树干CO_2释放速率影响因素研究进展

树干CO2释放速率(stemCO2effluxrate,FCO2)是森林生态系统碳循环的重要组成部分,其占树木自养呼吸的14%～48%。对FCO2影响因素进行分析,对于了解全球碳循环以及森林生态系统对全球变暖的响应具有重要意义。本文综述了生物因素和非生物因素对FCO2的影响,指出这些因素不仅直接或间接影响FCO2,而且各因素间还存在交互作用,此外,各因素的影响程度也会随时间、空间而变化。在此基础上,本文提出了今后研究应集中在以下几方面:(1)运用有效方法分离树干释放CO2的各个组分,并分析各个组分与影响因素的关系,深入揭示FCO2变化机制;(2)加强生物、非生物因素交互影响FCO2动态模型的研究,用以提高模拟的准确性;(3)深入探讨FCO2的温度适应性。     

Belowground carbon cycling in a humid tropical forest decreases with fertilization

Only a small fraction of the carbon (C) allocated belowground by trees is retained by soils in long-lived, decay-resistant forms, yet because of the large magnitude of terrestrial primary productivity, even small changes in C allocation or retention can alter terrestrial C storage. The humid tropics exert a disproportionately large influence over terrestrial C storage, but C allocation and belowground retention in these ecosystems remain poorly quantified. Using mass balance and ¹³C isotope methods, we examined the effects of afforestation and fertilization, two land-use changes of large-scale importance, on belowground C cycling at a humid tropical site in Hawaii. Here we report that in unfertilized plots, 80% of the C allocated belowground by trees to roots and mycorrhizae was returned to the atmosphere within 1 year; 9% of the belowground C flux was retained in coarse roots and 11% was retained as new soil C. The gains in new soil C were offset entirely by losses of old soil C. Further, while fertilization early in stand development increased C storage in the litter layer and in coarse roots, it reduced by 22% the flux of C moving through roots and mycorrhizae into mineral soils. Because soil C formation rates related strongly to rhizosphere C flux, fertilization may reduce an already limited capacity of these forests to sequester decay-resistant soil C.     

Root border cells take up and release glucose-C

BACKGROUND AND AIMS: Border cells are released from the root tips of many plant species, and can remain viable in the rhizosphere for 1 week. Whether border cells are capable of controlled glucose exchange with their environment was investigated. METHODS: Border cells were removed from Zea mays L. root tips, and immersed in (14)C-labelled D-glucose. In one experiment, the hexose transport inhibitor, phlorizin, was used to investigate active glucose uptake from a range of glucose concentrations. In another experiment, glucose efflux from border cells was monitored over time. KEY RESULTS: Glucose uptake by the border cells increased with increasing glucose concentration from 0.2 to 20 mm. At 0.2 mm glucose, uptake was mainly active, as evidenced by the approx. 60 % inhibition with phlorizin. At 2 and 20 mm glucose, however, uptake was mainly via diffusion, as phlorizin inhibition was negligible. Glucose efflux increased with time for live border cells in both 2 and 20 mm glucose. There was no clear efflux/time pattern for heat-killed border cells. CONCLUSIONS: Border cells actively take up glucose, and also release it. Under our experimental conditions, glucose uptake and efflux were of similar order of magnitude. In the rhizosphere net glucose exchange will almost certainly depend on local soil conditions.     

北京典型树种木质组织碳释放速率温度敏感性的时间变化规律和铅锤分异特征

采用红外气体分析法(IRGA)于2014年1—12月原位测定了北京市4个典型树种(国槐Sophora japonica,旱柳Salix matsudana,华北落叶松Larix principis-rupprechtii和侧柏Platycladus orientalis)在不同高度上的木质组织CO_2通量速率(E_(CO_2)),旨在比较不同树种间E_(CO_2)及其温度敏感性(Q_(10))的时间变化规律和铅锤分异特征。研究结果显示:(1)4个树种的E_(CO_2)均表现为单峰型季节变化规律,生长月份内的E_(CO_2)显著高于非生长月份,温度和枝干的径向生长是影响E_(CO_2)季节变化的主要因素;(2)E_(CO_2)对温度的敏感性在夏季月份明显降低,且出现明显的垂直分异:Q_(10)随测量高度的增加而增加,呈现出非连续的阶梯分布;(3)在日间尺度上,阔叶树种E_(CO_2)对温度的感性系数Q_(10)出现昼夜不对称现象,晚上Q_(10)明显升高。准确量化E_(CO_2)的时间变化规律和铅锤分异特征,细化不同时间尺度下E_(CO_2)对温度的响应特征,成为准确估算木质组织碳排放的前提条件。     

