Local and systemic effects of two herbivores with different feeding mechanisms on primary metabolism of cotton leaves

Caterpillars and spider mites are herbivores with different feeding mechanisms. Spider mites feed on the cell content via stylets, while caterpillars, as chewing herbivores, remove larger amounts of photosynthetically active tissue. We investigated local and systemic effects of short-term caterpillar and spider mite herbivory on cotton in terms of primary metabolism and growth processes. After short-term caterpillar feeding, leaf growth and water content were decreased in damaged leaves. The glutamate/glutamine ratio increased and other free amino acids were also affected. In contrast, mild spider mite infestation did not affect leaf growth or amino acid composition, but led to an increase in total nitrogen and sucrose concentrations. Both herbivores induced locally increased dark respiration, suggesting an increased mobilization of storage compounds potentially available for synthesis of defensive substances, but did not affect assimilation and transpiration. Systemically induced leaves were not significantly affected by the treatments performed in this study. The results show that cotton plants do not compensate the loss of photosynthetic tissue with higher photosynthetic efficiency of the remaining tissue. However, early plant responses to different herbivores leave their signature in primary metabolism, affecting leaf growth. Changes in amino acid concentrations, total nitrogen and sucrose content may affect subsequent herbivore performance.     

First isolation of Pseudocohnilembus persalinus (Ciliophora: Scuticociliatida) from freshwater-reared rainbow trout, Oncorhynchus mykiss

Ciliated protists were isolated from the ovarian fluid of apparently healthy adult rainbow trout (Oncorhynchus mykiss) maintained in freshwater. The organism was identified as Pseudocohnilembus persalinus based on morphometric and morphological analysis of silver-stained specimens obtained from culture and on analysis of ribosomal RNA gene sequences. The cytochrome c oxidase subunit 1 gene sequence of this organism also was characterized. This ciliate has been reported previously as free living only in saline environments and as an endosymbiont in a marine teleost, the olive flounder (Paralichthys olivaceus). A cyst-like stage may have facilitated the novel occurrence of this organism as an endosymbiont in rainbow trout.     

添加玉米和水稻秸秆对淹水土壤pH、二氧化碳及交换态铵的影响

通过温室土壤培养试验,研究了不同添加量玉米和水稻秸秆对淹水土壤pH、CO₂及交换态铵的影响.结果表明：在接近中性的土壤中加入秸秆可使土壤pH值降低,4 g·kg^-1玉米和水稻秸秆处理的土壤pH值均与对照差异显著（P＜0.05）,而1 g·kg^-1玉米和水稻秸秆处理与对照差异不显著（P＞0.05）.土壤溶液中的CO₂含量随秸秆添加量的增加而增大,1 g·kg^-1玉米和水稻秸秆处理的土壤溶液CO₂含量最大值分别为35.9％和31.9％（v/v）,与对照（25.8％）差异达显著水平（P＜0.05）,但两者间差异不显著（P＞0.05）;4 g·kg^-1玉米和水稻秸秆处理的土壤溶液CO₂含量最大值分别为54.2％和41.8％（v/v）,与对照差异极显著（P＜0.01）,两者间差异也达显著水平（P＜0.05）.在不施氮肥的情况下,添加秸秆可降低土壤铵态氮浓度,且铵态氮浓度随秸秆添加量的增加而降低,不同添加量处理间差异显著（P＜0.05）;在施入氮肥的情况下,1 g·kg^-1玉米和水稻秸秆处理提高了土壤铵态氮浓度,而4 g·kg^-1玉米和水稻秸秆处理降低了土壤铵态氮浓度.无论是否施入氮肥,玉米和水稻秸秆处理的土壤铵态氮浓度差异不显著（P＞0.05）.     

Identification of Flagellar Motility Genes in Yersinia ruckeri by Transposon Mutagenesis

Here we demonstrate that flagellar secretion is required for production of secreted lipase activity in the fish pathogen Yersinia ruckeri and that neither of these activities is necessary for virulence in rainbow trout. Our results suggest a possible mechanism for the emergence of nonmotile biotype 2 Y. ruckeri through the mutational loss of flagellar secretion.Yersinia ruckeri is the etiologic agent of enteric redmouth disease, a disease of salmonid fish species that is found worldwide in areas where salmonid fish species are farmed (3, 6, 18, 20). Vaccines for enteric redmouth disease have been used successfully for nearly 3 decades and consist of immersion-applied, killed whole-cell preparations of motile serovar 1 Y. ruckeri strains (22). Recently though, outbreaks have been reported in vaccinated fish at trout farms in the United Kingdom (2), Spain (9), and the United States (1). The Y. ruckeri strains isolated from these outbreaks are uniformly atypical serovar 1 isolates lacking both flagellar motility and secreted lipase activity. These variants have been classified as Y. ruckeri biotype 2 (BT2) and are believed to have a reduced sensitivity to immersion vaccination (2). The objective of this study was to obtain a better understanding of the emergence of BT2 Y. ruckeri by identifying genetic elements necessary for expression of the Y. ruckeri flagellum and determining the role that the flagellum plays in virulence by using a rainbow trout infection model.     

