DcrA, a c-type heme-containing methyl-accepting protein from Desulfovibrio vulgaris Hildenborough, senses the oxygen concentration or redox potential of the environment.

The amino acid sequence of DcrA from Desulfovibrio vulgaris Hildenborough, a strictly anaerobic, sulfate-reducing bacterium, indicated homology with the methyl-accepting chemotaxis proteins from enteric bacteria (A. Dolla, R. Fu, M. J. Brumlik, and G. Voordouw, J. Bacteriol. 174:1726-1733, 1992). The homology is restricted to the cytoplasmic C-terminal signaling domain. The periplasmic N-terminal sensor domain was found to contain a unique sequence, CHHCH, corresponding to a consensus c-type heme binding site. A pretreated, DcrA-specific polyclonal antiserum, generated against DcrA protein overproduced in Escherichia coli, was used for immunoprecipitation of 35S-labeled DcrA from D. vulgaris and Desulfovibrio desulfuricans G200(pJRFR2), a transconjugant that overexpresses functional DcrA. Labeling of the latter with the heme precursor 5-amino-[4-14C]levulinic acid, followed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and fluorography, confirmed the presence of c-type heme, while labeling with L-[methyl-3H]methionine in the absence of protein synthesis confirmed that DcrA is a methyl-accepting protein. The base liability of the incorporated radioactivity indicated methyl ester formation like that occurring in the methyl-accepting chemotaxis proteins of enteric bacteria. L-[methyl-3H]methionine labeling of D. desulfuricans G200(pJRFR2) under different conditions indicated that methyl labeling of DcrA decreased upon addition of oxygen and increased upon subsequent addition of the reducing agent dithionite. These results indicate that DcrA may serve as a sensor of oxygen concentration and/or redox potential.     

Amphetamine Promotes Neostriatal Ascorbate Release via a Nigro-Thalamo-Cortico-Neostriatal Loop

Abstract: In the neostriatum, amphetamine and other dopamine agonists elevate the extracellular level of ascorbate, which is known to modulate neostriatal function. Although both D₁ and D₂ receptors have been linked to neostriatal ascorbate release, ample evidence suggests it is controlled by areas outside the neostriatum. The present series of experiments used selective lesions and intracerebral drug infusions to probe the involvement of the ventromedial thalamus and substantia nigra pars reticulata. Our results implicate both of these sites in amphetamine-induced increases in the release of neostriatal ascorbate. Thus, whereas unilateral electrolytic lesions of the substantia nigra pars reticulata completely abolished the ability of systemic amphetamine (2.5 mg/kg) to increase extracellular ascorbate in ipsilateral neostriatum, intranigral infusions of this drug (10 and 30 µg/µl) elevated neostriatal ascorbate release. This infusion effect, moreover, was blocked by electrolytic lesions of the ipsilateral ventromedial thalamus, which receives input from the substantia nigra pars reticulata and projects to the cerebral cortex. These results, combined with previous evidence implicating cortical projections to neostriatum as the source of extracellular ascorbate, suggest that neostriatal ascorbate release is regulated, at least in part, by a nigro-thalamo-cortico-neostriatal pathway.     

Map locations of mouse hepatitis virus temperature-sensitive mutants: confirmation of variable rates of recombination.

Using standard genetic recombination techniques, studies in our laboratory suggest that recombination rates are very high and vary in different portions of the mouse hepatitis virus (MHV) genome. To determine the actual recombination frequencies in the MHV genome and localize the nucleotide boundaries of individual viral genes, we have sequenced temperature-sensitive and revertant viruses to identify the location of specific mutant alleles. Complementation group F RNA+ ts mutants (LA7, NC6, and NC16) each contained a unique mutation which was tightly linked to the ts phenotype and resulted in a conservative or nonconservative amino acid change in the MHV S glycoprotein gene. In agreement with previous recombination mapping studies, the mutation in LA7 and NC6 mapped within the S1 domain while NC16 mapped within the S2 domain. To determine the map coordinates of the MHV polymerase genes, several RNA- mutants and their revertants belonging to complementation groups C (NC3 and LA9) and E (LA18 and NC4) were also sequenced. Mutations were identified in each virus that were tightly linked to the ts phenotype and resulted in either a conservative or nonconservative amino acid change. The group C allele spanned the ORF 1a/ORF 1b junction, while the group E mutants mapped at the C terminus of ORF 1b about 20 to 22 kb from the 5' end of the genome. Mutation rates, calculated from the reversion frequencies of plaque-purified ts viruses requiring a single nucleotide alteration for reversion, approached 1.32 (+/- 0.89) x 10(-4) substitutions per nucleotide site per round of template copying. Detailed recombination mapping studies across known distances between these different ts alleles has confirmed that homologous recombination rates approached 25% and varied within different portions of the MHV genome.     

