新疆准噶尔盆地早侏罗世掌鳞杉科植物化石 及古大气CO2浓度

植物化石气孔参数分析是目前恢复古大气二氧化碳浓度较为精准的方法之一,银杏类和松柏类等是恢复古大气CO_2浓度常用的化石类群。本文利用新疆准噶尔盆地下侏罗统三工河组的松柏类掌鳞杉科Brachyphyllum(Hirmeriella?)sp.化石对早侏罗世大气CO_2浓度进行了重建,获得早侏罗世大气CO_2浓度为～1200ppm,丰富了早侏罗世大气CO_2浓度信息,进一步说明掌鳞杉科植物通过气孔比率法在重建侏罗纪大气CO_2浓度方面的可靠性。掌鳞杉科植物的旱生构造和较高的大气CO_2浓度表明早侏罗世Toarcian期大洋缺氧事件在陆地生态系统内可能产生了一定的响应。     

陆生植物气孔参数与大气CO_2浓度变化

陆生植物的起源与演化与全球气候和环境的变化密不可分,利用植物气孔参数(气孔密度和气孔指数)来指示或重建古大气CO2浓度变化是近年来全球变化研究的热点之一。就陆生植物气孔参数的研究进行了概述,对研究中存在的问题及其前景作了简要探讨,并对植物生物学方法在定量研究古气候和古环境变化的趋势进行了分析。     

陆生植物气孔参数与大气CO2浓度变化

陆生植物的起源与演化与全球气候和环境的变化密不可分,利用植物气孔参数(气孔密度和气孔指数)来指示或重建古大气CO₂浓度变化是近年来全球变化研究的热点之一。就陆生植物气孔参数的研究进行了概述,对研究中存在的问题及其前景作了简要探讨,并对植物生物学方法在定量研究古气候和古环境变化的趋势进行了分析。     

气孔参数与大气CO2浓度的相关性及其影响因素

通常认为气孔参数(气孔密度和气孔指数)和大气CO2浓度有负相关关系,但不是每种植物的气孔参数都与CO2浓度的变化有负相关关系,气孔参数对大气CO2浓度的显著反应也只在一定的CO2浓度范围内发生。大气CO2浓度是影响气孔参数变化的主要因素,同时温度、水分的供应和光照条件等其它环境因素也影响气孔参数。CO2浓度和光照条件主要影响气孔发生,而其它环境因素主要影响叶片表皮细胞的大小。气孔指数部分消除了表皮细胞大小带来的影响,用气孔指数指示大气CO2浓度比用气孔密度指示更为可靠。     

CO2倍增对不同氮水平下小麦幼苗根系及叶片NR活性的影响

以小麦品种'小偃22'幼苗为材料,采用开顶式气室和水培实验研究了不同供氮水平(2.5、5.0、10.0和 15.0 mmol·L-1)下小麦幼苗植株生长量、根系形态、有机碳分泌速率和硝酸还原酶(NR)活性对大气CO2浓度升高的响应.结果显示,大气CO2浓度倍增均增加了小麦幼苗各生长阶段根冠生物量以及根系长度、面积、有机碳分泌速率和叶片NR活性.随供氮水平的提高,各生长阶段幼苗根冠生物量、根长和面积以及叶片NR活性呈上升趋势,而有机碳分泌速率呈下降趋势;根冠比变化不同阶段表现不一致,一叶一心期呈下降趋势,二叶一心期和三叶一心期分别以15.0和10.0 mmol·L-1氮水平较高.研究表明,大气CO2浓度升高可促进小麦幼苗根系生长和有机碳分泌速率,提高其氮素同化能力;增加介质供氮有利于高CO2浓度条件下小麦幼苗根冠生长和氮素同化,提高根冠比,减少根系有机碳过度分泌引起的碳损耗.     

