Pool sizes of fructans in roots and leaves of mycorrhizal and non-mycorrhizal barley

The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley ( Hordeum vulgare ) infected with Glomus mosseae . Treatments with and without fertilizer were included in order to distinguish between mere fertilizer effects and the effects of the symbiosis, and plants were harvested at two different time points, 35 and 50 d after planting. Fructan was the major storage carboyhdrate in both leaves and roots. The amounts of fructan were markedly altered in the mycorrhizal plants. In roots of non-fertilized mycorrhizal plants, fructan pools were significantly greater than in the corresponding non-mycorrhizal plants. By contrast, fertilization caused a general decrease in amounts of fructan in roots. The increase of fructan in mycorrhizal roots was correlated with a decrease of invertase activity. In leaves, fructan pools decreased or remained unchanged upon mycorrhizal infection; fertilization had a similar effect. However, when individual leaves of a plant were compared, intriguing effects of the mycorrhizal symbiosis could be observed. Whereas in non-mycorrhizal plants, the youngest leaves had the highest fructan contents and the oldest leaves the lowest (as previously reported), this gradient was markedly altered in mycorrhizal plants, indicating systemic effects of mycorrhiza on assimilate partitioning in shoots.     

Tetrodotoxin Interference of CNS Excitation by Glutamic Acid

TETRODOTOXIN (TTX), the powerful neurotoxin of the puffer fish, blocks electrical excitation of many neuronal and muscle membranes¹. This neurotoxin selectively blocks the sodium conductance increase, leaving the delayed potassium conductance change unaltered^2–6.     

Structural and functional heterogeneity of cytochrome c oxidase in S. cerevisiae

Respiration in Saccharomyces cerevisiae is regulated by small proteins such as the respiratory supercomplex factors (Rcf). One of these factors (Rcf1) has been shown to interact with complexes III (cyt. bc₁) and IV (cytochrome c oxidase, CytcO) of the respiratory chain and to modulate the activity of the latter. Here, we investigated the effect of deleting Rcf1 on the functionality of CytcO, purified using a protein C-tag on core subunit 1 (Cox1). Specifically, we measured the kinetics of ligand binding to the CytcO catalytic site, the O₂-reduction activity and changes in light absorption spectra. We found that upon removal of Rcf1 a fraction of the CytcO is incorrectly assembled with structural changes at the catalytic site. The data indicate that Rcf1 modulates the assembly and activity of CytcO by shifting the equilibrium of structural sub-states toward the fully active, intact form.     

Historical divergence vs. contemporary gene flow: evolutionary history of the calcicole Ranunculus alpestris group (Ranunculaceae) in the European Alps and the Carpathians

Although many species have similar total distributional ranges, they might be restricted to very different habitats and might have different phylogeographical histories. In the European Alps, our excellent knowledge of the evolutionary history of silicate‐dwelling (silicicole) plants is contrasted by a virtual lack of data from limestone‐dwelling (calcicole) plants. These two categories exhibit fundamentally different distribution patterns within the Alps and are expected to differ strongly with respect to their glacial history. The calcicole Ranunculus alpestris group comprises three diploid species of alpine habitats. Ranunculus alpestris s. str. is distributed over the southern European mountain system, while R. bilobus and R. traunfellneri are southern Alpine narrow endemics. To explore their phylogenetic relationships and phylogeographical history, we investigated the correlation between information given by nuclear and chloroplast DNA data. Analyses of amplified fragment length polymorphism fingerprints and matK sequences gave incongruent results, indicative for reticulate evolution. Our data highlight historical episodes of range fragmentation and expansion, occasional long‐distance dispersal and on‐going gene flow as important processes shaping the genetic structure of the group. Genetic divergence, expressed as a rarity index (‘frequency‐down‐weighted marker values’) seems a better indicator of historical processes than patterns of genetic diversity, which rather mirror contemporary processes as connectivity of populations and population sizes. Three phylogeographical subgroups have been found within the R. alpestris group, neither following taxonomy nor geography. Genetic heterogeneity in the Southern Alps contrasts with Northern Alpine uniformity. The Carpathians have been stepwise‐colonised from the Eastern Alpine lineage, resulting in a marked diversity loss in the Southern Carpathians. The main divergence within the group, separating the ancestor of the two endemic species from R. alpestris s. str., predates the Quaternary. Therefore, range shifts produced by palaeoclimatic oscillations seem to have acted on the genetic structure of R. alpestris group on a more regional level, e.g. triggering an allopatric separation of R. traunfellneri from R. bilobus.     

