Cadmium exerts its toxic effects on photosynthesis via a cascade mechanism in the cyanobacterium,Synechocystis PCC 6803

Despite intense research, the mechanism of Cd²⁺ toxicity on photosynthesis is still elusive because of the multiplicity of the inhibitory effects and different barriers in plants. The quick Cd²⁺ uptake in Synechocystis PCC 6803 permits the direct interaction of cadmium with the photosynthetic machinery and allows the distinction between primary and secondary effects. We show that the CO₂‐dependent electron transport is rapidly inhibited upon exposing the cells to 40 µm Cd²⁺ (50% inhibition in ～15 min). However, during this time we observe only symptoms of photosystem I acceptor side limitation and a build of an excitation pressure on the reaction centres, as indicated by light‐induced P700 redox transients, O₂ polarography and changes in chlorophyll a fluorescence parameters. Inhibitory effects on photosystem II electron transport and the degradation of the reaction centre protein D1 can only be observed after several hours, and only in the light, as revealed by chlorophyll a fluorescence transients, thermoluminescence and immunoblotting. Despite the marked differences in the manifestations of these short‐ and long‐term effects, they exhibit virtually the same Cd²⁺ concentration dependence. These data strongly suggest a cascade mechanism of the toxic effect, with a primary effect in the dark reactions.     

Host‐specific morphologies but no host races in the commensal bivalve Neaeromya rugifera

Speciation by host shift is one of the explicit models of ecological speciation. A prerequisite of this model is the formation of host races (sympatric populations that show host‐specific genetic structuring and phenotypes). Many members of the diverse marine bivalve superfamily Galeommatoidea have obligate commensal relationships with invertebrate hosts. Some species have the ability to occupy multiple host species, thereby providing potential opportunities to test for the formation of host races. The Northeast Pacific galeommatoidean Neaeromya rugifera attaches to two strikingly different hosts: the blue mud shrimp Upogebia pugettensis and the polychaete sea mouse Aphrodita spp. We tested if this host difference has resulted in the formation of host races using shell morphologies and genetic markers. We found that populations from different hosts differ significantly in shell morphology. However, based on mitochondrial makers, N. rugifera showed no distinct host‐specific genetic structuring, indicating the existence of a panmictic population. We conclude that the host‐specific morphologies these clams exhibit may reflect ecophenotypic plasticity rather than the existence of host races, but this needs to be corroborated with additional genetic data and larger sample sizes. The pronounced conchological variation within N. rugifera calls for further investigation of its taxonomic relationship with its poorly studied, but morphologically similar, sympatric congener Neaeromya compressa.     

Correlated pedigree and molecular estimates of inbreeding and their ability to detect inbreeding depression in the Icelandic sheepdog, a recently bottlenecked population of domestic dogs

We examine the relationship of the inbreeding coefficient (f) and molecular estimates of inbreeding (IR, sMLH) in the Icelandic sheepdog. The breed experienced a severe genetic bottleneck and near extinction in the last century. Molecular estimates and the inbreeding coefficient are significantly correlated despite the moderate number of markers and individuals used in this study. This is most likely an effect of the extreme relatedness and relatively high variance in individual inbreeding coefficients in the population. There is a significant relationship between inbreeding (f) and the occurrence of hip dysplasia. However, the molecular measures did not detect hip dysplasia as an inbreeding effect.     

Estimation of coancestry in Iberian pigs using molecular markers

Genetic markers provide a useful tool toestimate pairwise coancestry betweenindividuals in the absence of a known pedigree. Inthe present work 62 pigs from two relatedstrains of Iberian breed, Guadyerbas andTorbiscal, belonging to a conservationprogramme with completely known pedigrees since1945, have been genotyped for 49microsatellites. Four coefficients thatsummarise molecular resemblance betweenindividuals together with eightestimators of coancestry have been calculatedfrom this information. Their values werecompared with the genealogical coancestry,calculated from the complete or partialpedigree. The eight estimations obtained usingmolecular information substantiallyunderestimate the coancestry calculated usingthe genealogical analysis. The correlationbetween the estimates and the genealogicalvalues was also calculated. This correlationwas high, between 0.78 and 0.93 for differentestimators, when all pairwise comparisons amongthe 62 animals were considered. However, thecorrelation decreases remarkably to 0.49–0.69and 0.37–0.47 for the Guadyerbas and Torbiscalpopulations respectively, when they wereanalysed separately. All the correlations weresimilar to those obtained when using simplecoefficients of molecular resemblance such asmolecular coancestry or similarity indexes.Finally, simulations were carried out tofurther explore the results obtained. It isconcluded that lack of information on theallele frequencies in the base population mayexplain the bias of these estimators inpopulations with complex pedigrees.     