银杏授粉研究初报

本文报道银杏授粉的适宜品种,气候条件、不同时期、方法、浓度、雌花不同发育阶段等试验结果．为提高银杏的座果率提供有效的技术措施。     

银杏扦插繁殖试验

本文报道银杏扦插繁殖技术。采用不同插穗、机械处理、不同激素及浓度处理进行扦插繁殖试验．扦插成活率可达９０—１００％。     

边界层阻力在叶片气体交换过程中的作用

作者对现有的气体交换法的叶室作了改进。从实验上检验了作者根据电学类比分析和模拟检验得到的结论：在已有的气体交换测定装置中,空气流速不变,叶片的边界层导度也固定不变,所得到的结论用于边界层导度变化的情形时,会造成比较大的误差。现加一障碍物使得流过叶片的风速减小,从而改变叶片的边界层导度。通过测量在不同边界层导度下同一叶片的光强曲线可以考察不同边界层导度下的气孔导度、光合速率、蒸腾速率以及它们之间的相互关系。实验结果与作者以前的电学类比分析和模拟得到的结论是基本一致的     

沈阳西部污灌水中有机污染物的分析

沈阳西部污灌水中有机污染物的分析刘海玲,张丽珊,姚家彪,于殿臣,朱岩,可夫,姜萍（中国科学院沈阳应用生态研究所,１１００１５）ＡｎａｌｙｓｉｓｏｆＯｒｇａｎｉｃＰｏｌｌｕｔａｎｔｓｉｎＩｒｒｉｇａｔｅｄｓｅｗａｇｅＩｎＷｅｓｔｅｒｎＳｈｅｎｙａｎｇ．...     

Effects of omnivorous shrimp in a montane tropical stream: sediment removal,disturbance of sessile invertebrates and enhancement of understory algal biomass

Freshwater shrimp dominate the faunal biomass of many headwater tropical streams: however, their role in community organization is unclear. Enclosure/exclosure experiments in a montane Puerto Rican stream examined direct and indirect effects of two dominant taxa of atyid (Atyidae) shrimp, Atya lanipes Holthuis and Xiphocaris elongata Guerin-Meneville. Both shrimp taxa caused significant reductions in sediment cover on rock substrata, reducing sedimentation and enhancing algal biovolume on clay tiles in cages. When tiles incubated in shrimp exclosures for 2 wks were placed outside of cages, atyid shrimp removed 100% of the sediment cover within a 30 min observation period. Atyid shrimp appear to play an important role in stream recovery after high discharge events by rapidly removing sediments and detritus deposited on benthic substrata in pools. We evaluated the mechanism by which A. lanipes influences algae and benthic insects by comparing patterns of algal biomass, taxonomic composition, and insect abundance between shrimp-exclusion and shrimp-presence treatments both with and without manual sediment removal. The shrimp exclusion treatment without manual sediment removal bad significantly lower algal biomass and greater sedimentation than all other treatments. The treatment in which shrimp were excluded but sediment was manually removed, however, accrued almost the same algal biovolume as the shrimp enclosure treatment, supporting the hypothesis that sediment removal enhances the biovolume of understory algal taxa. Algal community composition was similar between stream bottom bedrock exposed to natural densities of shrimp and all experimental treatments for both Atya and Xiphocaris: a diatom community strongly dominated (78–95%) by the adnate taxon, Achnanthes lanceolata Breb ex. Kutz. Atyid shrimp are important in determining the distribution and abundance of benthic insects through both direct and indirect effects. Sessile, retreat-building chironomid larvae (Chironomidae: Diptera) are negatively affected by both A. lanipes and X. elongata, through direct removal by foraging activities and/or indirectly through depression of sediment resources available to larvae for the construction of retreats. In constrast, the mobile grazer, Cloeodes maculipes (Baetidae: Ephemeroptera) was not adversely affected and atyid shrimp have the potential to exert positive indirect effects on this taxon by facilitating its exploitation of algal resources and/or through enhancement of understory algal food resources through sediment removal.     

Bacterial heterogeneity in deep subsurface tunnels at Rainier Mesa,Nevada test site

To characterize the deep subsurface environment of Rainier Mesa, Nevada Test Site, rock samples were taken from tunnels U 12b, U12g, U12p, and U 12n, which varied in depth from 50 m to 450 m and in gravimetric moisture content from 4% to 27%. Values for total count, viable count, biomass, Simpson diversity, equitability, similarity coefficient, and number of distinct colony types indicated microbiological variability between samples. Viable counts ranged from less than 1 × 10¹ to 2.4 × 10⁵ CFU g dry wt^–1 of rock. Direct counts and enumeration based on phospholipid determination indicated larger numbers of cells g dry wt-1 of rock than viable counts. Simpson diversity indices, equitability, and numbers of distinct colony types varied from 3.00 to 8.05, 0.21 to 0.89, and 7 to 19, respectively, and indicated heterogeneity between samples. Each distinct morphotype was purified and characterized. Gram reaction, morphology, metal and antibiotic resistances, and metabolic activities of each isolate confirmed spatial variability among microbiota isolated from different locations. Most probable numbers of nitrifying, sulfur oxidizing, and sulfur-reducing bacteria were below the limit of detection in all samples, while the numbers of nitrogen fixing bacteria ranged from below the level of detection to 7.8 × 10² cells g dry wt^–1 of rock sample, and the numbers of dentrifying bacteria ranged from below the level of detection to greater than 1.6 × 10³ cells g dry wt^–1 of rock sample. Offprint requests to: P. S. Amy.