Cell specific expression of three genes involved in plasma membrane sucrose transport in developingVicia faba seed

Summary In developing seeds ofVicia faba, transfer cells line the inner surface of the seed coat and the juxtaposed epidermal surface of the cotyledons. Circumstantial evidence, derived from anatomical and physiological studies, indicates that these cells are the likely sites of sucrose efflux to, and influx from, the seed apoplasm, respectively. In this study, expression of an H⁺/sucrose symporter-gene was found to be localised to the epidermal-transfer cell complexes of the cotyledons. The sucrose binding protein (SBP) gene was expressed in these cells as well as in the thin-walled parenchyma transfer cells of the seed coat. SBP was immunolocalised exclusively to the plasma membranes located in the wall ingrowth regions of the transfer cells. In addition, a plasma membrane H⁺-ATPase was most abundant in the wall ingrowth regions with decreasing levels of expression at increasing distance from the transfer cell layers. The observed co-localisation of high densities of a plasma membrane H⁺-ATPase and sucrose transport proteins to the wall ingrowths of the seed coat and cotyledon transfer cells provides strong evidence that these regions are the principal sites of facilitated membrane transport of sucrose to and from the seed apoplasm.Abbreviations BCIP 5-bromo-4-chloro-3-indolyl phosphate - DIG digoxigenin - H⁺-ATPase plasma membrane H⁺-translocating adenosine triphosphatase - Ig immunoglobulin - LeSUT1 tomato H⁺/sucrose symporter - SBP sucrose binding protein     

染料木素对MRSA外排蛋白表达的影响

[目的] 研究染料木素对耐甲氧西林金黄色葡萄球菌（MRSA）外排蛋白的影响。[方法] 通过联合药敏实验检测染料木素影响MRSA对环丙沙星的敏感性;利用等重同位素多标签相对定量蛋白质组学（iTRAQ）技术,检测染料木素作用MRSA41577后菌体蛋白表达量的变化;通过生物信息学方法对差异显著的蛋白进行系统分析;通过qPCR和尼罗红外排实验,探讨耐药相关的蛋白介导细菌耐药的作用机制。[结果] 联合药敏实验结果显示,染料木素能增强MRSA对环丙沙星的敏感性;通过iTRAQ技术检测到差异显著蛋白共有129个,包括60个表达上调的蛋白和69个表达下调的蛋白;生物信息学分析结果显示,与细菌耐药相关的蛋白约有14个,其中,通过主动外排系统介导细菌耐药的蛋白主要有PstB、PstS等;qPCR结果显示,与对照组相比,PstB、PstS的基因表达量分别下降了51.6%和78.6%;尼罗红外排实验结果显示,染料木素与尼罗红之间存在竞争关系,为MRSA41577的竞争性抑制剂。[结论] 染料木素可通过降低MRSA41577外排基因pstB和pstS的mRNA表达量,进而影响PstB、PstS外排蛋白的表达来逆转细菌耐药;此外,染料木素还是MRSA41577的竞争性外排抑制剂,可通过与底物竞争外排的方式,使抗菌药物留在菌体内发挥抗菌作用。     

细菌对消毒剂抗性机理研究进展

消毒剂通过抑制膜的主动运输、抑制微生物的代谢、扰乱微生物的DNA复制、使微生物细胞裂解而导致胞内成分渗漏以及使胞内物质凝结等方面发挥灭菌作用.消毒剂在杀灭细菌和控制细菌污染方面具有重要作用,但细菌对消毒剂也会产生抗性.细菌对消毒剂的抗性机制主要通过形成生物被膜,阻挡或外排机制减少消毒剂分子进入细胞,使消毒剂分子失活,以及其他表型性耐药等4个途径来实现,其中通过形成生物被膜阻止消毒剂分子进入细菌细胞或在进入细胞前使消毒剂失去效用,在细菌对消毒剂的抗性机制中具有重要作用.以实际污染的主要菌株为对象,研究它们对常用消毒剂的抗性机制,对控制细菌污染具有极大的应用价值和现实意义.     

