Turbidometric Measurement of a Protozoan-produced Growth-promoting Factor

Process diagrams are important tools in biology for explaining processes such as protein synthesis, compound cycles and the like. The aim of the present study was to measure the ability to solve process-diagram problems in biology and its relationship with prior knowledge, spatial ability and working memory. For this purpose, we developed a test that represents process diagrams and adjacent tasks used in secondary education biology. Results show that the ability to solve process-diagram problems is correlated to prior knowledge, spatial abilities and visuospatial working memory capacity. A difference in impact of spatial skills was demonstrated for the level of cognitive demand when solving process-diagram problems.     

The pleiotypic response in mammalian cells: search for an intracellular mediator

The reactions included in the definition of this regulatory program, called the “pleiotypic response”, are very similar to those under “stringent” control in bacteria. The latter appears to be mediated by a novel nucleotide, ppGpp, and we therefore assayed for the presence of this nucleotide in cultured fibroblasts under a variety of conditions of growth restriction which elicit the pleiotypic response. We were unable to detect it in any of these circumstances and we conclude that ppGpp is not the mediator of the pleiotypic response, at least in the cell lines studied.     

The pleiotypic response to serine in erythroblastic leukemic cells

Erythroblastic leukemic (EBL) cells incubated in media containing essential amino acids, glutamine and serine incorporate more [3H]-leucine into protein than those incubated without serine. Cells incubated with serine contain higher intracellular serine concentrations and display increased rates of peptide chain initiation on polyribosomal profile analysis. Deficiency of serine inhibited protein synthesis more than deficiencies of most other single essential amino acids, but no further inhibition was seen when single essential amino acids were removed from serine deficient media. Serine also enhanced the uptake of [3H]-uridine and its transfer to RNA while several essential amino acids had no effect. We conclude that in EBL cells, serine is an essential amino acid and that exogenous repletion of intracellular concentrations induces a positive pleiotypic response. We have previously shown that after incubation with serine for 15 min. EBL cells have greater numbers of plasmalemma insulin receptors. Regulation of cell surface receptors may therefore comprise another limb of the pleiotypic response.     

辣椒根际促生菌的分离筛选及抗病促生特性研究

获得辣椒根际促生菌(Plant growth promoting rhizobacteria,PGPR)并探究其抗病促生特性。采用固氮、无机磷和有机磷培养基从江苏省徐州市采集的辣椒根际土壤中分离筛选根际促生菌株(PGPR),通过形态特征及16S rDNA序列分析进行菌株鉴定,对菌株的固氮、解磷、分泌3-吲哚乙酸(IAA)能力及对4种辣椒病害病原菌抗病能力进行探究。得到13株辣椒PGPR菌株,经鉴定分别属于Bacillus、Pseudomonas、Lelliottia、Siccibacter、Achromobacter、Microbacterium和Paenibacillus;13株PGPR菌株均有固氮功能;其中7株可解有机磷,分别属于Lelliottia、Bacillus、Siccibacter、Microbacterium、Paenibacillus;5株可解无机磷,分别属于Lelliottia、Bacillus、Siccibacter、Pseudomonas;3株具有分泌IAA能力,分别属于Lelliottia、Siccibacter、Bacillus;5株具有抗病能力,分别属于B...     

Growth-promoting effects of a bacterium on raphidophytes and other phytoplankton

On 29 April 2003, a Heterosigma akashiwo bloom (9.5 × 10⁴ cells mL⁻¹) associated with a fish kill (>10⁴ dead fishes estimated from aerial surveys) was observed offshore of Bulls Bay, McLellanville, South Carolina, USA. To assess a potential cause of this bloom event, we investigated the bacterial diversity and algal/bacterial interactions in the bloom microbial community. Thirty-five bacterial strains were isolated and screened for algicidal or algal growth-promoting activities. One strain (BBB25) had significant growth-promoting effects on all 7 algal species tested: three raphidophytes (Heterosigma akashiwo, Chattonella subsalsa, Fibrocapsa japonica), two diatoms (Chaetoceros neogracile, Nitzschia sp.), a cryptophyte (Cryptomonas sp.), and a chlorophyte, Ankistrodesmus sp. This strain (BBB25) is a Gram-positive, rod-shaped spore-forming bacterium. Partial 16S rDNA gene sequence and morphological characters indicated that BBB25 is related closely to the genus Bacillus. The general nature of the algal response indicates that the growth-promoting effects of BBB25 are not specific to H. akashiwo, and suggests potentially widespread effects. Since the presence or relative abundance of the other algal species was not assessed during the bloom initiation period, the selective stimulatory effect on H. akashiwo bloom formation in Bulls Bay is unknown. These results demonstrate, however, the potential for bacterial species to play a regulatory role in bloom formation.     

Dissociation, aggregation of sesame alpha-globulin in nonionic detergent solution.

