The Glycine-Glomus-Bradyrhizobiun symbiosis. XI. Nodule gas exchange and efficiency as a function of soil and root water status in mycorrhizal soybean

Soybean [ Glycine max (L.) Merr. cv. Hobbit] plants were inoculated with a HUP− strain of Bradyrhizobium japonicum (Nitragin 61A118) and either colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol & Gerd.) Gerd. and Trappe or fertilized with KH₂PO₄ (nonVAM). They were grown for 50 days in a growth chamber and harvested over a 4-day drought period during which available soil water decreased to 0. Nodule P concentrations and P-use efficiency declined linearly with soil and root water content during the harvest period in both VAM and nonVAM plants. Nitrogenase activity, estimated from H₂ evolution and C₂H₂ reduction data, was also a linear function of declining nodule P concentrations and CO₂-exchange rates and showed simular patterns in both treatments. Hydrogen evolution and the relative efficiency of N₂ fixation, on the other hand, reacted differently to increasing drought in VAM and nonVAM plants. Differences in the responses of nodule activity in VAM and nonVAM plants to drought are interpreted in terms of demand for nodule P and carbohydrates and of the effects of dehydration on O₂ diffusion through nodule tissue.     

Focus: Addiction: Methodological and Conceptual Limitations in Exercise Addiction Research

The aim of this brief analytical review is to highlight and disentangle research dilemmas in the field of exercise addiction. Research examining exercise addiction is primarily based on self-reports, obtained by questionnaires (incorporating psychometrically validated instruments), and interviews, which provide a range of risk scores rather than diagnosis. Survey methodology indicates that the prevalence of risk for exercise addiction is approximately 3 percent among the exercising population. Several studies have reported a substantially greater prevalence of risk for exercise addiction in elite athletes compared to those who exercise for leisure. However, elite athletes may assign a different interpretation to the assessment tools than leisure exercisers. The present paper examines the: 1) discrepancies in the classification of exercise addiction; 2) inconsistent reporting of exercise addiction prevalence; and 3) varied interpretation of exercise addiction diagnostic tools. It is concluded that there is the need for consistent terminology, to follow-up results derived from exercise addiction instruments with interviews, and to follow a theory-driven rationale in this area of research.     

Computational characterisation of the interactions between human ST6Gal I and transition‐state analogue inhibitors: insights for inhibitor design

Human β‐galactoside α‐2,6‐sialyltransferase I (hST6Gal I) catalyses the synthesis of sialylated glycoconjugates involved in cell–cell interactions. Overexpression of hST6Gal I is observed in many different types of cancers, where it promotes metastasis through altered cell surface sialylation. A wide range of sialyltransferase (ST) inhibitors have been developed based on the natural donor, cytidine 5′‐monophosphate N‐acetylneuraminic acid (CMP‐Neu5Ac). Of these, analogues that are structurally similar to the transition state exhibit the highest inhibitory activity. In order to design inhibitors that are readily accessible synthetically and with favourable pharmacokinetic properties, an investigation of the replacement of the charged phosphodiester‐linker, present in many ST inhibitors, with a potential neutral isostere such as a carbamate or a 1,2,3‐triazole has been undertaken. To investigate this, molecular docking and molecular dynamics simulations were performed. These simulations provided an insight into the binding mode of previously reported phosphodiester‐linked ST inhibitors and demonstrated that targeting the proposed sialyl acceptor site is a viable option for producing selective inhibitors. The potential for a carbamate‐ or triazole‐linker as an isosteric replacement for the phosphodiester in transition‐state analogue ST inhibitors was established using molecular docking. Molecular dynamics simulations of carbamate‐ and phosphodiester‐linked compounds revealed that both classes exhibit consistent interactions with hST6Gal I. Overall, the results obtained from this study provide a rationale for synthetic and biological evaluation of triazole‐ and carbamate‐linked transition‐state analogue ST inhibitors as potential new antimetastatic agents. Copyright © 2015 John Wiley & Sons, Ltd.     

