Dietary α-Linolenic Acid Increases the Biosynthesis of the Choline Glycerophospholipids from [14C]CDPcholine in Rat Liver and Kidney But Not in Brain

The effect of feeding rats for 30 days with diets containing high levels of linoleic acid (sunflower oil, SO) or -linolenic acid (perilla oil, PO) was studied in the liver, kidney and brain. The PO group showed a higher labeling of choline glycerophospholipids (CGP) in liver and kidney but no difference with the SO group in ethanolamine glycerophospholipids (EGP) labeling. The brain displayed the lowest incorporation of both precursors and no difference between the two diets. Analyses of brain CGP and EGP fatty acid compositions showed that in the PO group the ratio n-6/n-3 was lower than in the SO group, mainly as a consequence of lower levels of n-6 fatty acids. The mole % of docosahexaenoate (DHA) in these lipids was the same for both groups and only triacylglycerols (TAG) displayed a higher DHA. Therefore, at least in the brain, the magnitude of fatty acid changes observed in CGP and EGP for the PO group does not affect the uptake/incorporation of the precursors into phospholipids.     

A case study of mother-son transfer in mountain gorillas

In mountain gorillas (Gorilla g. beringei), male immigration in bi-sexual units is rare. This paper presents the case of a nearly weaned male infant gorilla who followed his mother in her transfer. This case was recorded in the study population at the Kariske Research Center in 1988. The data come from observation in Group B (on 12 days just prior to the transfer and on 54 days after the transfer over a period of 6 months). The situation of the infant did match the conditions in which infanticide occurs in gorillas, but he was not killed, despite receiving male aggression and being wounded twice. In fact, both the mother and the infant received male aggression more frequently than the long term residents in the group. The aggression received by the mother decreased after she mated with the males and after she weaned the infant. The aggression received by the infant, however, did not decrease after his mother mated with the males, and increased in intensity. The infant reacted fearfully to male aggression, in marked contrast to his mother, who reacted either with indifference, or by simply avoiding the males. The aggression eventually stopped, and the infant became a blackback in Group B. Evolutionarily, the death of the infant would not have markedly accelerated the mother's return to estrus, but the death of the infant could still have benefitted the males, by decreasing the reproductive output of a competitor. Adult male gorillas are also presumably selected to resist male immigration. Proximately, the aggression directed towards the infant was not related to mating access to the mother. The sex of the infant may contribute to explain the post-transfer male aggression, but data on the integration of old female infants in a new group is needed to test whether the sex of the infant has an effect on their vulnerability to infanticide. Also, the intense fear displayed by the infant may have played a role in prompting male aggression.     

Fluorescence decay of pyrene in small and large unilamellar L,α-Dipalmitoylphosphatidylcholine vesicles above and below the phase transition temperature

The fluorescence decays of pyrene in small and large unilamellar L,-dipalmitoylphosphatidylcholine vesicles have been investigated as a function of probe concentration and temperature. When the molar ratio of pyrene to phospholipid equals 1:3000, no excimer emission is observed and the fluorescence decays are mono-exponential. When this ratio is equal to or higher than 1:120, excimer formation is observed.Above the phase transition temperature the observed fluorescence decays of monomer and excimer can be adequately described by a bi-exponential function. The monomer decays can be equally well fitted to a decay law which takes into account a time-dependence in the probe diffusion rate constant. The fluorescence decay kinetics are compatible with the excimer formation scheme which is valid in an isotropic medium. The excimer lifetime and the (apparent) rate constant of excimer formation have been determined as a function of probe concentration at different temperatures above the phase transition temperature. The activation energy of excimer formation is found to be 29.4±1.3 kJ/mol. In small unilamellar vesicles the diffusion constant associated with the pyrene excimer formation process varies from 8.0x10^-7 cm²/s at 40°C to 2.2x10^-6 cm²/s at 70°C.Below the phase transition temperature the monomer decays can be described by a decay law which takes into account a time dependence of the rate constant of excimer formation. The lateral diffusion coefficient of pyrene calculated from the decay fitting parameters of the monomer region varies from 4.0x10^-9 cm²/s at 20°C to 7.9x10^-8 cm²/s at 35°C. No significant difference could be observed between the pyrene fluorescence decay kinetics in small and large unilamellar vesicles.Abbreviations SUV small unilamellar vesicles - LUV large unilamellar vesicles - DPPC dipalmitoylphosphatidylcholine - DMPC dimyristoylphosphatidylcholine - FRAP fluorescence recovery after photobleaching Part of this research has been presented at the 5th international symposium on surfactants in solution. Bordeaux, July 9th–13th 1984     

Studies on metabolic role of 5′-methylthioadenosine in Ochromonas malhamensis and other microorganisms