Nonionic detergents Triton X-100 and Brij 36T induce dissociation and aggregation of the protein sesame alpha-globulin above the critical micelle concentrations (cmc) of the detergents. Spectrophotometric titration in Triton shows no change in the pKInt value of the tyrosyl groups at 1x10-3 M detergent where both dissociation and aggregation of the protein are observed. Fluorescence measurement does not indicate any change in the environment of the tryptophan groups of the protein in Brij. Viscosity measurements show no major conformational change of the protein in the detergent solution. Binding measurements suggest that perhaps micelles of the detergent predominantly bind to the protein. The detergent micelles preferentially bind to the exposed hydrophobic surfaces of the protein subunits. The association of the protein detergent complex through electrostatic interaction is probably responsible for the formation of the aggregates.     

Tissue plasminogen activator is a potent activator of PDGF-CC

Tissue plasminogen activator (tPA) is a serine protease involved in the degradation of blood clots through the activation of plasminogen to plasmin. Here we report on the identification of tPA as a specific protease able to activate platelet-derived growth factor C (PDGF-C). The newly identified PDGF-C is secreted as a latent dimeric factor (PDGF-CC) that upon proteolytic removal of the N-terminal CUB domains becomes a PDGF receptor alpha agonist. The CUB domains in PDGF-CC directly interact with tPA, and fibroblasts from tPA-deficient mice fail to activate latent PDGF-CC. We further demonstrate that growth of primary fibroblasts in culture is dependent on a tPA-mediated cleavage of latent PDGF-CC, generating a growth stimulatory loop. Immunohistochemical analysis showed similar expression patterns of PDGF-C and tPA in developing mouse embryos and in tumors, indicating both autocrine and paracrine modes of activation of PDGF receptor-mediated signaling pathways. The identification of tPA as an activator of PDGF signaling establishes a novel role for the protease in normal and pathological tissue growth and maintenance, distinct from its well-known role in plasminogen activation and fibrinolysis.     

Growth-promoting effect of carbon material upon bacterial cells propagating through a distance

Carbon material such as graphite and activated charcoal, but not diamond, causes the promotion of growth of certain bacteria under ordinarily non-permissive stress conditions over a distance of several centimeters. Bacillus carboniphilus under the stress of a high KCl concentration and high temperature responded to this remote effect of carbon material with enhanced growth, and thermophile bacterium Bacillus stearothermophilus responded similarly yet moderately under the stress of low temperature. The remote effect of carbon was caused by its activation with external energy, probably of electromagnetic nature, as this effect was markedly decreased by sheltering the experimental system with an iron or aluminum barrier. Carbon material probably transforms the external oscillatory pulses or radiation into a signal exerting, far-reaching, growth-promoting effect upon cells. The most plausible candidate of signals emitted from carbon was considered to be (ultra)sonic.     

Growth-promoting factors for yeast cells ofParacoccidioides brasiliensis

Low-density seedings of yeast cells ofParacoccidioides brasiliensis give poor growth (as assessed by plating efficiency test) on conventional mycological agar media, and therefore growth-promoting factors for this fungus were sought. Water-extracts of yeast cells of sixP. brasiliensis isolates were all considerably effective in promoting the growth of low-density seedings ofP. brasiliensis isolates Pb-18 and Hachisuga, but had little effect on isolate Bt-4. Horse serum, at a concentration range of 2–4%, moderately or considerably promoted the growth of theseP. brasiliensis isolates. Combinations of the fungus cell extracts with horse serum were highly effective in promoting the growth of all of the fungal isolates. The fungus cell extracts showed siderophore (microbial iron carrier) activity. An iron-chelator, ethylenediaminetetraacetic acid, at a concentration of 100 μM also highly promoted the growth of the fungal isolates in the presence of horse serum, and ferric ion added to culture medium was considerably effective in the growth promotion. These results suggest that deficient utilization of external iron by the fungus cell is one of the growth-limiting processes for low-density seedings of yeast cells ofP. brasiliensis on conventional mycological agar media.     

Growth-promoting activity of some selectively modified gibberellins

Synthetic gibberellin analogues derived mainly from GA₃ were tested for their growth-promoting activity in three standard bioassay systems (dwarf pea, cucumber and lettuce). The highest potency in all the tests was displayed by 13-O-methyl-GA₃, while in the case of 7-homo-GA₃ a large decrease in activity was observed. No obvious correlation could be found between the partitioning of acidic analogues between ethyl acetate and water and their biological potencies. The results of the bioassays appear to be compatible with the assumption that it is the spatial correspondence between an active gibberellin (such as GA₃ or GA₇) and a specific receptor that plays the prime role in the growth response.     

内生菌与植物的相互作用：促生与生物薄膜的形成

植物内生菌由于其独特的生态学地位而广受关注,近年来有关植物内生菌与宿主相互作用的研究取得了很大进展.本文综述了植物内生菌通过分泌促生物质、拮抗病原菌等实现与宿主共生互作,同时植物为内生菌提供适宜的黏附表面,使其形成以生物薄膜(biofilm)为主要形式的多细胞聚集体结构以更好地适应周围的生存环境,从而更加高效地对植物产生促生作用.本文论述了内生菌在与植物的互作中形成的多细胞聚集结构在抵抗非生物胁迫方面的独特生理及生态学意义,结合水稻内生成团泛菌YS19形成多细胞聚集体symplasmata现象及其生物学效应,对未来有关植物内生菌的研究方向提出了一些看法.