Genotype-specific interactions and the trade-off between host and parasite fitness

Background  

Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana.     

Putative candidate genes for blood pressure control in the SHR.BN-RNO8 congenic substrains

The SHR-Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene (Kcnj1) and brain dopamine receptor 2 gene (Drd2). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR-Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 (Sm22) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR-Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR-Lx) intercross population.     

Hydrogenase activity in aged, nonviable Desulfovibrio vulgaris cultures and its significance in anaerobic biocorrosion

Batch cultures of Desulfovibrio vulgaris stored at 32 degrees C for 10 months have been found to retain 50% of the hydrogenase activity of a 1-day culture. The hydrogenase found in old cultures needs reducing conditions for its activation. Viable cell counts are negative after 6 months, showing that the hydrogenase activity does not depend on the presence of viable cells. These observations are of importance in the understanding of anaerobic biocorrosion of metals caused by depolarization phenomena.     

Growth and Photosynthetic Characteristics of Solanum tuberosum Plantlets Cultivated in Vitro in Different Conditions of Aeration, Sucrose Supply, and CO(2) Enrichment

Growth characteristics, oxygen exchange, and carbohydrate and chlorophyll contents were determined 30 days after subculturing of single node-derived plantlets of Solanum tuberosum cv Haig cultivated in vitro. Cultivation conditions were: (a) photomixotrophy in closed vessel, (b) photomixotrophy in closed vessel on medium supplemented with silver thiosulfate, (c) photomixotrophy in aerated vessel, (d) photoautotrophy in air, (e) photoautotrophy in CO₂-enriched air. In photomixotrophic conditions, aeration of the vessel enhanced sucrose utilization and had a positive effect on plantlet growth. In photoautotrophic conditions, growth of the plantlets was slow in air and was strongly enhanced by CO₂ enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouse plant leaves. In high light, however, plantlets grown photoautotrophically in a CO₂-enriched atmosphere had higher oxygen exchange rates. We concluded from these results that potato plantlets in vitro in conditions (c), (d), and (e) developed C3-plant photosynthetic characteristics, which were in photoautotrophically grown plantlets comparable to those of field-grown plants.     

Effects of extremely low frequency (ELF) electric fields on cell growth and DNA repair in human skin fibroblasts

A number of physical and chemical agents in the environment have been studied for their ability to induce or alter DNA repair mechanisms in human cells. We have investigated the effects of 60 Hz, 1000 V/cm electric fields on DNA repair in normal human fibroblasts in vitro. An examination was done on the ability of electric fields suspected to cause damage which could be repaired by thymine dimer excision and measurable by the bromodeoxyuridine photolysis assay. The thymine dimer assay with enzyme-sensitive site analysis was used to measure the cells' capacity for removing ultraviolet light (u.v.)-induced pyrimidine dimers; during exposure to electric field 24 hr before u.v. irradiation; 24 hr after u.v. irradiation; and up to 48 hr continuously after u.v. irradiation. Cell growth and cell survival following electric field exposure were also studied. Within the limits of these experiments, it was found that exposure to such electric fields did not alter cell growth or survival, and no DNA repair or alteration in DNA excision repair capacity was observed as compared with unexposed control cultures.     

Investigation of polylysine-dipalmitoylphosphatidylglycerol interactions in model membranes

The effect of poly(L-lysine) on dipalmitoylphosphatidylglycerol bilayers has been studied by Raman and infrared spectroscopies, small-angle X-ray diffraction, and carboxyfluorescein escape experiments. The polypeptide is shown to induce a stabilization of the bilayer detected by the increase of interchain vibrational coupling and a slight decrease of the overall disorder. In addition, long polylysine (Mr 150,000) induces a positive shift of the gel to fluid transition temperature and, at lipid to lysine molar ratios greater than 1, a lateral phase separation within the bilayer. Raman and infrared spectra indicate modifications at the head group level. In contrast, short polylysine (Mr 4,000) leads to a decrease of the lipid thermotropic transition temperature, and no modification of the polar head group and no phase separation could be observed. These differences between short and long polypeptides are correlated with the conformation the polypeptide adopts upon binding to the lipid, which favors the formation of alpha-helices in the case of long polypeptides (Mr greater than or equal to 14,000). The X-ray data suggest that the basic polypeptide acts as a bridge between neighboring bilayers, thus causing their aggregation and dehydration.     

Partial characterization and solubilization of receptors for atrial natriuretic factor in rat glomeruli

Specific receptors for atrial natriuretic factor (ANF) have been identified and solubilized in glomeruli from rat kidney. Radioiodinated synthetic ANF (Arg 101-Tyr 126) bound to a single class of high affinity (Kd 27 +/- 24 pM) sites with a density of 390 +/- 230 fmole/mg protein. The binding was time- and temperature-dependent, saturable and reversible. The ANF-receptor complex was not affected by angiotensin II, ACTH or vasopressin. Solubilization with 10 mM 3-[(3-cholamidopropyl)-dimethylammonio]- 1-propane sulfonate (CHAPS) slightly increased the affinity for ANF (Kd 5.0 +/- 3.3 pM) without affecting the density (250 +/- 110 fmole/mg protein). Similar results were found with 1% Triton X-100. ANF-related peptides interact generally in the same way with non-solubilized and solubilized receptors, indicating a fully preserved specificity of the receptors.     

Photosynthesis by developing embryos of oilseed rape (Brassica napus L.)

The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO₂-dependent O₂ evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO₂-dependentO₂ evolution, per unit chlorophyll, and CO₂ saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO₂-dependent O₂ evolution(90–100 mol mg^–1 chlorophyll h^–1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m^–2 s^–1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L.