生态环境用水研究现状、问题分析与基本构架探索

生态学与水文学交叉研究是目前国际上前沿研究领域之一,生态环境用水研究则是连接生态过程与水文过程、刻画生态演化与水资源相互关系的核心问题。对生态、环境用水产生与发展的基本过程进行了回顾,并根据对已有成果的综合分析提出了目前研究中存在的5方面主要问题。首先,生态用水尚需理论上的进一步升华,这一点突出体现在生态用水的概念与内涵表述上;其次,在生态用水研究中,缺乏合理的生态保护目标的建立,因而影响到了研究成果的实际应用价值;第三,目前的研究均是针对较大尺度所作的,不能在生态机理与物理机制上揭示生态用水规律,因此,不适于具体问题的深入分析,个别实验在由“点“尺度向生态用水计算的“面“尺度转换时缺乏基础,从而严重影响了研究成果的精度;第四,生态用水机理是生态用水研究中至为关键的工作,以往研究主要依据野外宏观观测资料来探讨,缺乏直接的实验依据;第五,没有涉及生态用水对生态系统稳定性、生态用水满足程度及其波动性对生态系统影响等方面,从而也使得研究成果的科学性受到影响。同时作者认为,中国工程院“中国可持续发展水资源研究报告“中的生态环境用水概念对我国地大物博,地质地貌与气候类型多样的特点给给予了更多的关注,故可以确定为全国性的生态环境用水概念。最后文章认为应当将生态用水与环境用水分别予以考虑,并给出了其新的概念构架。     

Resistance to water flow in xylem of Picea abies (L.) Karst. trees grown under contrasting light conditions

Summary The relative hydraulic conductivity (k) of xylem and resistance (R) to water flow through trunk, primary roots and branches in Picea abies trees growing under contrasting light conditions were investigated. The xylem permeability to water was measured by forcing 10 mM water solution of KC1 through excised wood specimens. From the values of k, the sapwood transverse area and the length of conducting segments, R of the whole trunk, branches and roots was calculated. The relative conductivity of xylem in open-grown trees exceeded that of shade-grown trees by 1.4–3.1 times, while k was closely correlated with the hydraulically effective radius (R _e) of the largest tracheids (R ² was 0.85–0.94 for open- and 0.51–0.79 for shade-grown trees). Because of both a low k and a smaller sapwood area in shade-grown trees the resistance to water movement through their trunk, roots and branches was many times higher. The distribution of R between single segments of the water-conducting pathway differed considerably in trees from different sites. At high water status the largest share of the total resistance in open- as well as shade-grown trees resides in the apical part of the trunk. The contribution of the branches to total xylem resistance is supposed to increase with developing water deficit.     

Comparison of the effects of botulinum neurotoxin types A and E at the rat neuromuscular junction

Local blockade of transmitter release was produced by s.c. injection of purified botulinum neurotoxin (NT) types A or E above the tibialis anterior muscle of adult male rats. Extensor digitorum longus nerve-muscle preparation was examined for toxin-induced alterations in single twitch and tetanic tension (in situ) or transmitter release (in vitro). For both single twitch and tetanic tension, muscles treated with type E NT recovered from an initial partial paralysis (induced with 56 mouse LD50) or full paralysis (induced with 565 mouse LD50) by 7 days after NT injection, while those treated with only 5 mouse LD50 of type A remained either fully or partially paralysed through 10 days. Also, miniature end-plate potential frequency and mean quantal content were reduced for a longer period of time and/or to a greater extent for muscles treated with type A NT than for those treated with type E. The present results are consistent with the observed higher specific toxicity (i.p. injections in mice) for type A NT than for type E, although these differences may be exaggerated after s.c. injections. The differences in the paralytic effect between types A and E may be determined by differences in amino acid sequence, which causes type E to dissociate more easily from its site of action and/or be detoxified more rapidly. The clinical implications of these findings are discussed.     