两种古海拔重建方法及山旺中中新世古海拔的定量重建

气孔参数法和热力学原理是两种利用植物化石定量重建古海拔的方法。气孔参数法是基于气孔参数与大气CO2浓度的负相关性,而热力学原理则是基于热焓与海拔的负相关性。本文详细介绍这两种古海拔重建方法,并采用热力学原理,结合相关文献资料,定量重建中国山东山旺中中新世的古海拔,结果为400—1000m,高于现代山旺的250m,支持之前共存分析的研究结果。推测自中中新世以来,山旺海拔存在下降的趋势,与中国地貌演变的研究结果吻合。     

气孔导度对CO_2浓度变化的模拟及其生理机制

基于气孔运动的生理生化机制重点进行了气孔导度(gs)对CO2浓度变化的响应机制分析,并推导得到气孔导度(gs)对CO2浓度变化响应模型,并以9种植物进行了模型验证。结果表明:随着CO2浓度的升高,气孔导度会逐渐降低,且下降的幅度会随着CO2浓度的升高而逐渐减弱。气孔导度对CO2浓度(Cs)变化的响应模型可以表达为gs=gmax/(1+Cs/Cs0),其中式中gmax是最大气孔导度和Cs0是实验常数。该模型较好地模拟了气孔导度随CO2浓度变化的规律,模型参数具有明确的生理意义,与Jarvis模型和Ball-Berry模型相比,该模型如何实现多种环境因子的耦合有待进一步突破。另外,模型是在短期改变叶片CO2浓度的条件下得出的,在CO2浓度长期胁迫下的适用性也有待进一步确认。     

绿藻CO2浓缩机制的研究进展

单细胞绿藻是淡水水体中浮游植物的重要组成部分,也是淡水生态系统中主要的初级生产者,其在适应外界CO2浓度变化的过程中,细胞内形成了一种主动转移无机碳的机制－CO2浓缩机制（CO2 concentrating mechanism,CCM）。该机制能使细胞在核酮糖－2－磷酸羧化氧化酶（rubiscol)固碳位点提高CO2浓度,以增加光合作用和减少光吸收。本文综述了这种机制中的无机碳转移模型和不同环境因子（光,温度,CO2浓度和营养水平）对它的调控作用,以期促进深入开展浮游植物对大气CO2浓度升高响应的研究。     

气候变化对森林土壤有机碳贮藏影响的研究进展

森林土壤有机碳库是全球碳循环的重要组成部分,其积累和分解的变化直接影响陆地生态系统的碳贮藏与全球的碳平衡.气候变化将影响植物光合作用及土壤有机碳的分解和转化过程,进而影响森林土壤有机碳贮量及土壤碳动态.温度、降水、大气CO2浓度等气候因子对森林土壤碳贮藏均具有重要影响.了解气候变化对森林土壤有机碳贮藏的影响有助于人们科学管理森林碳库以及进一步寻找缓解气候变化的可行途径.为此,本文综述了森林土壤有机碳贮量的分布以及升温、降水变化和大气CO2浓度升高对森林土壤有机碳贮藏影响的国内外研究进展,并提出了有关的研究展望.     

植物叶片化石气孔参数与古海拔定量重建: 方法与进展

古海拔的定量重建在推演地球动力学模型、大气循环模式、古气候变化以及地球化学循环过程方面都具有十分重要的作用,但是迄今为止在古植物学和古环境研究领域中古海拔的定量重建仍然存在许多难点。本文在介绍目前古海拔定量重建领域几种方法的基础上,重点对植物叶片化石气孔参数及其应用与进展进行了讨论,着重介绍:(1)如何利用植物叶片化石气孔参数法恢复古海拔;(2)方法实践过程中的误差来源与分析;(3)应用实例及展望。     

A control system for arterial blood gases

A system was developed to control arterial O2 and CO2 partial pressure (Pao2, and Paco2) simultaneously and independently of each other. The system makes changes in inspired fractional concentration of O2 and CO2 based on values for end-tidal O2 and CO2 partial pressure. The system was applied in 23 normal subjects. In attempts to maintain a Pao2 of 90 Torr and a Paco2 of 40 Torr, arterial blood gases were 91.1 +/- 6.5 (SD) Torr for Pao2 and 41.2 +/- 3.2 Torr for Paco2. In attempts to maintain a Pao2 of 40 Torr and a Paco2 of 40 Torr, arterial blood gases were 40.4 +/- 3.9 Torr for Pao2 and 38.9 +/- 2.5 Torr for Paco2. In attempts to maintain a Pao2 of 90 Torr and a Paco2 of 55 Torr, arterial blood gases were 98.1 +/- 11.5 Torr for Pao2 and 52.8 +/- 3.4 Torr for Paco2. Coefficients of variations ranged from 7.1 to 11.7% for Pao2 and 6.4 to 7.8% for Paco2.     

