Defoliation and below-ground herbivory in the grass Muhlenbergiaquadridentata : Effects on plant performance and on the root-feeder Phyllophaga sp. (Coleoptera, Melolonthidae)

In this study we evaluated (1) the combined effects of simulated defoliation and below-ground herbivory (BGH) on the biomass and nitrogen content of tillers and roots of the bunchgrass Muhlenbergia quadridentata and (2) the effect of defoliation on the survival of third-instar root-feeder larvae of Phyllophaga sp. The experiment was performed in a pine forest area at an altitude of 3200 m above sea level. The grass and the root-feeder species were native and dominant in the understory and in the macroarthropod root-feeder communities, respectively. Plants were established in pots in the field and were subjected to the following treatments in a factorial design: simulated defoliation (three levels) and BGH (with or without root-feeder larvae) with ten replicates per treatment. Plants were defoliated three times at 2-month intervals. The interaction between defoliation and root herbivory was significant for all components of plant biomass. In every case, light defoliation with BGH decreased live above-ground, root and total plant biomass, and the number of live tillers by more than 50% with respect to the same defoliation level without root-feeders. Plants apparently did not compensate for the carbon drain by root-feeders when a high proportion of older leaves were not removed by defoliation. Plants under heavy defoliation were not affected by the presence of root-feeders and showed a greater live/dead above-ground biomass ratio than lightly defoliated and control plants. Defoliation and BGH did not change tiller and root N concentrations but root herbivores did decrease live-tiller N content in lightly defoliated plants. Root-feeders but not defoliation decreased the root/shoot ratio by 40% and the live/dead above-ground biomass ratio by 45% through increased tiller mortality. Survivorship and final biomass of Phyllophaga sp. larvae were not affected by defoliation treatments during the 6-month study period. Received: 17 May 1996 / Accepted: 1 November 1996     

Metabolic activity of phagocytes in experimental sporotrichosis

Phagocytosis plays an important role as a protective mechanism against infections, since polymorphonuclear leukocytes (PMN) and macrophages are the first cellular lines opposed to agressive microorganisms. In patients with sporotrichosis a diminished capability of killing engulfed yeast by their PMN has been described, but the origin of this deficiency remains unknown.In this work, partial aspects of the oxidative metabolism of PMN leukocytes and peritoneal macrophages of mongolian gerbils experimentally infected with sporotrichosis were studied. For this purpose the nitroblue tetrazolium (NBT) test as described by Baehner and Nathan (1) and myeloperoxidase activity measured according to Kaplow's method were utilized.The PMN and macrophages of mongolian gerbils infected with sporotrichosis showed increased reduction of NBT when compared with the phagocytic cells of normal ones, as is usually observed in most infections. Myeloperoxidase activity was diminished in both PMN and macrophages, but this diminution was statistically significant only in PMN leukocytes. These results show that part of the oxidative mechanisms of phagocytic cells can be impaired in experimental sporotrichosis, and could be correlated with the diminished fungicidal activity of PMN leukocytes obtained from patients infected with sporotrichosis.     

Interactions among phospholipids of guinea pig rough microsomes,effect of fat deficiency

Summary The fatty acid composition and the steady-state fluorescence anisotropy (r_s) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were determined for each of the five major phospholipid (PL) classes present in the liver rough microsomes (RM) of guinea pigs fed with control and fat-deprived diets. In order to obtain information about PL-PL interactions and their contribution to the overall membrane fluidity the experimental r_s of phospholipid mixtures were compared to the molar weighed average values of the individual phospholipid r_s values. The PL ratios in the mixtures were the same to those found in the RM membranes. Binary mixtures of phosphatidylcholine (PC) with phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI) and sphingomyelin (SM) show higher values of r_s than those estimated from the individual component parameters indicating a rigidizing interaction. The rigidizing effect of PE was also observed when this phospholipid was sonicated with mixtures of PC with PS and PI. However, no rigidizing effect of PE was observed in the PC bilayers when SM was included in the composition suggesting that PE-SM interactions prevent rigidizing effects of PE. Besides, in spite that PC-PI and PC-PS mixtures have rigidizing interactions, the incorporation of PI and PS to PC-PS and PC-PI mixtures, respectively, have a fluidizing effect. In consequence, phospholipid polar head groups interact in RM membranes modifying the molecular packing and/or the rotational diffusion of acyl chains. The complexity and variety of constituent phospholipids could prevent major changes in the fluidity. The comparison of results obtained with PL mixtures of control and fat-deficient animals indicate that a change in the number of double bonds does not evoke a significant difference between either the rigidizing of fluidizing effects. However, there is a general tendency indicating that phospholipids with higher double bond index evoke lower rigidizing and fluidizing interactions. Moreover, PL of animals fed a fat-deficient diet have less fluidity than those of control animals.Member of the Carrera del Investigador Científico, Consejo Nacional de Investìgaciones Científicas y Técnicas, Argentina.     

