植物冷锻炼对于胁强敏感度的影响(英文)

前文由柑桔枝条在不同低温下、不同冷冻时间的电解质外渗测定,提出胁强(stress)、作用时间与胁变(strain)之间关系的数学模型。在这个模型中共有3个参数:屈服点温度(yield point temperature),胁强敏感度(stress sensitivity)和作用时间敏感度(sensitivity to duration),用以描述植物的抗性。抗性强的植物应表现为屈服点温度较低,胁强敏感度或者时间敏感度较低。为验证此数学模型,本工作以经冷锻炼与未经冷锻炼的盆栽柑桔枝条为材料,作不同温度与时间处理的电解质外渗率的测定,研究了冷锻炼对于上述3个参数的影响。发现胁强敏感度和屈服点温度受冷锻炼影响而下降,时间敏感度未表现明显变化。对于田间柑桔、油桐与毛竹的定期测定,在固定冷冻时间下,得到了类似于盆栽柑桔的结果。入冬时,植物抗冻性提高,3种植物都表现出下列两种变化:1.胁强敏感度的明显下降;2.屈服点温度和/或时间敏感度亦下降。开春时的变化则相反。胁强敏感度的变化与后一种变化有各自的规律,且因植物种类而不同。拐点胁强(stress at inflection point)具有与半致死温度(50％killing point temperature)不同的意义,它的变化是上述两种变化的综合结果。本试验结果表明,冷锻炼对于植物胁强敏感度有明显影响,用本数学模型的3个抗性指标描述     

Geometric design improvements for femoral graft-artery junctions mitigating restenosis

The present study is based on the hypothesis that nonuniform hemodynamics, represented by large time-averaged wall shear stress gradients, trigger abnormal biological processes leading to rapid restenosis, i.e. excessive tissue overgrowth and renewed plaque formation, and hence early graft failure. It implies that this problem may be significantly mitigated by finding graft-artery bypass configurations for which the wall shear stress gradient is approximately zero and hence nearly uniform hemodynamics is achieved. These fluid flow and geometric design considerations are applied to four different end-to-side anastomoses for the distal end of a femoral artery bypass with an appropriate test input pulse and a typical 20–80 flow division. A validated finite-volume code has been used to compute the transient three-dimensional velocity vector fields, wall shear stress distributions and surface contours of the wall shear stress gradients. It is shown that large anastomotic flow areas, small continuously changing bifurcation angles, and smooth junction wall curvatures reduce local time-averaged wall shear stress gradients significantly and hence should mitigate restenosis.     

CORRELATED BIOCHEMICAL AND ULTRASTRUCTURAL CHANGES IN NITROGEN-STARVED EUGLENA GRACILIS1

Growth of Euglena gracilis Z Pringsheim under photoheterotrophic conditions in a nitrogen-deprived medium resulted in progressive loss of chloroplastic material until total bleaching of the cells occurred. Biochemical analysis and ultrastructural observation of the first stages of the starvation process demonstrated an early lag phase (from 0 to 9 h) in which cells increased in size, followed by a period of cell division, apparently supported by the mobilization of some chloroplastic proteins such as the photosynthetic CO₂-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. The degradation of the enzyme started after 9 h of starvation and was preceded by a transient concentration of this protein in pyrenoidal structures. Protein nitrogen and photosynthetic pigments as well as number of chloroplasts per cell decreased during proliferation through mere distribution among daughter cells. However, after 24 h, when cell division had almost ceased, there was a slow but steady decline of photosynthetic pigments. This was paralleled by observable ultrastructural changes including progressive loss of chloroplast structure and accumulation of paramylon granules and lipid globules in the cytoplasm. These findings reinforce the role of chloroplastic materials as a nitrogen source during starvation of E. gracilis in a carbon-rich medium. The excess of ribulose-1,5-bisphosphate carboxylase/oxygenase acts as a first reservoir that, once exhausted, is superseded by the generalized disassembly of the photosynthetic structures, if the adverse environment persists more than 24 h.     

DROUGHT STRESS AND INBREEDING DEPRESSION IN LYCHNIS FLOS-CUCULI (CARYOPHYLLACEAE)

Interactions between drought stress and inbreeding depression were studied in Lychnis flos-cuculi. Four inbreeding levels (F = 0, 0.25, 0.50 and 0.75), and three watering treatments were used. Performance was scored for germination rate and proportion, survival, plant size, proportion of plants flowering, flowering date, stem height, number of flowers, flower size, anther weight, fruiting proportion and number of capsules. Multiplicative fitness values were estimated from these traits. Inbreeding affected most of the traits studied, and a severe inbreeding depression was found for the combined fitness estimates. The higher inbreeding depression found here relative to the same family groups in a former experiment may reflect greater dominance and suppression in the present experiment at higher density.     

POLLEN-TUBE COMPETITION AND MALE FITNESS IN HIBISCUS MOSCHEUTOS

The stigmas of animal-pollinated flowers often capture more pollen than is needed to fertilize all available ovules, and mixed-donor pollen loads are probably common. When this is the case, variation in average pollen-tube growth rates can potentially affect the number of seeds sired by a given plant. Despite considerable interest in effects of postpollination processes on male fitness, little is known about the extent of variation in pollen performance among plants from natural populations. To examine this question in Hibiscus moscheutos (rose mallow), we conducted mixed-donor hand-pollination experiments with 39 pollen donors bearing distinctive isozyme markers. Pairs of competing donors were compared on sets of 11 to 15 recipient plants per pair. These donors often differed in the proportions of seeds they sired, with the maximum deviation from an expected ratio of 50:50 being 68:32. Furthermore, three intensively studied plants exhibited consistent trends in relative pollen performance when each was tested against (1) the same three competitors, and (2) groups of 14 competitors chosen at random from the study population. In a separate experiment, we investigated the effects of salinity stress and high soil nutrients on pollen performance. These environmental factors had anticipated effects on leaf production, flower production, and petal length, but style length and (most importantly) the number of seeds sired relative to a standard pollen donor were not affected. In summary, this study provides the strongest evidence to date that pollen-tube competitive ability varies among coexisting plants and may be an important component of male fitness in plants.     

