浙江紫金牛属一新变型——黄果朱砂根

报道了发现于浙江苍南县的紫金牛属一新变型--黄果朱砂根(Ardisia crenata Sims f.xanthocarpa F.Y.Zhang et G.Y.Li),该新变型果实为黄色,而原变型为鲜红色.     

The N-terminal region of the starch-branching enzyme from Phaseolus vulgaris L. is essential for optimal catalysis and structural stability

Starch-branching enzymes (SBEs) play a pivotal role in determining the fine structure of starch by catalyzing the syntheses of alpha-1,6-branch points. They are the members of the alpha-amylase family and have four conserved regions in a central (beta/alpha)8 barrel, including the catalytic sites. Although the role of the catalytic barrel domain of an SBE is known, that of its N- and C-terminal regions remain unclear. We have previously shown that the C-terminal regions of the two SBE isozymes (designated as PvSBE1 and PvSBE2) from kidney bean (Phaseolus vulgaris L.) have different roles in branching enzyme activity. To understand the contribution of the N-terminal region to catalysis, six chimeric enzymes were constructed between PvSBE1 and PvSBE2. Only one enzyme (1Na/2Nb)-II, in which a portion of the N-terminal region of PvSBE2 was substituted by the corresponding region of PvSBE1, retained 6% of the PvSBE2 activity. The N-terminal truncated form (DeltaN46-PvSBE2), lacking 46 N-terminal residues of PvSBE2, lost enzyme activity and stability to proteolysis. To investigate the possible function of this region, three residues (Asp-15, His-24, and Arg-28) among these 46 residues were subjected to site-directed mutagenesis. The purified mutant enzymes showed nearly the same K(m) values as PvSBE2 but had lower V(max) values and heat stabilities than PvSBE2. These results suggest that the N-terminal region of the kidney bean SBE is essential for maximum enzyme activity and thermostability.     

Truncated tyrosine kinase B brain-derived neurotrophic factor receptor directs cortical neural stem cells to a glial cell fate by a novel signaling mechanism

During development of the mammalian cerebral cortex neural stem cells (NSC) first generate neurons and subsequently produce glial cells. The mechanism(s) responsible for this developmental shift from neurogenesis to gliogenesis is unknown. Brain-derived neurotrophic factor (BDNF) is believed to play important roles in the development of the mammalian cerebral cortex; it enhances neurogenesis and promotes the differentiation and survival of newly generated neurons. Here, we provide evidence that a truncated form of the BDNF receptor tyrosine kinase B (trkB-t) plays a pivotal role in directing embryonic mouse cortical NSC to a glial cell fate. Expression of trkB-t promotes differentiation of NSC toward astrocytes while inhibiting neurogenesis both in cell culture and in vivo. The mechanism by which trkB-t induces astrocyte genesis is not simply the result of inhibition of full-length receptor with intrinsic tyrosine kinase activity signaling. Instead, binding of BDNF to trkB-t activates a signaling pathway (involving a G-protein and protein kinase C) that induced NSC to become glial progenitors and astrocytes. Thus, the increased expression of trkB-t in the embryonic cerebral cortex that occurs coincident with astrocyte production plays a pivotal role in the developmental transition from neurogenesis to gliogenesis. Our findings suggest a mechanism by which a single factor (BDNF) regulates the production of the two major cell types in the mammalian cerebral cortex.     

Structural characterization of zinc-deficient human superoxide dismutase and implications for ALS

Over 130 mutations to copper, zinc superoxide dismutase (SOD) are implicated in the selective death of motor neurons found in 25% of patients with familial amyotrophic lateral sclerosis (ALS). Despite their widespread distribution, ALS mutations appear positioned to cause structural and misfolding defects. Such defects decrease SOD's affinity for zinc, and loss of zinc from SOD is sufficient to induce apoptosis in motor neurons in vitro. To examine the importance of the zinc site in the structure and pathogenesis of human SOD, we determined the 2.0-A-resolution crystal structure of a designed zinc-deficient human SOD, in which two zinc-binding ligands have been mutated to hydrogen-bonding serine residues. This structure revealed a 9 degrees twist of the subunits, which opens the SOD dimer interface and represents the largest intersubunit rotational shift observed for a human SOD variant. Furthermore, the electrostatic loop and zinc-binding subloop were partly disordered, the catalytically important Arg143 was rotated away from the active site, and the normally rigid intramolecular Cys57-Cys146 disulfide bridge assumed two conformations. Together, these changes allow small molecules greater access to the catalytic copper, consistent with the observed increased redox activity of zinc-deficient SOD. Moreover, the dimer interface is weakened and the Cys57-Cys146 disulfide is more labile, as demonstrated by the increased aggregation of zinc-deficient SOD in the presence of a thiol reductant. However, equimolar Cu,Zn SOD rapidly forms heterodimers with zinc-deficient SOD (t1/2 approximately 15 min) and prevents aggregation. The stabilization of zinc-deficient SOD as a heterodimer with Cu,Zn SOD may contribute to the dominant inheritance of ALS mutations. These results have general implications for the importance of framework stability on normal metalloenzyme function and specific implications for the role of zinc ion in the fatal neuropathology associated with SOD mutations.     