Several compounds containing a thiomethyl group were found to replace vitamin B₁₂ in a protozoan, Ochromonas malhamensis. The order of the effectiveness was as follows: 5-methylthioadenosine > S-adenosylmethionine > 5-methylthioribose > L-methionine. A similar order was obtained with respect to the permeability of these compounds into the protozoan cells, except for S-adenosylmethionine. 5-Methylthioadenosine and 5-methylthioribose as well as l-methionine markedly increased the intracellular content of l-methionine. The level of S-adenosylmethionine was also increased by them, but to a lesser degree. The thiomethyl group of the compounds was established to be incorporated into S-adenosylmethionine. The metabolic fate of the thiomethyl group of 5-methylthioadenosine cannot be distinguished from that of l-methionine. A high activity of 5-methylthioadenosine nucleosidase was detected in the cell-free extracts of the protozoan. These results strongly suggest that 5-methylthioadenosine would be metabolized to l-methionine via 5-methylthioribose and then the l-methionine would be converted to S-adenosylmethionine. Like l-methionine and vitamin B₁₂, 5-methylthioadenosine and 5-methylthioribose may play an important role in maintenance of the C-1 pool in Ochromonas malhamensis.Neither 5-methylthioadenosine nor 5-methylthioribose replaced vitamin B₁₂ in some vitamin B₁₂-requiring bacteria. This result is consistent with the fact that neither compounds was significantly taken up by these bacteria.Abbreviations MTA 5-methylthioadenosine - AdoMet S-adenosylmethionine - MTR 5-methylthioribose - TCA trichloroacetic acid Paper II in the series. The first paper of the series has been published (Sugimoto and Fukui, 1974)     

Partitioning of water resources among plants of a lowland tropical forest

Source water used by plants of several species in a semi-evergreen lowland tropical forest on Barro Colorado Island, Panama, was assessed by comparing the relative abundance of deuterium, D, versus hydrogen, H (stable hydrogen isotope composition, D) in xylem sap and in soil water at different depths, during the dry season of 1992. Ecological correlates of source water were examined by comparing xylem water D values with leaf phenology, leaf water status determined with a pressure chamber, and rates of water use determined as mass flow of sap using the stem heat balance method. Soil water D values decreased sharply to 30 cm, then remained relatively constant with increasing depth. Average D values were-13, for 0–30 cm depth and-36.7 for 30–100 cm depth. Soil water D values were negatively associated with soil water content and soil water potential. Concurrent analyses of xylem water revealed a high degree of partitioning of water resources among species of this tropical forest. Xylem water D of deciduous trees (average=-25.3±1.4) was higher than that of evergreen trees (average=-36.3±3.5), indicating that evergreen species had access to the more abundant soil water at greater depth than deciduous species. In evergreen shade-tolerant and high-light requiring shrubs and small trees, D of xylem water was negatively correlated with transpiration rate and leaf water potential indicating that species using deeper, more abundant water resources had both higher rates of water use and more favorable leaf water status.     

Evidence for a synergistic salt-protein interaction -- complex patterns of activation vs. inhibition of nitrogenase by salt

The molybdenum nitrogenase enzyme system, comprised of the MoFe protein and the Fe protein, catalyzes the reduction of atmospheric N(2) to NH(3). Interactions between these two proteins and between Fe protein and nucleotides (MgADP and MgATP) are crucial to catalysis. It is well established that salts are inhibitors of nitrogenase catalysis that target these interactions. However, the implications of salt effects are often overlooked. We have reexamined salt effects in light of a comprehensive framework for nitrogenase interactions to offer an in-depth analysis of the sources of salt inhibition and underlying apparent cooperativity. More importantly, we have identified patterns of salt activation of nitrogenase that correspond to at least two mechanisms. One of these mechanisms is that charge screening of MoFe protein-Fe protein interactions in the nitrogenase complex accelerates the rate of nitrogenase complex dissociation, which is the rate-limiting step of catalysis. This kind of salt activation operates under conditions of high catalytic activity and low salt concentrations that may resemble those found in vivo. While simple kinetic arguments are strong evidence for this kind of salt activation, further confirmation was sought by demonstrating that tight complexes that have previously displayed little or no activity due to the inability of Fe protein to dissociate from the complex are activated by the presence of salt. This occurs for the combination Azotobacter vinelandii MoFe protein with: (a) the L127Delta Fe protein; and (b) Clostridium pasteurianum Fe protein. The curvature of activation vs. salt implies a synergistic salt-protein interaction.     