X-ray absorption studies of the Zn2+ site of glyoxalase I

X-ray edge and extended absorption fine structure spectra of Zn2+ at the active site of glyoxalase I have been measured. The edge spectrum reveals a simple set of transitions consistent with a 7-coordinate or distorted octahedral Zn2+ model complex. Analysis of the fine structure rules out sulfur ligands to Zn2+ and yields a best fit complex with Zn2+-N (or Zn2+-O) distances of 2.04 and 2.10 A, which are too great for tetrahedral Zn2+ coordination but are appropriate for an octahedral or more highly coordinated complex. Peaks of electron density in the Fourier-transformed region of the higher order shells at distances of 3-4 A from the Zn2+-imidazole model similar to those found with known Zn2+-imidazole model complexes, including carbonic anhydrase [Yachandra, V., Powers, L., & Spiro, T.G. (1983) J. Am. Chem. Soc. 105, 6596-6604], indicating at least two imidazole ligands to Zn2+ on glyoxalase I. Binding of the heavy atom substrate analogue S-(p-bromobenzyl)glutathione did not significantly alter the number of atoms directly bonded to Zn2+ or their distances. No evidence for coordination of the cysteine sulfur of glutathione by the Zn2+ was obtained, and no heavy atom signal from bromine was detected, indicating this atom to be greater than or equal to 4 A from the Zn2+. However, conformational changes of the imidazole ligands of Zn2+ upon binding of the substrate analogue were suggested by changes in the relative intensity of the doublet peaks at 3-4 A from the Zn2+ and assignable to imidazole.(ABSTRACT TRUNCATED AT 250 WORDS)     

西藏冷杉原始林林隙对草本植物和灌木树种多样性的影响

研究了西藏东南部亚高山原始冷杉林林隙对草本植物和灌木树种多样性的影响．结果表明,西藏东南部亚高山原始冷杉林林隙与非林隙林分内草本植物和灌木树种的种类组成、数量、密度和物种多样性均存在较大的差异．由于林隙内光照条件的改善,草本植物和灌木树种更加丰富;林隙内有喜光的草本植物和灌木,也有耐荫性较强的草本植物和灌木,而非林隙林分内仅有耐荫和较耐荫的草本植物和灌木;大部分林隙内的草本植物和灌木树种的物种多样性和均匀度大于非林隙林分;林隙内与非林隙林分的群落相似系数较小,表明林隙与非林隙林分草本植物和灌木群落组成存在差异．林隙大小在174．2～562．2m^2之间,群落相似系数与林隙大小无明显关联．林隙促进了草本植物和灌木树种的繁衍,在维持藏东南亚高山原始冷杉林的物种多样性方面起着重要作用．     

西鄂尔多斯高原干旱荒漠灌木群落空间分布格局及其竞争关系分析

对西鄂尔多斯高原干旱荒漠中的四合木(Tetraena mongolica Maxim. )、霸王(Sarcozygium xanthoxylon Bunge)、白刺(Nitraria tangutorum Bobr. )和红砂[Reaumuria songarica (Pall. ) Maxim. ]优势群落(样方面积50 m×50 m)进行调查,并按土壤中根系分布深度(0～30、30～60、60～90和大于90 cm)将4种灌木分为4个灌木组,运用单变量函数g(t)、标记相关函数markcorr(t)和双变量函数g12(t)对4个灌木组内灌木的空间分布格局及竞争关系进行了研究.g(t)函数和markcorr(t)函数分析结果显示,4个灌木组内的灌木在0～25 m尺度上几乎都呈显著的随机分布,只有根系分布深度在地下0～30 cm的灌木在小于1 m的尺度上呈现均匀分布;除根系分布深度大于90 cm的灌木的标记在12～13 m尺度上呈现较显著的负相关关系外,在0～25 m尺度上每个灌木组间的标记都不相关,表明根系分布深度相似的灌木间无显著的排斥关系,灌木个体的大小不受周围灌木的影响.g12(t)函数分析结果显示,除根系分布深度为0～30与30～60 cm、30～60与60～90 cm的灌木组间分别在某一中小尺度上(3.0～3.5 m、小于1.5 m和7.0～7.5 m)呈现显著的正相关关系外,在0～25 m尺度内根系分布深度相邻的各灌木组间几乎无显著的相关关系,表明根系分布深度不同的灌木间并不互相影响.研究结果表明,在西鄂尔多斯高原干旱荒漠灌木群落中,具有不同生态学特性的灌木分别占据各自的土壤层,呈现出对土壤水分和养分的分层利用,不存在对资源的竞争.     