Reproducibility of Vibrionaceae population structure in coastal bacterioplankton

How reproducibly microbial populations assemble in the wild remains poorly understood. Here, we assess evidence for ecological specialization and predictability of fine-scale population structure and habitat association in coastal ocean Vibrionaceae across years. We compare Vibrionaceae lifestyles in the bacterioplankton (combinations of free-living, particle, or zooplankton associations) measured using the same sampling scheme in 2006 and 2009 to assess whether the same groups show the same environmental association year after year. This reveals complex dynamics with populations falling primarily into two categories: (i) nearly equally represented in each of the two samplings and (ii) highly skewed, often to an extent that they appear exclusive to one or the other sampling times. Importantly, populations recovered at the same abundance in both samplings occupied highly similar habitats suggesting predictable and robust environmental association while skewed abundances of some populations may be triggered by shifts in ecological conditions. The latter is supported by difference in the composition of large eukaryotic plankton between years, with samples in 2006 being dominated by copepods, and those in 2009 by diatoms. Overall, the comparison supports highly predictable population-habitat linkage but highlights the fact that complex, and often unmeasured, environmental dynamics in habitat occurrence may have strong effects on population dynamics.     

Geographical variation in reproductive character displacement in mate choice by male sailfin mollies

Female Amazon mollies, Poecilia formosa, are a unisexual species that reproduce by gynogenesis. They must coexist and mate with males of other species (usually the mollies Poecilia latipinna or Poecilia mexicana) to induce embryogenesis, but inheritance is strictly maternal. We examined the mating preference of the male sailfin molly, P. latipinna, for female sailfin mollies versus Amazon mollies, P. formosa. We compared the mating preferences of sympatric and allopatric populations collected throughout the Gulf Coast of North America. Male P. latipinna from six populations sympatric with Amazon mollies showed a significantly greater strength of preference for conspecific sailfin females than males from five populations that were allopatric with Amazon mollies. These results provide strong evidence for reproductive character displacement of male mate choice in sympatry. Furthermore, the large geographical range of populations that we tested revealed variation among populations within sympatry and allopatry, indicating that it is important to evaluate a large number of populations when examining reproductive character displacement.     

Comparative investigations on a series of [hexakis(1-(tetrazol-1-yl)alkane-N4)iron(II)] bis(tetrafluoroborate) spin crossover complexes: Methyl- to butyl-substituted species

A series of 1-(tetrazol-1-yl)alkanes [ntz] with n = 1-4 were synthesised as ligands for iron(II) spin crossover complexes. Within this series 1-(tetrazol-1-yl)butane [4tz] was prepared for the first time, whereas 1-(tetrazol-1-yl)methane [1tz], 1-(tetrazol-1-yl)ethane [2tz], 1-(tetrazol-1-yl)propane [3tz] and the [hexakis(ntz)iron(II)]bis(tetrafluoroborate) complexes were prepared according to the literature. Aiming for a comparative study we characterized all four compounds by XRPD, magnetic susceptibility measurements, ⁵⁷Fe-Moessbauer spectroscopy and IR spectroscopy. [Fe(4tz)₆](BF₄)₂ yielded appropriate single crystals and an X-ray structure of the new compound [Fe(4tz)₆](BF₄)₂ is presented. The magnetic and structural properties of all [Fe(ntz)₆](BF₄)₂ are compared and discussed.     