河西走廊植物群落特征及其与气候的关系初探

对河西走廊荒漠植物的群落类型、盖度、密度、重要值、地上生物量等进行了调查,收集整理各区域的气候资料,对它们的关系进行了初步研究。结果显示:(1)物种种类组成、总密度与海拔、经度呈正相关,与纬度呈负相关,在走廊的东南→西北方向上呈递减趋势。(2)在活动积温(>10℃)>3 200℃的荒漠地区,灌木(包括半灌木)在群落中占有绝对优势,其重要值可达到100;当活动积温在3 000℃左右时,群落往往是一些过渡类型,或以草本为优势种、以半灌木或灌木为伴生种,或以半灌木为优势种、以多年生草本为伴生种。(3)在年降水量110 mm以上的荒漠地区,植物群落生活型主要为半灌木或多年生草本;在年降水量110 mm以下的地区,生活型主要为小灌木或一年生草本;在年降水量小于50 mm的极端干旱地区,只有在雨季时有一年生草本生长。表明荒漠生态系统植被稀疏,生物量小,对气候因子,特别是降水变化敏感,对其保育显得尤为重要。     

生物沥滤污泥土地利用适用性分析

研究了污泥生物沥滤对重金属(Cu、Pb和Zn)形态、营养物质和SO42-存在形式的影响,分析生物沥滤污泥土地利用的适用性。结果表明:生物沥滤后,污泥上清液中重金属通过固液分离而去除,污泥中Cu、Pb和Zn的去除率分别为84.1%、34.8%和80.0%,残存于污泥中的重金属含量大幅降低,且生物有效性低,提高了污泥土地利用的安全性。污泥经生物沥滤后氮、磷和钾的流失分别为38.2%、52.1%和42.8%,但仍能保持较好的肥效。采用X-射线衍射光谱分析发现,残留于污泥中的SO24-主要与Ca2 相结合,较为稳定,生物沥滤后的污泥施用于土地后对环境影响较小。     

金佛山自然保护区中国种子植物特有属

在野外调查和数量系统分析的基础上,对金佛山自然保护区的中国种子植物特有属进行了研究。结果表明,金佛山自然保护区分布有中国种子植物特有属51个,占该区种子植物属总数的4·59%,占全国同类属数的20·99%,其中裸子植物4属4种,被子植物4属65种。在被子植物中,双子叶植物占41属58种;单子叶植物占6属7种。在51个特有属中,单种属有39属,占总数的76·47%。唇形科、苦苣苔科、伞形科、兰科含特有属较多约占本区同类属的31·37%。特有属的生活型以多年生草本和落叶木本为主,两者共4属,占特有属总数的80·39%。特有属的分布区类型以东部和中部特有分布为主,并具有少量的南部特有分布成分,51个特有属的分布区类型表明了该区系由热带性质向温带性质的过渡性特征。本区的特有属植物多分布于低山和中山。金佛山与大巴山、武陵山、神农架关系较为密切,它们同属于川东-鄂西特有现象中心(或三峡中心)。在51个中国种子植物特有属中古特有属和珍稀濒危物种占有较大的比例,本区无疑是古植物区系的重要避难所。     

杭州湾潮滩表层沉积物中磷的分布、赋存形态及生态意义

对杭州湾潮滩表层沉积物样品中的磷进行了总量、形态分级提取及生物有效性分析.结果表明:沉积物中总磷的含量为595.5～1268.8μg·g-1,空间分布特征总体表现为杭州湾北岸＞钱塘江杭州河段＞杭州湾南岸.总磷中有89.3%以无机磷形式存在,钙磷、残留无机态磷、有机磷和铁铝结合态磷是沉积物中磷的主要赋存形态,平均分别占总磷的68.3%、14.6%、10.7%和5.3%.钙磷的分布受到盐度变化影响,自钱塘江河口向外海方向明显增加;铁铝结合态磷则相反,分布朝外海逐步递减.沉积物中的潜在生物有效磷(BAP)含量为43.62～177.84 μg·g-1,平均含量为94.13 μg·g-1.该地区与国内典型的河口和滨岸带潮滩比较,总磷处于相对较高水平.强烈的水动力作用及咸淡水交汇使得环境因子频繁变化,加大了沉积物中磷作为内源向上覆水体释放及造成水体富营养化的可能性.     

HIV/AIDS in Asia： The Shape of Epidemics and Their Molecular Epidemiology

The Asia-Pacific region is a home to 60% of the population in the world and to approximately one quarter of people with HIV/AIDS. Close to a million of people has been infected and a half million people died of AIDS annually in Asia,becoming the second largest epicenter of global AIDS epidemic. Molecular epidemiology has been useful tool to track a course of HIV spread. In-depth knowledge from the studies on molecular epidemiology elucidates the dynamics of HIV spread and the interrelationship of epidemics in the different regions in Asia.     

土壤不同水分条件对长春花(Catharanthus roseus)生活史型的影响

为了研究土壤中不同水分条件对长春花生活史型形成及生理代谢的影响,设置对照、轻度干旱、中度干旱和重度干旱等土壤水分梯度,对长春花(Catharanthus roseus(L.)G.Don)幼苗进行处理。对长春花形态指标进行聚类分析发现选择的20个聚类实体被分为2组,第1组为对照(CK)和轻度干旱(LD)处理的植株,第2组为中度干旱(MD)和重度干旱(HD)处理的植株。运用主成分分析(Principal component analysis,PCA)方法对不同土壤水分条件下长春花营养生长(Vegetative growth,V)、有性生殖(Sexual reproduction,S)和无性繁殖(Clone reproduction,C)等3类15种性状进行统计。结果显示,长春花在对照条件下生活史型为V0.39S0.54C0.07,轻度干旱为V0.36S0.50C0.14,中度干旱为V0.53S0.27C0.20,重度干旱为V0.45S0.09C0.46,干旱程度加强显著提高了无性繁殖的比重,降低了有性生殖的比例。同时,对长春花中文朵灵、长春质碱和脱水长春碱等生物碱的含量进行了动态测定,发现重度干旱下的文朵灵、长春质碱和脱水长春碱的含量在16d时分别是对照水平的1.5倍、2.3倍和3.1倍,表明干旱胁迫诱导生物碱积累,为长春花高效栽培提供了理论依据。