酵母2-苯乙醇耐受性的研究进展

2-苯乙醇(2-phenylethanol, 2-PE)是一种可食用且有玫瑰香味的高级芳香醇,常用于食品、化妆品和药品行业。由于物理和化学法制备2-PE得率低,不适用于工业生产。而作为单细胞真核微生物的酵母具有高效合成“天然” 2-PE的潜力,因此酵母作为底盘微生物合成2-PE的策略深受研究者青睐。然而,在酵母进行2-PE发酵过程中不免会受到2-PE毒害作用影响。因此,亟须研究酵母耐受2-PE的机制为生产实际提供理论基础,这也有助于选育具有较高2-PE耐受性的酵母菌株。本文综述了酵母2-PE耐受性的研究进展,从酵母2-PE合成途径、2-PE耐受性机理等方面进行阐述,主要说明提升酵母2-PE耐受性的方法。掌握酵母2-PE耐受机制,最终提升酵母2-PE产量及转化效率是今后研究的重中之重。     

Characterization of a High-Affinity Mg2+-Independent Ca2+-ATPase from Rat Brain Synaptosomal Membranes

A high-affinity Mg2+-independent Ca2+-ATPase (Ca2+-ATPase) has been differentiated from the Mg2+-dependent, Ca2+-stimulated ATPase (Ca2+,Mg2+-ATPase) in rat brain synaptosomal membranes. Using ATP as a substrate, the K0.5 of Ca2+ for Ca2+-ATPase was found to be 1.33 microM with a Km for ATP of 19 microM and a Vmax of 33 nmol/mg/min. Using Ca-ATP as a substrate, the Km for Ca-ATP was found to be 0.22 microM. Unlike Ca2+,Mg2+-ATPase, Ca2+-ATPase was not inhibited by N-ethylmaleimide, trifluoperazine, lanthanum, zinc, or vanadate. La3+ and Zn2+, in contrast, stimulated the enzyme activity. Unlike Ca2+, Mg2+-ATPase activity, ATP-dependent Ca2+ uptake was negligible in the absence of added Mg2+, indicating that the Ca2+ transport into synaptosomal endoplasmic reticulum may not be a function of the Ca2+-ATPase described. Ca2+-ATPase activity was not stimulated by the monovalent cations Na+ or K+. Ca2+, Mg2+-ATPase demonstrated a substrate preference for ATP and ADP, but not GTP, whereas Ca2+-ATPase hydrolyzed ATP and GTP, and to a lesser extent ADP. The results presented here suggest the high-affinity Mg2+-independent Ca2+-ATPase may be a separate form from Ca2+,Mg2+-ATPase. The capacity of Mg2+-independent Ca2+-ATPase to hydrolyze GTP suggests this protein may be involved in GTP-dependent activities within the cell.     

Chromatographic determination of 7,8-methylenedioxy-4H-2,3-benzodiazepin-4-ones in rat plasma: relationship to their anticonvulsant activity