Dinucleotide microsatellite DNA loci from the ant Myrmica scabrinodis

We describe the isolation and characterization of five dinucleotide microsatellite loci in the ant Myrmica scabrinodis, which were obtained using a magnetic bead hybridization selection protocol. The PCR primers were tested on nine to 11 individuals. The number of alleles ranged from two to 13, and the observed heterozygosity from 0.200 to 0.778.     

Extracellular release of photosynthetic products by freshwater phytoplankton populations, with special reference to the algal species involved

SUMMARY. Over three successive years, depth profiles of C-fixation and excretion, chlorophyll- a concentrations, phytoplankton species composition and bacterial numbers were determined in Lake Vechten, a slightly eutrophic lake in The Netherlands. Special attention was given to the method used to measure extracellular release.
Excretion of dissolved organic ¹⁴C depended largely upon the photo-synthetic activity of the phytoplankton, ranging from 0–2.5 mg m^-1 h^-1, representing a percentage extracellular release (PER) of 0–25%.
During a period in August, however, a subsurface chlorophyll- a maximum at 5–7 m depth coincided with high excretion rates of up to 10 mg Cm^-3 h^-1 (PER = 55%). Phytoplankton analysis revealed a stratification in numbers of Mallomonas caudata with a maximum at 5–7 m depth.
The results suggest that in these water layers bacterial populations grew at the expense of the dissolved organic carbon compounds excreted by Mallomonas caudata. This means that extracellular release can temporarily function as an important nutrient source for the heterotrophie community in addition to the more or less constant dissolved organic carbon pool.     

Studies on Fusarium-Gladiolus Interactions

Using standardized conditions, 65 genotypes of Gladiolus were screened for Fusarium resistance. High levels were found in 'large-flowered" types, Primulinus hybrids, G. callianthus, G. garnierii , and G. dalenii. Some accessions of G. dalenii exhibited no disease symptoms when inoculated with two standard test isolates. No resistance was found in 'small-flowered' types. To estimate race-specifity of the resistance, eight highly resistant Gladiolus genotypes were tested in an in vitro test against 43 isolates of F. oxysporum f.sp. gladioli. Two isolates were able to partially infect the G. dalenii accessions and this was confirmed using whole plants. Implications for resistance breeding are discussed.     

Neuromodulating Attention and Mind-Wandering Processes with a Single Session Real Time EEG

Our minds are continuously alternating between external attention (EA) and mind wandering (MW). An appropriate balance between EA and MW is important for promoting efficient perceptual processing, executive functioning, decision-making, auto-biographical memory, and creativity. There is evidence that EA processes are associated with increased activity in high-frequency EEG bands (e.g., SMR), contrasting with the dominance of low-frequency bands during MW (e.g., Theta). The aim of the present study was to test the effects of two distinct single session real-time EEG (rtEEG) protocols (SMR up-training/Theta down-training—SMR?Theta?; Theta up-training/SMR down-training—Theta?SMR?) on EA and MW processes. Thirty healthy volunteers were randomly assigned to one of two rtEEG training protocols (SMR?Theta?; Theta?SMR?). Before and after the rtEEG training, participants completed the attention network task (ANT) along with several MW measures. Both training protocols were effective in increasing SMR (SMR?Theta?) and theta (Theta?SMR?) amplitudes but not in decreasing the amplitude of down-trained bands. There were no significant effects of the rtEEG training in either EA or MW measures. However, there was a significant positive correlation between post-training SMR increases and the use of deliberate MW (rather than spontaneous) strategies. Additionally, for the Theta?SMR? protocol, increase in post-training Theta amplitude was significantly associated with a decreased efficiency in the orientation network.     

Growth Regulators in Picea abies

The occurrence of growth regulators active in the Avena coleoptile straight-growth test in sprouting buds and seedlings of Norway spruce (Picea abies Karst.) was investigated. The acid ether fraction contained a growth stimulator, the Rf of which in isopropanol: ammonia: water was 0.2–0.4. This substance behaved as indole-3-acetic acid (IAA) in elec-trophoresis, in chromatography in various solvent systems on paper and on a Sephadex column. It gave the colour typical of IAA when sprayed with Ehrlich reagent and its fluorescence characteristics corresponded to IAA. Acid ether-soluble inhibitors showed most activity at Rf 0.4–0.7, but due to tailing they interfered with the determination of the stimulator at the Rf of IAA in the bioassay. They also masked the activity of other stimulators. Colour reactions were obtained with Ehrlich reagent in the inhibiting chromatogram zone. When eluates from this zone were tested in high dilutions or after gel filtration growth stimulation was obtained. The acid fraction of seedling shoots also contained a stimulator with Rf 0.7–0.8. In the neutral-basic ether-soluble fraction growth stimulation was obtained at Rf 0.5–0.7. The extracts also contained stimulatory substances insoluble in ether but soluble in n-butanol and partly in ethyl acetate. When the butanol fraction was hydrolyzed in 1 M NaOH a substance behaving as IAA when chromatographed was released.