Effect of nutritional factors on the culture of Nostoc sp. as a source of phycobiliproteins

Summary The effect of nutritional factors in a new culture medium (BW₃) is described for the cyanobacterium Nostoc sp. The growth of Nostoc sp. was higher in BW₃ than in control media currently used for cyanobacteria. With medium BW₃ the content of the pigment c-phycocyanin depended on the culture conditions employed, particularly the nature of the nitrogen and carbon sources. Higher amounts of c-phycocyanin amounting to 20.1% on a dry-weight basis were accumulated when both sources were supplied in the gas phase of the culture. The phycobiliproteins of Nostoc sp. were resolved into two components: c-phycocyanin (_max = 614 nm) and allophycocyanin (_max = 652 nm). The phycobiliprotein composition was 30% allophycocyanin and 70% c-phycocyanin. The culture of Nostoc sp. in BW₃ medium seems promising as a source of biomass for the production of natural dyes.     

Micro-determination of amino acid composition of proteins electroblotted onto polyvinylidene difluoride membranes

A method for determination of amino acid composition of proteins separated by SDS-polyacrylamide gel electrophoresis and transferred to polyvinylidene difluoride (PVDF) membranes is described. A single blotted band containing 50 to 200 pmoles of protein was cut out and submitted to acid hydrolysis with HCl followed by derivatization with phenylisothiocyanate. The amino acid derivatives were separated by reverse phase high-performance liquid chromatography. Bovine serum albumin, lysozyme, myoglobin, ovalbumin, soybean trypsin inhibitor and carbonic anhydrase were analyzed; the results revealed a good correspondence with reported values. This can be considered an analytical method to determine the amino acid composition of samples from microquantities of protein mixtures, particularly in those cases in which SDS-polyacrylamide gel electrophoresis is the most suitable separation system.     

Microbial biomass product from apple pomace in batch and fed batch cultures

Summary Apple pomace, a solid waste from ap-ple processing industries, was used as the raw ma-terial for production of a protein enriched pro-duct. The experiments were conducted on a small scale in Erlenmeyer flasks or 4-1 fermentors in batch and fed-batch processes usingSaccharo-mycopsis lipolytica and Trichoderma reesei in sin-gle and mixed cultures. The results obtained indi-cate the technical feasibility of the process for ob-taining products containing 13% to 15% protein, on dry basis, which is adequate for cattle feed-ing.     

C6: A Monoclonal Antibody Specific for a Fibronectin Epitope Situated at the Interface between the Oncofoetal Extra-Domain B and the Repeat III8

Background

Fibronectin (FN) is a large multidomain molecule that is involved in many cellular processes. Different FN isoforms arise from alternative splicing of the pre-mRNA including, most notably, the FN isoform that contains the “extra-domain-B” (ED-B). The FN isoform containing ED-B (known as B-FN) is undetectable in healthy adult tissues but is present in large amounts in neoplastic and foetal tissues as well as on the blood vessels during angiogenesis. Thus, antibodies specific for B-FN can be useful for detecting and targeting neoplastic tissues in vivo. We previously characterised C6, a new monoclonal antibody specific for human B-FN and we suggested that it reacts with the B-C loop of the type III repeat 8 which is masked in FN isoforms lacking ED-B and that the insertion of ED-B in FN molecules unmasked it. Here we have now consolidated and refined the characterization of this B-FN specific antibody demonstrating that the epitope recognized by C6 also includes loop E-F of ED-B.

Methodology

We built the three dimensional model of the variable regions of the mAb C6 and of the FN fragment EDB-III8 and performed protein:protein docking simulation using the web server ClusPro2.0. To confirm the data obtained by protein:protein docking we generated mutant fragments of the recombinant FN fragment EDB-III8 and tested their reactivity with C6.

Conclusion

The monoclonal antibody C6 reacts with an epitope formed by the B-C loop of domain III8 and the E-F loop of ED-B. Both loops are required for an immunological reaction, thus this monoclonal is strictly specific for B-FN but the part of the epitope on III8 confers the human specificity.     

Can resistance against quorum-sensing interference be selected?

Quorum-sensing (QS) interference is a novel therapy to fight bacterial infections that, unlike conventional antibiotic treatments, is focused on reducing the damage caused by pathogens (virulence) rather than focused on inhibiting their growth. Given this ideal, it was predicted that this approach will be impervious to or at least much less prone to resistance in bacterial populations. However, recently, resistance mechanisms against well-characterized quorum quenchers (QQs) have been found in the laboratory as well as in clinical strains, demonstrating that the rise of resistance against these kinds of compounds is possible. Nevertheless, it has been argued that even if resistance mechanisms against QS interference exist, this fact does not guarantee that resistance will spread. In the present work, we discuss recent insights derived from the latest experiments to address this question. In addition, we explain how environmental conditions like the stress produced by the host immune system may influence the selection of resistance and eventually lead to the selection of QS interference-resistant bacteria in a clinical setting.