafish: drug effects, mRNA and receptor distributions

The alpha2-adrenoceptors are G-protein-coupled receptors that mediate many of the physiological effects of norepinephrine and epinephrine. Mammals have three subtypes of alpha2-adrenoceptors, alpha2A, alpha2B and alpha2C. Zebrafish, a teleost fish used widely as a model organism, has five distinct alpha2-adrenoceptor genes. The zebrafish has emerged as a powerful tool to study development and genetics, with many mutations causing diseases reminiscent of human diseases. Three of the zebrafish adra2 genes code for orthologues of the mammalian alpha2-adrenoceptors, while two genes code for alpha2Da- and alpha2Db- adrenoceptors, representing a duplicated, fourth alpha2-adrenoceptor subtype. The three different mammalian alpha2-adrenoceptor subtypes have distinct expression patterns in different organs and tissues, and mediate different physiological functions. The zebrafish alpha2-adrenergic system, with five different alpha2-adrenoceptors, appears more complicated. In order to deduce the physiological functions of the zebrafish alpha2-adrenoceptors, we localized the expression of the five different alpha2-adrenoceptor subtypes using RT-PCR, mRNA in situ hybridization, and receptor autoradiography using the radiolabelled alpha2-adrenoceptor antagonist [ethyl-3H]RS-79948-197. Localization of the alpha2A-, alpha2B- and alpha2C-adrenoceptors in zebrafish shows marked conservation when compared with mammals. The zebrafish alpha2A, alpha2Da, and alpha2Db each partially follow the distribution pattern of the mammalian alpha2A: a possible indication of subfunction partitioning between these subtypes. The alpha2-adrenergic system is functional in zebrafish also in vivo, as demonstrated by marked locomotor inhibition, similarly to mammals, and lightening of skin colour induced by the specific alpha2-adrenoceptor agonist, dexmedetomidine. Both effects were antagonized by the specific alpha2-adrenoceptor antagonist atipamezole.     

Effects of urea, trimethylamine oxide, and osmolality on respiration and citrulline synthesis by isolated hepatic mitochondria from Squalus acanthias

The effects of osmolality and of urea and trimethylamine oxide on citrulline synthesis and respiration by isolated hepatic mitochondria from Squalus acanthias (spiny dogfish) were determined. Optimal rates of citrulline synthesis and of respiration, as well as maximal respiratory control ratios, were obtained when the osmolality was about 300 mOsm when physiological concentrations of urea and trimethylamine oxide were present, analogous to mammalian mitochondria. Urea and trimethylamine oxide do not act as osmolytes and do not significantly affect these rates. When glutamate is not saturating, increasing concentrations of urea over the range of concentrations of physiological significance (e.g. 0.1-0.5 M) significantly inhibit citrulline synthesis, but not respiration. This response to urea concentration may reflect a specific homeostatic mechanism for maintaining physiological concentrations of urea.     

Light,puberty, and aggression: A proximal mechanism hypothesis

Rapidly accumulating evidence indicates that light reduces the human pineal's inhibitory effect on the gonads. Artificially extended daily photoperiods, by allowing increased production of gonadal steroids, have probably accentuated the secular growth trend and may be causing males, especially adolescents and young adults, to have an overready hormonal response to situations which elicit aggressive behavior.The author thanks George M. Vaughan, Harry J. Lynch, Mark D. Altschule, Edmund M. Dewan, Solomon H. Katz, George Adelman, John Ott, and Melvin J. Konner for much needed encouragement and edification. Thanks also to Heide Duda and Wesley Taoka (Countway Library, reference desk, Harvard Medical School) for gracious help on so many occasions.     

The effects of ionizing radiation on domestic dogs: a review of the atomic bomb testing era

Dogs were frequently employed as laboratory subjects during the era of atomic bomb testing (1950–1980), particularly in studies used to generate predictive data regarding the expected effects of accidental human occupational exposure to radiation. The bulk of these studies were only partly reported in the primary literature, despite providing vital information regarding the effects of radiation exposure on a model mammalian species. Herein we review this literature and summarize the biological effects in relation to the isotopes used and the method of radionuclide exposure. Overall, these studies demonstrate the wide range of developmental and physiological effects of exposure to radiation and radionuclides in a mid-sized mammal.     