The present investigation was designed to develop an assay suitable for pharmacokinetic studies of new compounds, i.e. the novel 7,8-methylenedioxy-4H-2,3-benzodiazepin-4-one derivatives (2a and 2b), acting as non-competitive AMPA-receptor antagonists. A reversed-phase high-performance liquid chromatographic method has been developed to determine the time-course of plasma concentrations of derivatives 2a and 2b administered intraperitoneally to Sprague-Dawley rats. The separation of compounds studied and a N-methyl-2,3-benzodiazepin-4-one derivative as internal standard (I.S.) from plasma, were carried out by liquid-liquid extraction using diethyl ether. The samples were injected onto the analytical column (Partisil 10 ODS) eluted with acetonitrile/0.01 M acetate buffer (pH 5.3) at a flow-rate of 2 ml/min and detected at 240 nm. Compounds 2a, 2b and I.S. gave retention times of 8.5, 5.25 and 11.1 min, respectively. The selectivity of the method was satisfactory. The mean recovery from spiked rat plasma ranged from 86.7 to 91.6% for 2a, and from 85.1 to 87.0% for 2b. The procedures were validated with a good reproducibility and linear response from 0.0625 to 2 microg/ml, with a regression coefficient of 0.9932 for 2a and 0.9854 for 2b. The lower limit of quantification (LOQ) was taken as 15 ng/ml for the two compounds. 2a and 2b showed no signs of significant degradation in rat plasma during storage at -20 degrees C and following freeze/thaw cycles. Moreover, plasma levels of the tested compounds have been correlated with their anticonvulsant activity, determined in vivo in genetically epilepsy-prone rats. Due to its sensitivity, the method was suitable for application to pharmacokinetic study.     

Calmodulin Stimulation of Ca2+-Dependent ATP Hydrolysis and ATP-Dependent Ca2+ Transport in Synaptic Membranes

We report here characterization of calmodulin-stimulated Ca2+ transport activities in synaptic plasma membranes (SPM). The calcium transport activity consists of a Ca2+-stimulated, Mg2+-dependent ATP hydrolysis coupled with ATP-dependent Ca2+ uptake into membraneous sacs on the cytosolic face of the synaptosomal membrane. These transport activities have been found in synaptosomal subfractions to be located primarily in SPM-1 and SPM-2. Both Ca2+-ATPase and ATP-dependent Ca2+ uptake require calmodulin for maximal activity (KCm for ATPase = 60 nM; KCm for uptake = 50 nM). In the reconstituted membrane system, KCa was found to be 0.8 microM for Ca2+-ATPase and 0.4 microM for Ca2+ uptake. These results demonstrate for the first time the calmodulin requirements for the Ca2+ pump in SPM when Ca2+ ATPase and Ca2+ uptake are assayed under functionally coupled conditions. They suggest that calmodulin association with the membrane calcium pump is regulated by the level of free Ca2+ in the cytoplasm. The activation by calmodulin, in turn, regulates the cytosolic Ca2+ levels in a feedback process. These studies expand the calmodulin hypothesis of synaptic transmission to include activation of a high-affinity Ca2+ + Mg2+ ATPase as a regulator for cytosolic Ca2+.     

A new function and complexity for protein translation initiation factor eIF2B

eIF2B is a multisubunit protein that is critical for protein synthesis initiation and its control. It is a guanine nucleotide exchange factor (GEF) for its GTP-binding protein partner eIF2. eIF2 binds initiator tRNA to ribosomes and promotes mRNA AUG codon recognition. eIF2B is critical for regulation of protein synthesis via a conserved mechanism of phosphorylation of eIF2, which converts eIF2 from a substrate to an inhibitor of eIF2B GEF. In addition, inherited mutations affecting eIF2B subunits cause the fatal disorder leukoencephalopathy with Vanishing White Matter (VWM), also called Childhood Ataxia with Central nervous system Hypomyelination (CACH). Here we review findings which reveal that eIF2B is a decameric protein and also define a new function for the eIF2B. Our results demonstrate that the eIF2Bγ subunit is required for eIF2B to gain access to eIF2•GDP. Specifically it displaces a third translation factor eIF5 (a dual function GAP and GDI) from eIF2•GDP/eIF5 complexes. Thus eIF2B is a GDI displacement factor (or GDF) in addition to its role as a GEF, prompting the redrawing of the eIF2 cycling pathway to incorporate the new steps. In structural studies using mass spectrometry and cross-linking it is shown that eIF2B is a dimer of pentamers and so is twice as large as previously thought. A binding site for GTP on eIF2B was also found, raising further questions concerning the mechanism of nucleotide exchange. The implications of these findings for eIF2B function and for VWM/CACH disease are discussed.     