An Aeromonas salmonicida type IV pilin is required for virulence in rainbow trout Oncorhynchus mykiss

Aeromonas salmonicida expresses a large number of proven and suspected virulence factors including bacterial surface proteins, extracellular degradative enzymes, and toxins. We report the isolation and characterization of a 4-gene cluster, tapABCD, from virulent A. salmonicida A450 that encodes proteins homologous to components required for type IV pilus biogenesis. One gene, tapA, encodes a protein with high homology to type IV pilus subunit proteins from many gram-negative bacterial pathogens, including Aeromonas hydrophila, Pseudomonas aeruginosa, and Vibrio vulnificus. A survey of A. salmonicida isolates from a variety of sources shows that the tapA gene is as ubiquitous in this species as it is in other members of the Aeromonads. Immunoblotting experiments demonstrate that it is expressed in vitro and is antigenically conserved among the A. salmonicida strains tested. A mutant A. salmonicida strain defective in expression of TapA was constructed by allelic exchange and found to be slightly less pathogenic for juvenile Oncorhynchus mykiss (rainbow trout) than wild type when delivered by intraperitoneal injection. In addition, fish initially challenged with a high dose of wild type were slightly more resistant to rechallenge with wild type than those initially challenged with the tapA mutant strain, suggesting that presence of TapA contributes to immunity. Two of the other three genes identified, tapB and tapC, encode proteins with homology to factors known to be required for type IV pilus assembly in P. aeruginosa, but in an as yet unidentified manner. TapB is a member of the ABC-transporter family of proteins that contain characteristic nucleotide-binding regions, and which may provide energy for type IV pilus assembly through the hydrolysis of ATP. TapC homologs are integral cytoplasmic membrane proteins that may play a role in pilus anchoring or initiation of assembly. The fourth gene, tapD, encodes a product that shares homology with a family of proteins with a known biochemical function, namely, the type IV prepilin leader peptidases. These bifunctional enzymes proteolytically cleave the leader peptide from the pilin precursor (prepilin) and then N-methylate the newly exposed N-terminal amino acid prior to assembly of the subunits into the pilus structure. We demonstrate that A. salmonicida TapD is able to restore type IV pilus assembly and type II secretion in a P. aeruginosa strain carrying a mutation in its type IV peptidase gene, suggesting that it plays the same role in A. salmonicida.     

Combined prime-boost vaccination against tick-borne encephalitis (TBE) using a recombinant vaccinia virus and a bacterial plasmid both expressing TBE virus non-structural NS1 protein

Background  

Heterologous prime-boost immunization protocols using different gene expression systems have proven to be successful tools in protecting against various diseases in experimental animal models. The main reason for using this approach is to exploit the ability of expression cassettes to prime or boost the immune system in different ways during vaccination procedures. The purpose of the project was to study the ability of recombinant vaccinia virus (VV) and bacterial plasmid, both carrying the NS1 gene from tick-borne encephalitis (TBE) virus under the control of different promoters, to protect mice against lethal challenge using a heterologous prime-boost vaccination protocol.     

Characterization and molecular genetic complementation of mutants affecting dimorphism in the fungus ustilago maydis

Ustilago maydis, the causal agent of corn smut disease, displays dimorphic growth in which it alternates between a unicellular, nonpathogenic yeast-like form and a dikaryotic, pathogenic filamentous form. Previously, a constitutively filamentous haploid mutant was obtained. Complementation of this mutant led to the isolation of the gene encoding adenylate cyclase, uac1. Secondary mutagenesis of a uac1 disruption strain allowed the isolation of a large number of suppressor mutants, termed ubc, for Ustilago bypass of cyclase, lacking the filamentous phenotype. Analysis of one of these suppressor mutants previously led to the identification of the ubc1 gene, encoding the regulatory subunit of cAMP-dependent protein kinase. In this report we describe the isolation of cosmids containing three new ubc genes, termed ubc2, ubc3, and ubc4. We also describe the morphology of the ubc2, ubc3, and ubc4 mutants in a uac1- background as well as in a background with a functional uac1 gene. In addition, we describe several mutant strains not complemented with any of the genes currently in hand and that are thus presumed to possess mutations in additional ubc genes. Copyright 1998 Academic Press.     

Body size effects and rates of cytochrome b evolution in tube-nosed seabirds

Variation in rates of molecular evolution now appears to be widespread. The demonstration that body size is correlated with rates of molecular evolution suggests that physiological and ecological factors may be involved in molecular rate variation, but large-scale comparative studies are still lacking. Here, we use complete cytochrome b sequences from 85 species of tube-nosed seabirds (order Procellariiformes) and 5 outgroup species of penguins (order Sphenisciformes) to test for an association between body mass and rates of molecular evolution within the former avian order. Cladistic analysis of the 90 sequences estimates a phylogeny largely consistent with the traditional taxonomy of the Procellariiformes. The Diomedeidae, Procellariidae, and Pelecanoididae are monophyletic, while the Hydrobatidae are basal and paraphyletic. However, the two subfamilies within the Hydrobatidae (Hydrobatinae and Oceanitinae) are monophyletic. A likelihood ratio test detects significant deviation from clocklike evolution in our data. Using a sign test for an association between body mass and branch length in the seabird phylogeny, we find that larger taxa tend to have shorter terminal branch lengths than smaller taxa. This observation suggests that rates of mitochondrial DNA evolution are slower for larger taxa. Rate calibrations based on the fossil record reveal concordant body size effects. We interpret these results as evidence for a metabolic rate effect, as the species in this order exhibit large differences in metabolic rates, which are known to be highly correlated with body mass in this group. Our results support previous findings of body size effects and show that this effect can be significant even within a single avian order. This suggests that even lineage-specific molecular clocks may not be tenable if calibrations involve taxa with different metabolic rates.