Assessment of the Role of the Glutathione and Pentose Phosphate Pathways in the Protection of Primary Cerebrocortical Cultures from Oxidative Stress

Abstract: Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H₂O₂). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-¹³C₂,6,6-²H₂]glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H₂O₂, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H₂O₂ caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H₂O₂ exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H₂O₂-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H₂O₂ detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.     

Opioid receptors: Some perspectives from early studies of their role in normal physiology,stress responsivity,and in specific addictive diseases

The early history of research on the possible existence of specific opioid receptors and on developing a new form of pharmacotherapy for the treatment of heroin addiction in New York City, from 1960–1973, along with the special relationships between two leading scientists conducting these research efforts, Dr. Eric Simon and Dr. Vincent P. Dole Jr., are presented in a historical perspective. The linkage of these early efforts and the subsequent identification and the elucidation of the effects of exogenous opiates acting at specific opiate receptors in human physiology, including some findings from perspective studies of heroin addicts at time of entry to and during methadone maintenance treatment, are presented in the context of the important clues which thereby were provided concerning the possible roles of the endogenous opioids in normal mammalian physiology. From many of these early clinical research findings and studies in animal models, the hypothesis that the endogenous opioids system may play an important role in stress responsivity was formulated along with the related hypothesis, first presented in the early 1970s, that an atypical responsivity to stress and stressors might be involved in the acquisition and persistence of, and relapse to specific addictive diseases, including heroin addiction, cocaine dependency and alcoholism. More recent studies of the possible involvement of the specific opioid receptors in these three addictive diseases—heroin addiction, cocaine addiction and alcoholism—from our laboratory are discussed in a historical perspective of the development of these ideas from the early research findings of not only Dr. Eric Simon, but his numerous colleagues in opioid research in the United States and throughout the world. Special issue dedicated to Dr. Eric J. Simon.     

肾素－血管紧张素系统──应激激素反应系统

各种急性与慢性应激时,循环血中及脑、心血管、肾腺等组织中血管紧张素Ⅱ（ＡⅡ）显著增多;人剧烈运动后血浆ＡⅡ与皮质醇一样均剧烈增加,在慢性应激性高血压动物循环及组织中,ＡⅡ含量持续地增高。还发现高浓度ＡⅡ对肾上腺糖皮质激素的分泌有直接的刺激作用,而组织ＡⅡ增多又受肾上腺素能β受体的激发。根据近年来的系列工作,并结合文献,我们认为ＡⅡ是一种重要的应激激素;肾素－血管紧张素系统是一个应激激素反应系统;它与经典的应激激素反应系统,下丘脑－垂体－肾上腺皮质系统及交感－肾上腺髓质系统也存在着密切的关系。     

A lea-class gene of tomato confers salt and freezing tolerance when expressed in Saccharomyces cerevisiae

During periods of water deficit, plants accumulate late embryogenesis-abundant (LEA) proteins which are thought to protect cells from stresses associated with dehydration. One of these genes, le25, is expressed in tomato leaves and roots in response to water deficit and abscisic acid accumulation. To study the function of this protein and to test the effect of overproduction of the LE25 protein in Saccharomyces cerevisiae (Sc), a recombinant plasmid in which le25 is expressed under the control of the GAL1 promoter was constructed. The content of LE25 was high in Sc cells transformed with the recombinant plasmid. The transformant exhibited several stress-tolerant phenotypes. Growth of the transformant in a medium with 1.2 M NaCl was improved, as compared to a control strain. While the control strain showed a long lag phase of 40 h, le25-expressing cells showed a shortened lag phase of 10 h. However, no growth improvement was observed in a medium with 2 M sorbitol. In addition, the transformant had an increased survival rate after freezing stress, but not after high-temperature stress. These results, together with its predicted secondary structure, may indicate that LE25 functions as an ion scavenger.     

Biochemical and immunofluorescence analysis of the constitutively expressed HSP27 stress protein in monkey CV-1 cells

The α-crystallin-related stress protein HSP27, which promotes cellular resistance to different types of stress, is constitutively expressed during the growth of several primate tissue culture cells. Here, we report an analysis of the cellular localization of this protein in CV-1 monkey cells. Following cell lysis and fractionation in the absence of detergent about 2 5 % of the cellular content of HSP27 was recovered in the particu late fractions while the remaining of this protein was in the soluble cytoplasmic fraction. This association of HSP27 with particulate fractions was no more observed when cells were lysed in the presence of non-ionic detergent or when cells were pretreated with drugs, such as monensin and colcemid, that disrupt cytoskeletal architecture. Immunofluorescence analysis revealed that HSP27 is concentrated in a polarized perinuclear zone of CV-1 cells from where microtubules radiate. The particular locale of HSP27 was investigated in cells exposed to drugs or treatments, such as monensin, colcemid, cold stess and serum starvation, that disrupt the cellular architecture of microtubules. A correlation was observed between HSP27 cellular locale and microtubules integrity. Our results suggest a possible interaction of a fraction of HSP27 with cytoplasmic organelles or structures, different from the Golgi apparatus, whose distribution depends upon the organization of microtubules.