Zooplankton decline in the Černé Lake (Šumava Mountains,Bohemia) as reflected in the stratification of cladoceran remains in the sediment

Stratigraphy of cladoceran remains in the upper 18 cm of a sediment core from the Lake Černé was studied. The successive disappearance of Bosmina longispina, Daphnia longispina and Ceriodaphnia quadrangula from the upper layers of the sediment corresponds with our knowledge concerning the disappearance of these species from the open water.     

Protein synthesis in tobacco pollen tubes: preferential synthesis of cell-wall 69-kDa and 66-kDa glycoproteins

One- and two-dimensional electrophoresis of Nicotiana tabacum pollen and pollen tube proteins confirmed that a new protein is preferentially synthesized during pollen germination and tube growth and becomes the most abundant protein in pollen tubes. Analysis of proteins extracted with sodium dodecyl sulfate (SDS) from different pollen tube fractions showed that it is the most abundant non-covalently bound wall protein, characterized by molecular mass of 69 kDa, pI between 7.9 and 8.2, and glycosylation with glucose and/or mannose. Amino acid analysis revealed relative abundance of serine, glutamic acid and glycine, but did not show the presence of hydroxyproline. According to all these characteristics, it cannot be classified as an extensin-like protein. Another prominent wall-bound glycoprotein has a molecular mass of 66 kDa and the same pI as the 69 kDa glycoprotein. These two glycoproteins are similar also in ConA binding, rate of synthesis, and rapid incorporation into pollen tube walls. Their synthesis is strongly reduced by tunicamycin and this inhibition results in the occurrence of new polypeptides in the range of 57–61 kDa. Tunicamycin also inhibited pollen tube growth. At 10 ng ml^-1 and 50 ng ml^-1 the inhibitor reduced pollen tube mass after 24 h of culture by 30% and 85%, respectively. This indicates that tobacco pollen presents a system highly sensitive to tunicamycin and that cotranslational N-linked glycosylation on the rough endoplasmic reticulum is required for 66 and 69 kDa glycoprotein formation and for pollen tube growth. Although other proteins appear during pollen germination and tube growth, the new proteins occur at low levels and seem to originate through modifications of preexisting polypeptides. In contrast to 69 and 66 kDa proteins, most proteins detected by [¹⁴C]amino acid incorporation and fluorography of gels were not revealed by Coomassie blue staining.     

细叶黄芪叶肉原生质体发育早期细胞壁再生的研究

采用透射电镜术、电镜多糖细胞化学染色、细胞壁荧光染色以及香豆素抑制细胞壁再生等方法,对细叶黄芪（Ａｓｔｒａｇａｌｕｓｍ ｅｌｉｌｏｔｏｉｄｅｓ ｖａｒ．ｔｅｎｕｉｓ）叶肉原生质体细胞壁的再生及其化学特点进行了研究。结果表明,离体培养２４ 小时的原生质体表面产生一些突起小泡,有时可见少量纤维组分的形成。培养３ 天时这种纤维组分明显增多。至５ 天时可清楚看到再生壁是由纤维和颗粒构成。六亚甲四胺银染色证明它们都是由多糖组分组成的。另外,培养３６ 小时的原生质体有相互粘连的现象。电镜观察、荧光染色及香豆素处理的研究表明粘连与再生壁的形成有关。根据上述观察结果,对原生质体再生壁的结构及其化学性质等问题进行了讨论     

Zn对细胞保护作用机理的研究

应用扫描质子微探针和同步辐射ｘ荧光分析技术测定了细胞中元素的分布和组成,为确定Zn是细胞结构成分提供了直接的实验依据.用上述核技术结合有关生化指标,分析测定了正常和损伤细胞（脂质过氧化损伤）中Fe,Zn和丙二醛、SH基含量变化的相互关系.实验结果表明,当细胞发生脂质过氧化损伤时,Fe含量和丙二醛含量同步增高,而Zn含量和SH基量则降低.给细胞补充Zn后,提高了细胞质膜中的Zn含量,SH基量也随之增加,同时丙二醛量降低.提示Zn保护细胞完整性的作用机理之一是控制脂质过氧化作用.Zn可保护膜蛋白的SH基,减少和阻止被Fe所催化的过氧化反应.     