Sequential mate choice by multiply mating smooth newts: females become more choosy

In some species, females sequentially mate with different maleswithin a single mating period, store sperm until the eggs areeventually fertilized, and gain no other resources from themales. Halliday hypothesized that, for such species, a femalecould ensure fertilization of her eggs by mating with the firstmale that she encounters; thereafter, she can maximize the qualityof her progeny by sampling further males and by mating onlywith males of higher quality than previously mated males. Thishypothesis predicts that females' choosiness will increase asthe breeding season progresses. We tested this prediction ofHalliday's hypothesis by examining mate choice by female smoothnewts (Triturus vulgaris vulgaris). Males of this species developa dorsal crest during the courtship season. Crest height variesbetween males and is potentially an indicator of male quality.Initially, female smooth newts were equally willing to matewith males with low or high crests. However, in their secondmating, females remated only with high-crested males. Theseresults support our prediction and are consistent with Halliday'shypothesis. If crest height in smooth newts is an indicatorof quality, this change in females' mate choice criterion allowsfemales both to initiate egg-laying very early in the seasonand, subsequently, to mate preferentially with higher qualitymates     

Molecular mechanisms of thyroid dysgenesis

Thyroid dysgenesis (TD) is the most prevalent form of congenital hypothyroidism. Ttf-1, Ttf-2, Pax8 and the Tshr are expressed at early stages of thyroid development and are implicated in thyroid ontogeny. Mutations in these genes have been found in some cases of TD. The prevalence of familial forms of TD is significantly higher than expected if the disease was only sporadic, allowing to postulate a genetic basis of the disease. Linkage analysis and mutational screening of the four above-mentioned genes in familial forms of TD showed their exclusion as contributors to the disease in some families, implicating genetic heterogeneity and involving other genetic mechanisms. Strategies to uncover new genes involved in TD are therefore needed. We underscore differences in the temporal expression patterns during the human thyroid development with those in animal models. Further, the extrathyroid expression of these genes during human development enables to define the gene-specific malformations that may be present in patients bearing mutations. The data gathered on molecular thyroid development enable precise genetic counselling of affected families. By increasing our knowledge of thyroid development, we hope to uncover new perspectives of genetic screening and eventually of early in utero treatment.     

Influence of globin structures on the state of the heme. Ferrous low spin derivatives.

Studies of high spin ferrous and ferric derivatives led us to conclude that in the quaternary R structure the state of the hemes is similar to that in the free alpha and beta subunits, but in the T structure a tension acts on the hemes which tries to pull the iron and the proximal histidine further from the plane of the porphyrin. We have now studied the effect of inositol hexaphosphate (IHP) on the three low spin ferrous compounds of hemoglobin with O2, CO, and NO. IHP failed to switch the quaternary structure of carbonmonoxy- and oxyhemoglobin A to the T state, but merely caused a transition to an as yet undefined modification of the R structure. IHP is known to cause a switch to the T structure in hemoglobin Kansas. We have found that this switch induces red shifts of the visible alpha and beta absorption bands and the appearance of a shoulder on the red side of the alpha band; these changes are very weak in carbonmonoxy- and slightly stronger in oxyhemoglobin Kansas. As already noted by previous authors, addition of IHP to nitrosylhemoglobin A induces all the changes in uv absorption and CD spectra, sulfhydryl reactivities, and exchangeable proton resonances normally associated with the R leads to T transition, and is accompanied by large changes in the Soret and visible absorption bands. Experiments with nitrosyl hybrids show that these changes in absorption are caused predominantly by the hemes in the alpha subunits. In the accompanying paper Maxwell and Caughey (J. C. Maxwell and W. S. Caughey (1976), Biochemistry, following paper in this issue) report that the NO in nitrosylhemoglobin without IHP gives a single ir stretching frequency characteristic for six-coordinated nitrosyl hemes; addition of IHP causes the appearance of a second ir band, of intensity equal to that of the first, which is characteristic for five-coordinated nitrosyl hemes. Taken together, these results show that the R leads to T transition causes either a rupture or at least a very dramatic stretching of the bond from the iron to the heme-linked histidine, such that an equilibrium is set up between five- and six-coordinated hemes, biased toward five-coordinated hemes in the alpha and six-coordinated ones in the beta subunits. The reason why IHP can switch nitrosyl-, but not carbonmonoxy- or oxyhemoglobin A, from the R to the T structure is to be found in the weakening of the iron-histidine bond by the unpaired NO electron and by the very short Fe-NO bond length.