Structural basis for phosphotyrosine recognition by the Src homology-2 domains of the adapter proteins SH2-B and APS

SH2-B, APS, and Lnk constitute a family of adapter proteins that modulate signaling by protein tyrosine kinases. These adapters contain an N-terminal dimerization region, a pleckstrin homology domain, and a C-terminal Src homology-2 (SH2) domain. SH2-B is recruited via its SH2 domain to various protein tyrosine kinases, including Janus kinase-2 (Jak2) and the insulin receptor. Here, we present the crystal structure at 2.35 A resolution of the SH2 domain of SH2-B in complex with a phosphopeptide representing the SH2-B recruitment site in Jak2 (pTyr813). The structure reveals a canonical SH2 domain-phosphopeptide binding mode, but with specific recognition of a glutamate at the +1 position relative to phosphotyrosine, in addition to recognition of a hydrophobic residue at the +3 position. Biochemical studies of SH2-B and APS demonstrate that, although the SH2 domains of these two adapter proteins share 79% sequence identity, the SH2-B SH2 domain binds preferentially to Jak2, whereas the APS SH2 domain has higher affinity for the insulin receptor. This differential specificity is attributable to the difference in the oligomeric states of the two SH2 domains: monomeric for SH2-B and dimeric for APS.     

An Assembly of Proteins and Lipid Domains Regulates Transport of Phosphatidylserine to Phosphatidylserine Decarboxylase 2 in Saccharomyces cerevisiae

Saccharomyces cerevisiae uses multiple biosynthetic pathways for the synthesis of phosphatidylethanolamine. One route involves the synthesis of phosphatidylserine (PtdSer) in the endoplasmic reticulum (ER), the transport of this lipid to endosomes, and decarboxylation by PtdSer decarboxylase 2 (Psd2p) to produce phosphatidylethanolamine. Several proteins and protein motifs are known to be required for PtdSer transport to occur, namely the Sec14p homolog PstB2p/Pdr17p; a PtdIns 4-kinase, Stt4p; and a C2 domain of Psd2p. The focus of this work is on defining the protein-protein and protein-lipid interactions of these components. PstB2p interacts with a protein encoded by the uncharacterized gene YPL272C, which we name Pbi1p (PstB2p-interacting 1). PstB2p, Psd2, and Pbi1p were shown to be lipid-binding proteins specific for phosphatidic acid. Pbi1p also interacts with the ER-localized Scs2p, a binding determinant for several peripheral ER proteins. A complex between Psd2p and PstB2p was also detected, and this interaction was facilitated by a cryptic C2 domain at the extreme N terminus of Psd2p (C2-1) as well the previously characterized C2 domain of Psd2p (C2-2). The predicted N-terminal helical region of PstB2p was necessary and sufficient for promoting the interaction with both Psd2p and Pbi1p. Taken together, these results support a model for PtdSer transport involving the docking of a PtdSer donor membrane with an acceptor via specific protein-protein and protein-lipid interactions. Specifically, our model predicts that this process involves an acceptor membrane complex containing the C2 domains of Psd2p, PstB2p, and Pbi1p that ligate to Scs2p and phosphatidic acid present in the donor membrane, forming a zone of apposition that facilitates PtdSer transfer.     

Theoretical analysis of effects of blood substitute affinity and cooperativity on organ oxygen transport.

Hemoglobin-based O(2) carriers (HBOCs), which are developed as an alternative to blood transfusion, provide O(2) delivery. At present, there is no model to predict the O(2) transport for a red blood cell-HBOC mixture on a whole organ basis. On the basis of the first principles of mass balance, a model of O(2) transport for an organ was derived to calculate venous Po(2) (Pv(O(2))) for a given inlet arterial Po(2) (Pa(O(2))), blood flow, and oxygen consumption. The model was validated by using several in vivo animal studies on HBOC administration for a wide range of HBOC oxygen-binding parameters and predicted Pv(O(2)) for various Pa(O(2)) in the same species. The model was also used to predict the effect of HBOC affinity and cooperativity on Pv(O(2)) for humans. The results indicate that Pv(O(2)) can be increased at a constant blood flow-to-oxygen consumption ratio by reducing the affinity of HBOC for normoxia and mild hypoxia; however, a high-affinity HBOC would be more efficient in maintaining higher Pv(O(2)) for severe hypoxia (Pa(O(2)) < 40 Torr).