Alternative reproductive tactics and the propensity of hybridization

One explanation for hybridization between species is the fitness benefits it occasionally confers to the hybridizing individuals. This explanation is possible in species that have evolved alternative male reproductive tactics: individuals with inferior tactics might be more prone to hybridization provided it increases their reproductive success and fitness. Here we experimentally tested whether the propensity of hybridization in the wild depends on male reproductive tactic in Calopteryx splendens damselflies. Counter to our expectation, it was males adopting the superior reproductive tactic (territoriality) that had greatest propensity to hybridize than males adopting the inferior tactics (sneakers and floaters). Moreover, among the territorial males, the most ornamented males had greatest propensity to hybridize whereas the pattern was reversed in the sneaker males. Our results suggest that there is fluctuating selection on male mate discrimination against heterospecific females depending on both ornament size and the male’s reproductive tactic.     

Perspectives from early career researchers on the publication process in ecology – a response to Statzner & Resh (2010)

1. Two senior ecologists summarised their experience of the scientific publication process ( Statzner & Resh, Freshwater Biology, 2010 ; 55 , 2639) to generate discussion, particularly among early career researchers (ECRs). As a group of eight ECRs, we comment on the six trends they described. 2. We generally agree with most of the trends identified by Statzner & Resh (2010) , but also highlight a number of divergent perspectives and provide recommendations for change. Trends of particular concern are the use of inappropriate metrics to evaluate research quality (e.g. impact factor) and the salami slicing of papers to increase paper count. We advocate a transparent and comprehensive system for evaluating the research. 3. We stress the importance of impartiality and independence in the peer review process. We therefore suggest implementation of double‐blind review and quality control measures for reviewers and possibly editors. Besides such structural changes, editors should be confident to overrule biased reviewer recommendations, while reviewers should provide helpful reviews but be explicit if a submission does not meet quality standards. Authors should always conduct a thorough literature search and acknowledge historical scientific ideas and methods. Additionally, authors should report low‐quality copy editing and reviews to the editors. 4. Both early and late career researchers should jointly implement these recommendations to reverse the negative trends identified by Statzner & Resh (2010) . However, more senior scientists will always have to take the lead with respect to structural changes in the publication system given that they occupy the majority of decision‐making positions.     

A high degree of aneuploidy in frozen-thawed human preimplantation embryos

We have studied the chromosomal content in 68 normally fertilised freeze-thawed human embryos of good morphology from 34 patients with an average maternal age of 32,6 years. Forty embryos showed post-thaw cellular division and twenty-eight post-thaw cleavage arrest. After spreading of the embryos on microscope slides, analysis of chromosomes X, Y, 15, 16, 17 and 18 was performed using two rounds of fluorescent in situ hybridisation (FISH). According to the results, the embryos were divided into four groups: (I) normal, all nuclei uniformly diploid, (II) diploid mosaics, normal diploid blastomeres in combination with abnormal blastomeres, (III) abnormal, all nuclei abnormal, (IV) chaotic, the chromosome constitution varies randomly from cell to cell. Approximately 25% of the embryos had normal number of the chromosomes tested, while the majority of the embryos were abnormal. Most of the abnormal embryos were diploid mosaics (57%). This was true for the embryos showing cleavage division as well as the embryos showing cleavage arrest. Our data show a slightly higher incidence of abnormal embryos compared to those obtained with FISH in non-cryopreserved embryos and confirm that the majority of preimplantation embryos fertilised in vitro contain abnormal blastomeres. The results, mechanisms, significance and implications are discussed. Received: 19 November 1998 / Accepted: 4 March 1999     

Pathways of Proton Transfer in Cytochrome c Oxidase

During the last few years our knowledge of the structure and function of heme copper oxidases has greatly profited from the use of site-directed mutagenesis in combination with biophysical techniques. This, together with the recently-determined crystal structures of cytochrome c oxidase, has now made it possible to design experiments aimed at targeting specific pump mechanisms. Here, we summarize results from our recent kinetic studies of electron and proton-transfer reactions in wild-type and mutant forms of cytochrome c oxidase from Rhodobacter sphaeroides. These studies have made it possible to identify amino acid residues involved in proton transfer during specific reaction steps and provide a basis for discussion of mechanisms of electron and proton transfer in terminal oxidases. The results indicate that the pathway through K(I-362)/T(I-359), but not through D(I-132)/E(I-286), is used for proton transfer to a protonatable group interacting electrostatically with heme a ₃, i.e., upon reduction of the binuclear center. The pathway through D(I-132)/E(I-286) is used for uptake of pumped and substrate protons during the pumping steps during O₂ reduction.