High pathogenicity of wild-type measles virus infection in CD150 (SLAM) transgenic mice

Measles virus (MV) infection causes an acute childhood disease, associated in certain cases with infection of the central nervous system and development of a severe neurological disease. We have generated transgenic mice ubiquitously expressing the human protein SLAM (signaling lymphocytic activation molecule), or CD150, recently identified as an MV receptor. In contrast to all other MV receptor transgenic models described so far, in these mice infection with wild-type MV strains is highly pathogenic. Intranasal infection of SLAM transgenic suckling mice leads to MV spread to different organs and the development of an acute neurological syndrome, characterized by lethargy, seizures, ataxia, weight loss, and death within 3 weeks. In addition, in this model, vaccine and wild-type MV strains can be distinguished by virulence. Furthermore, intracranial MV infection of adult transgenic mice generates a subclinical infection associated with a high titer of MV-specific antibodies in the serum. Finally, to analyze new antimeasles therapeutic approaches, we created a recombinant soluble form of SLAM and demonstrated its important antiviral activity both in vitro and in vivo. Taken together, our results show the high susceptibility of SLAM transgenic mice to MV-induced neurological disease and open new perspectives for the analysis of the implication of SLAM in the neuropathogenicity of other morbilliviruses, which also use this molecule as a receptor. Moreover, this transgenic model, in allowing a simple readout of the efficacy of an antiviral treatment, provides unique experimental means to test novel anti-MV preventive and therapeutic strategies.     

Dynamics of heart differentiation, visualized utilizing heart enhancer elements of the Drosophila melanogaster bHLH transcription factor Hand

Drosophila melanogaster has become one of the important model systems to investigate the development and differentiation of the heart. After 24h after egg deposition (h AED), a simple tube-like organ is formed, consisting of essentially only two cell types, the contractile cardioblasts and non-myogenic pericardial cells. In contrast to the detailed knowledge of heart formation during embryogenesis, only a few studies deal with later changes in heart morphology and/or function. This is mainly due to the difficulties to carry out whole mount stainings in later stages without complicated dissections or treatments of the cuticle and puparium. In this paper we describe the identification of a hand genomic region, which is fully sufficient to drive GFP expression in heart cells of embryos, larvae, and adults. This serves as an initial step to understand the position of hand in the early regulatory network in heart development. Furthermore, we demonstrate that our newly created GFP reporter line is extremely useful to study postembryonic heart differentiation. For the first time we document heart differentiation in living animals throughout all developmental stages of Drosophila melanogaster, including embryogenesis, all three larval stages, metamorphosis, and the adult life with respect to pericardial cells and cardiomyocytes.     

A short carboxy-terminal domain of polycystin-1 reorganizes the microtubular network and the endoplasmic reticulum

Mutations of PKD1 cause autosomal dominant polycystic kidney disease (ADPKD), a syndrome characterized by kidney cysts and progressive renal failure. Polycystin-1, the protein encoded by PKD1, is a large integral membrane protein with a short carboxy-terminal cytoplasmic domain that appears to initiate multiple cellular programs. We report now that this polycystin-1 domain contains a novel motif responsible for rearrangements of intermediate filaments, microtubules and the endoplasmic reticulum (ER). This motif reveals homology to CLIMP-63, a microtubule-binding protein that rearranges the ER. Our findings suggest that polycystin-1 influences the shape and localization of both the microtubular network and the ER.