Reversible and irreversible modifications ofβ-lactoglobulin upon exposure to heat

Modifications in the exposure to the solvent of hydrophobic residues, changes in their organization into surface hydrophobic patches, and alterations in the dimerization equilibrium ofβ-lactoglobulin upon thermal treatment at neutralpH were studied. Exposure of tryptophan residues was temperature dependent and was essentially completed on the time scale of seconds. Reorganization of generic hydrophobic protein patches on the protein surface was monitored through binding of 1,8-anilinonaphthalenesulfonate, and was much slower than changes in tryptophan exposure. Different phases in surface hydrophobicity changes were related to the swelling and the subsequent collapse of the protein, which formed a metastable swollen intermediate. Heat treatment ofβ-lactoglobulin also resulted in the formation of soluble oligomeric aggregates. The aggregation process was studied as a function of temperature, demonstrating that (i) dimer dissociation was a necessary step in a sequential polymerization mechanism and (ii) cohesion of hydrophobic patches was the major driving force for aggregation.     

细叶黄芪叶肉原生质体发育早期几种细胞器的变化

在细叶黄芪叶肉原生质体发育早期,细胞器的变化较大。离体培养4h后,线粒体的嵴和基质物质开始增加。培养3—5天后,线粒体的数量增加5倍以上,此时可见大部分线粒体围绕细胞核分布。在培养24h后,高尔基体开始发育,它们主要分布在细胞质周边区域。多糖细胞化学染色表明,高尔基体内沉积着大量嗜银物质。培养1天后,粗面内质网开始发育。培养3天时,部分叶绿体边缘出现一些空隙结构。随着叶绿体内膜结构的消失,淀粉粒增大,叶绿体逐渐转变为造粉质体。     

Bacterioplankton interactions with Daphnia and algae in experimental enclosures

Development of bacterioplankton was studied by manipulation of planktivorous fish and/or nutrients in experimental enclosures in a fish pond. Grazing pressure exerted by large zooplankton (Daphnia galeata and Daphnia pulicaria) strongly influenced the counts and size distribution of bacterial populations. Morphometric analyses by scanning electron microscope revealed a shift in size distribution from larger mainly rod-type bacteria under low grazing pressure towards smaller mainly coccus-type under strong grazing pressure. The metabolic activity of bacteria measured as glucose uptake was higher under strong grazing pressure. After removal of large daphnids, the increase in bacterial density was probably the result of two additive factors: low grazing pressure and high level of dissolved organic matter (DOM) due to photosynthetic activity of more abundant algae. Composition of bacterial populations shifted toward larger, rod-type bacteria, and their metabolic efficiency measured by uptake, was lowered. The basic dimensionality of the system and interactions between variables was describe by R-mode factor analysis. The manipulated enclosures were relate with factor score.     

Characterization of the traC determinant of the Enterococcus faecalis hemolysin-bacteriocin plasmid pAD1: binding of sex pheromone.

pAD1, a conjugative, 60-kb, hemolysin-bacteriocin plasmid in Enterococcus faecalis, encodes a mating response to a small peptide sex pheromone, cAD1, secreted by potential recipient bacteria. A gene, traC, encoding a 60.7-kDa protein with a typical amino terminal signal peptide, was identified within a region that appears to encode a product that binds to exogenous pheromone. A cloned segment of DNA containing traC resulted in specific binding of cells to synthetic cAD1. The putative traC product has strong similarity to a product of the E. faecalis plasmid pCF10 as well as oligopeptide binding proteins of Escherichia coli, Salmonella typhimurium, and Bacillus subtilis.     

Relationships among non-Acremonium sp. fungal endophytes in five grass species.

Many cool-season grasses (subfamily Pooideae) possess maternally transmitted fungal symbionts which cause no known pathology and often enhance the ecological fitness and biochemical capabilities of the grass hosts. The most commonly described endophytes are the Acremonium section Albo-lanosa spp. (Acremonium endophytes), which are conidial anamorphs (strictly asexual forms) of Epichloë typhina. Other endophytes which have been noted are a Gliocladium-like fungus in perennial ryegrass (Lolium perenne L.) and a Phialophora-like fungus in tall fescue (Festuca arundinacea Schreb.). Here, we report the identification of additional non-Acremonium sp. endophytes (herein designated p-endophytes) in three more grass species: Festuca gigantea, Festuca arizonica, and Festuca pratensis. In each grass species, the p-endophyte was cosymbiotic with an Acremonium endophyte. Serological analysis and sequence determinations of variable portions of their rRNA genes indicated that the two previously identified non-Acremonium endophytes are closely related to each other and to the newly identified p-endophytes. Therefore, the p-endophytes represent a second group of widely distributed grass symbionts.