Comparison of glyoxalase I purified from yeast (Saccharomyces cerevisiae) with the enzyme from mammalian sources

Glyoxalase I from yeast (Saccharomyces cerevisiae) purified by affinity chromatography on S-hexylglutathione-Sepharose 6B was characterized and compared with the enzyme from rat liver, pig erythrocytes and human erythrocytes. The molecular weight of glyoxalase I from yeast was, like the enzyme from Rhodospirillum rubrum and Escherichia coli, significantly less (approx. 32000) than that of the enzyme from mammals (approx. 46000). The yeast enzyme is a monomer, whereas the mammalian enzymes are composed of two very similar or identical subunits. The enzymes contain 1Zn atom per subunit. The isoelectric points (at 4 degrees C) for the yeast and mammalian enzymes are at pH7.0 and 4.8 respectively; tryptic-peptide ;maps' display corresponding dissimilarities in structure. These and some additional data indicate that the microbial and the mammalian enzymes may have separate evolutionary origins. The similarities demonstrated in mechanistic and kinetic properties, on the other hand, indicate convergent evolution. The k(cat.) and K(m) values for the yeast enzyme were both higher than those for the enzyme from the mammalian sources with the hemimercaptal adduct of methylglyoxal or phenylglyoxal as the varied substrate and free glutathione at a constant and physiological concentration (2mm). Glyoxalase I from all sources investigated had a k(cat.)/K(m) value near 10(7)s(-1).m(-1), which is close to the theoretical diffusion-controlled rate of enzyme-substrate association. The initial-velocity data show non-Michaelian rate saturation and apparent non-linear inhibition by free glutathione for both yeast and mammalian enzyme. This rate behaviour may have physiological importance, since it counteracts the effects of fluctuations in total glutathione concentrations on the glyoxalase I-dependent metabolism of 2-oxoaldehydes.     

Social contraception in naked mole-rats and marmoset monkeys

This review summarizes some of the recent advances in our understanding of the social suppression of reproduction. The subject is considered mainly at the physiological level in two mammalian species which display social suppression of reproduction to an extreme degree: the eusocial naked mole-rat, Heterocephalus glaber , and the common marmoset monkey, Callithrix jacchus . Such complete social control of reproduction provides useful models to study basic neuroendocrine and physiological mechanisms involved in mammalian reproduction.     

中国哺乳动物生理生态学研究进展与展望

中国哺乳动物生理生态学研究自20世纪50年代始,经过70多年的发展,已系统研究了分布于青藏高原、内蒙古草原、横断山脉等地理分布区的代表性物种的生理适应性,研究主题包括能量代谢和体温调节、冬眠（蛰眠）、水代谢、生态免疫、肠道菌群与宿主的能量代谢和产热调节,研究物种以小型哺乳动物为主。在新时期除了进一步加强对极端环境的生理适应研究外,也需关注大型动物对环境的生理适应,发展新兴领域如保护生理学等,同时要借助多组学技术、同位素技术、遥感技术、红外技术等,加强对动物生理适应的机理性探究。本文回顾了中国哺乳动物生理生态学的发展历程,总结了主要领域取得的重要进展。     

An evolutionarily conserved enzyme degrades transforming growth factor- alpha as well as insulin

A single enzyme found in both Drosophila and mammalian cells is able to selectively bind and degrade transforming growth factor (TGF)-alpha and insulin, but not EGF, at physiological concentrations. These growth factors are also able to inhibit binding and degradation of one another by the enzyme. Although there are significant immunological differences between the mammalian and Drosophila enzymes, the substrate specificity has been highly conserved. These results demonstrate the existence of a selective TGF-alpha-degrading enzyme in both Drosophila and mammalian cells. The evolutionary conservation of the ability to degrade both insulin and TGF-alpha suggests that this property is important for the physiological role of the enzyme and its potential for regulating growth factor levels.     

Light Fluctuations and Photosynthesis

The effects of fluctuating light on photosynthesis are examined.A simple model of leaf photosynthesis is used so that the analysiscan be presented in explicit terms, the time-dependent problemis solved, and the response of photosynthesis to step changesin light-flux density is calculated. The presence of light fluctuationscan cause a discrepancy between measurements and estimates ofphotosynthesis; the relevant factors are the response time ofthe device used for measuring light-flux density, the responsetime of the photosynthetic system in the leaf, and the steady-statelight response curve with the degree of non-linearity and thevalue of the light-flux density for maximum photosynthesis beingespecially important. Some general methods for estimating practicallythe effects of light fluctuations on photosynthesis are described.The use of the methods of time-series analysis in such problemsis discussed.     

The Effect of Temperature on Vegetative Growth in Climatic Races of Dactylis glomerata in Controlled Environments

The growth patterns in two natural populations of Dactylis glomeratafrom contrasting climatic regions, Norway and Portugal, werestudied at four constant temperatures (5, 10, 20, and 30°C) in a 16-h photoperiod. Marked changes in relative growth-rateat different temperatures were positively correlated with changesin both net assimilation rate and leaf-area ratio, whereas differencesbetween the populations in the relative growth-rate were theresult of differences in net assimilation rate, and were negativelycorrelated with differences in leaf-area ratio. The changesin leaf-area ratio at different temperatures were correlatedwith changes in leaf morphology and distribution of assimilateswithin the plant. The possible adaptive advantage of these vegetativegrowth patterns is discussed in relation to the survival ofthe plants in the original environments.