巴山松天然林生物量和生产力的研究

 经测定分析陕西南部28—37年生巴山松天然林的生物量和净初级生产量,结果表明,林分乔木层生物量为81.28t／ha,草本下木生物量为1.45t／ha,林分凋落物量为11.16t／ha;乔木层净初级生产量为6.94t／ha·yr,约45%分配到树叶。巴山松林的消光系数平均为0.33。在地上部生产结构方面,枝重主要集中在树冠中、下部,叶龄愈大,叶重在树冠下部的比例愈高。巴山松林木的根系总长度约99.4km／ha,其中细根占58%。     

Evidence forCis- andTrans-acting element coevolution of the 2-μm circle genome inSaccharomyces cerevisiae

Summary We compared the DNA sequence of the yeas 2-μm plasmidcis-actingSTB andtrans-actingREP1 partition loci of laboratory haploid and industrial amphiploid strains. Several industrial strains had a uniqueSTB sequence (type 1) sharing only 70% homology with laboratorySTB (type 2). Type 1 plasmids had a REP1 protein with 6–10% amino acid substitutions when compared to REP1 of type 2 plasmids. All 2-μm variants that shared a similarSTB consensus sequence exhibited a high degree ofREP1 nucleotide and amino acid sequence conservation. These observations suggest molecular coevolution oftrans-acting elements with cognate target DNA structure. Based on DNA sequencing and Southern hybridization analyses, we classified 2-μm variants into two main evolutionary lineages that differ atSTB as well asREP1 loci. The role of molecular coevolution in yeast intra- and interspecies plasmid evolution was discussed.     

溶液流动对等电溶菌酶晶体生长的影响

本文对等温自由生长和强制性溶液生长的等电溶菌酶的晶体形态进行了研究,发现这些形态变化与溶液相的流动密切相关,指出生物晶体生长停止是由于生长晶体周围的溶质贫乏造成的;通过某些手段减薄或消除这一溶质贫乏区,就可以保证晶体的持续生长。本文的研究对改善大尺寸晶体的生长提供了一条途径。     

应用地理信息系统模拟森林景观动态的研究

根据地理信息系统的结构,通过数据文件的转换,把它与森林动态模型有机地结合起来,可实现对森林景观动态的模拟和预测。这种模拟方法的数据输入灵活,运行速度快,尤其是它可以获得一些以各种图表的形式输出的模拟结果。本文用文字和框图详细描述了地理信息系统的组成与结构,及森林动态模型的选择与运行方式,并以长白山森林景观为例,叙述了这种模拟方法的整个过程。     

Spatial and temporal patterns of intracellular calcium in colonic smooth muscle

Summary Intracellular calcium [Ca²⁺] _i measurements in cell suspension of gastrointestinal myocytes have suggested a single [Ca²⁺] _i transient followed by a steady-state increase as the characteristic [Ca²⁺] _i response of these cells. In the present study, we used digital video imaging techniques in freshly dispersed myocytes from the rabbit colon, to characterize the spatiotemporal pattern of the [Ca²⁺] _i signal in single cells. The distribution of [Ca²⁺] _i in resting and stimulated cells was nonhomogeneous, with gradients of high [Ca²⁺] _i present in the subplasmalemmal space and in one cell pole. [Ca²⁺] _i gradients within these regions were not constant but showed temporal changes in the form of [Ca²⁺] _i oscillations and spatial changes in the form of [Ca²⁺] _i waves. [Ca²⁺] _i oscillations in unstimulated cells (n = 60) were independent of extracellular [Ca²⁺] and had a mean frequency of 12.6 +1.1 oscillations per min. The baseline [Ca²⁺], was 171 ± 13 nm and the mean oscillation amplitude was 194 ± 12 nm. Generation of [Ca²⁺] _i waves was also independent of influx of extracellular Ca²⁺. [Ca²⁺] _i waves originated in one cell pole and were visualized as propagation mostly along the subplasmalemmal space or occasionally throughout the cytoplasm. The mean velocity was 23 +3 m per sec (n = 6). Increases of [Ca²⁺] _i induced by different agonists were encoded into changes of baseline [Ca²⁺] _i and the amplitude of oscillations, but not into their frequency. The observed spatiotemporal pattern of [Ca²⁺] _i regulation may be the underlying mechanism for slow wave generation and propagation in this tissue. These findings are consistent with a [Ca²⁺] _i regulation whereby cell regulators modulate the spatiotemporal pattern of intracellularly generated [Ca²⁺] _i oscillations.The authors thank Debbie Anderson for excellent technical assistance with the electron microscopy and Dr. M. Regoli for providing the NK-1 agonist [Sar⁹,Met(O₂)¹¹]-SP. This work was supported by National Institutes of Health Grants DK 40919 and DK 40675 and Veterans Administration Grant SMI.     

Distribution and behaviour of Acetes sibogae Hansen (Decapoda, Crustacea) in an estuary in relation to tidal and diel environmental changes

Quantitative samples of Acetes sibogae were collected at 2 hintervals for 48 h at three sites across the axis of a tidalestuary to examine their distribution within the water bodyover tidal and diel cycles, and to assess the role of behaviourin maintaining population distribution in estuarine/coastalwaters in relation to selected environmental factors. Watertemperature, salinity, tidal height and light intensity wereconcurrently measured. Distribution of the shrimp across theestuary was uniform and consistent between daylight or darkperiods, and among flood or ebb tides. Changes of A.sibogaeabundance were related to light and tidal cycles at each sitewith higher catches in dark periods and during flood tides.Acetes sibogae also exhibited both nocturnal and tidal verticalmovements in the water body, with greater numbers being onlyfound near-surface rather than near-bottom during flood tidesand at night. No significant differences in the distributionof size groups were found between any sampled levels of anysite. Acetes sibogae was highly aggregated in the water body.It is suggested that aggregating behaviour and tidal and nocturnalvertical movements act to facilitate population maintenancein estuarine/coastal waters.