Presence and abundance of CENP-B box sequences in great ape subsets of primate-specific α-satellite DNA

CENP-B, a highly conserved centromere-associated protein, binds to -satellite DNA, the centromeric satellite of primate chromosomes, at a 17-bp sequence, the CENP-B box. By fluorescence in situ hybridization (FISH) with an oligomer specific for the CENP-B box sequence, we have demonstrated the abundance of CENP-B boxes on all chromosomes (except the Y) of humans, chimpanzee, pygmy chimpanzee, gorilla, and orangutan. This sequence motif was not detected in the genomes of other primates, including gibbons, Old and New World monkeys, and prosimians. Our results indicate that the CENP-B box containing subtype of -satellite DNA may have emerged recently in the evolution of the large-bodied hominoids, after divergence of the phylogenetic lines leading to gibbons and apes; the box is thus on the order of 15–25 million years of age. The rapid process of dispersal and fixation of the CENP-B box sequence throughout the human and great ape genomes is thought to be a consequence of concerted evolution of -satellite subsets on both homologous and nonhomologous chromosomes.Correspondence to: T. Haaf     

基于生态地理分区的大兴安岭植被物候时空变化

植被与气候的关系十分密切,植被物候可作为全球气候变化的指示器.大兴安岭位于我国最北部,对气候变化较为敏感,研究该区植被物候的时空变化对评估全球变化对陆地生态系统的影响具有重要意义.依据中国生态地理区划图,将大兴安岭划分为4个生态研究区域,本文利用GIMMS NDVI 3g遥感数据集分析1982—2012年大兴安岭整体及各生态地理分区植被物候变化.结果表明: 研究期间,所有分区植被生长季开始日期均表现为提前趋势,生长季结束日期均表现为推迟趋势.植被物候对气候因子变化敏感,尤其是对气温的敏感程度高于降水,其中,北段山地落叶针叶林区植被生长季开始日期与春季温度呈显著负相关;除南段草原区外,其他3个分区植被生长季结束日期均与秋季降水呈显著负相关.从整体来看,植被物候随海拔、纬度的变化趋势明显.     

古尔班通古特沙漠固定沙丘上白梭梭和梭梭的空间分布及种间关联性

为了探讨沙漠中固沙灌木种群共存和演替机制, 本文基于古尔班通古特沙漠东南缘固定沙丘上白梭梭(Haloxylon persicum)和梭梭(H. ammodendron)种群的地理位置和生长发育阶段信息(幼株、营养株、生殖株和死株), 采用点格局分析方法(g(r)函数)及Monte-Carlo随机模拟检验和零模型选取的方法, 分析了固沙灌木白梭梭和梭梭种群不同生长发育阶段在0-20 m尺度内的空间分布格局及种间关联性。结果表明: (1)两个种群在研究尺度范围内呈聚集分布, 随着尺度的增大, 其聚集强度逐渐减弱; (2)两个种群整体上呈负关联关系, 尺度越大负关联关系越显著; (3)白梭梭种群生长发育阶段相差越大, 个体间正关联关系越显著; 梭梭种群生长发育阶段越接近, 个体间正关联关系越显著; (4)两个种群中龄级较大的个体(如营养株、生殖株和死株)会对对方种群中龄级较小的幼株产生一定的抑制作用; 同时, 随着两个种群中个体的成长, 双方受到的抑制作用逐渐减弱, 主要表现为正关联和无关联。总体而言, 古尔班通古特沙漠固定沙丘白梭梭和梭梭种群的分布格局整体上为聚集分布, 随龄级增加聚集性减弱, 受生境异质性和扩散限制的影响明显。种间关系多为负相关, 种内不同生长发育阶段之间均为正关联关系。     

Transformation of Kluyveromyces lactis with the kanamycin (G418) resistance gene of Tn903

Direct selection of Kluyveromyces lactis resistant to the antibiotic G418 following transformation with the kanamycin resistance gene of Tn903 required the development of a procedure for producing high yields of viable spheroplasts and for the isolation of autonomous replication sequences (ARS). To obtain high yields of viable spheroplasts, cells were treated with (1) a thiol-reducing agent (L-cysteine), and (2) a high concentration of an osmotic stabilizer, 1.5 M sorbitol. Several ARS-containing plasmids were selected from a K. lactis recombinant DNA library in K. lactis and in Saccharomyces cerevisiae. Two of four ARS clones selected in K. lactis promoted transformation frequencies of 5-10 X 10(2) G418-resistant cells/micrograms of plasmid DNA. This frequency of transformation was at least twice as high as with ARS clones selected in S. cerevisiae. The stability of ARS-containing plasmids varied; after 20 generations of growth in the presence of G418, 16-38% of the cells remained resistant to the drug. In the absence of selection pressure less than 5% of the cells retained the drug-resistance phenotype. Plasmids containing the ARS1 or 2 mu replicon of S. cerevisiae failed to transform K. lactis for G418 resistance. Inclusion of S. cerevisiae centromere, CEN4, in a K. lactis ARS recombinant plasmid did not increase the stability of the plasmid in K. lactis, and marker genes on the vector segregated predominantly 4-:0+ through meiosis. We conclude that neither the ARS sequences or the centromere of S. cerevisiae was functioning in K. lactis.