春、秋季节树干温度和液流速度对东北3树种树干表面CO2释放通量的影响

为探明温度与液流速度对树干表面CO2释放通量的影响,采用红外气体分析法(IRGA)原位连续测定白桦、兴安落叶松和水曲柳树干表面CO2释放通量,同时测定树干液流速度及树干温度。3树种树干CO2释放通量和液流速度在昼夜变化和季节变化上有一定规律,春、秋季节树干表面CO2释放通量昼夜动态均呈明显的单峰型曲线,但是峰值出现的时间有所区别: 6月份树干表面CO2释放通量峰值出现在夜间,温度峰值则在白天;9月份树干表面CO2 释放通量和液流速度及树干温度在昼夜间的变化规律总体上呈相同趋势,均为白天升高,晚上降低,呈单峰曲线,峰值基本在中午出现。3树种树干表面CO2释放通量有明显的季节性规律,即6月份的CO2释放通量明显高于9月份。9月份和6月份白桦、兴安落叶松和水曲柳的日平均树干表面CO2释放通量分别为0.82,3.32μmol m-2 s-1;0.74,3.78μmol m-2 s-1和1.98,4.98μmol m-2 s-1;6月份和9月份日平均液流速度分别为2.48,10.02g?cm-2?h-1;4.78,10.71g?cm-2?h-1和2.69-7.93g?cm-2?h-1。树干表面CO2释放通量与树干温度和液流速度相关关系显著,6月份和9月份树干表面CO2释放通量与树干温度均呈正相关;树干表面CO2释放通量与液流速度间的相关关系6月与9月不同,6月份液流速度与树干表面CO2释放通量呈负相关,而9月份呈正相关。实验发现,除落叶松外,同1株树24小时周期内水曲柳和白桦液流上升期和下降期液流速度对树干表面CO2 释放通量的影响不一致,可能是由于上下午之间温度不同,导致树干内部CO2溶解度不同,使上下午树干内部CO2与表面通量的平衡发生改变,这种改变存在种间差异,表明温度和液流的共同作用影响树干CO2释放通量。水曲柳月份间树干表面CO2释放通量的差异受液流速度影响较大,白桦和兴安落叶松树干表面CO2释放通量的月份间变化则是液流速度和温度的共同作用的结果。我们的结论是,温度是影响树干呼吸速率的关键因子,但树干呼吸产生的CO2向大气的释放也同时受树干液流速度的影响。温度与液流对春秋季节3树种树干表面CO2释放通量的影响有所不同。     

MsrA Efflux Pump Inhibitory Activity of Piper cubeba L.f. and its Phytoconstituents against Staphylococcus aureus RN4220

MsrA, an efflux pump belonging to ATP‐binding cassette (ABC) transporter family that conferred resistance to macrolides, was detected in Staphylococcus aureus strains. Herein, we report the isolation of phytoconstituents from Piper cubeba fruit methanol extract and investigated their efflux pump inhibitory potential against S. aureus MsrA pump. Four isolated compounds, viz. pellitorine, sesamin, piperic acid and tetrahydropiperine studied in combination with erythromycin in S. aureus RN4220, exhibited 2–8‐fold reduction in minimum inhibitory concentration (MIC) of erythromycin. Pellitorine and sesamin decreased MIC of erythromycin by 8‐fold. The real‐time fluorometry‐based efflux and accumulation studies of ethidium bromide (EtBr) on S. aureus RN4220 in the presence of these compounds showed reduced efflux and enhanced uptake, thus indicating inhibition of the efflux pump. Pellitorine showed significant post‐antibiotic effect of erythromycin. The results revealed that the primary mechanism of action of these compounds involves steady ATP production impairment.