Extensive expression regulation and lack of heterologous enzymatic activity of the Class II trehalose metabolism proteins from Arabidopsis thaliana

Trehalose metabolism has profound effects on plant growth and metabolism, but the mechanisms involved are unclear. In Arabidopsis , 21 putative trehalose biosynthesis genes are classified in three subfamilies based on their similarity with yeast TPS1 (encoding a trehalose-6-phosphate synthase, TPS) or TPS2 (encoding a trehalose-6-phosphate phosphatase, TPP). Although TPS1 (Class I) and TPPA and TPPB (Class III) proteins have established TPS and TPP activity, respectively, the function of the Class II proteins (AtTPS5-AtTPS11) remains elusive. A complete set of promoter- β -glucurinidase/green fluorescent protein reporters demonstrates their remarkably differential tissue-specific expression and responsiveness to carbon availability and hormones. Heterologous expression in yeast furthermore suggests that none of the encoded enzymes displays significant TPS or TPP activity, consistent with a regulatory rather than metabolic function for this remarkable class of proteins.     

Spatial genetic analysis of the grass snake,Natrix natrix (Squamata: Colubridae), in an intensively used agricultural landscape

Both the conversion of natural habitats to farmland and efforts at increasing the yield of existing crops contribute to a decline in biodiversity. As a consequence of land conversion, specialised species are restricted to remnants of original habitat patches, which are frequently isolated. This may lead to a genetic differentiation of the subpopulations. We used seven microsatellite markers to examine the genetic population structure of the grass snake, Natrix natrix (Linnaeus, 1758), sampled in remnants of pristine habitat embedded in an intensively used agricultural landscape in north‐western Switzerland. The study area, a former wetland, has been drained and gradually converted into an agricultural plain in the last century, reducing the pristine habitat to approximately 1% of the entire area. The grass snake feeds almost entirely on amphibians, and is therefore associated with wetlands. In Central Europe, the species shows severe decline, most probably as a result of wetland drainage and decrease of amphibian populations. We found no genetically distinct grass snake populations in the study area covering 90 km². This implies that there is an exchange of individuals between small remnants of original habitat. Thus, gene flow may prevent any genetic differentiation of subpopulations distributed over a relatively large area. Our results show that a specialized snake species can persist in an intensively used agricultural landscape, provided that suitable habitat patches are interconnected. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 51–58.     

Phylogeographic structure in the gilgie (Decapoda: Parastacidae: Cherax quinquecarinatus): a south‐western Australian freshwater crayfish

The gilgie (Cherax quinquecarinatus) is among the more widespread of the six endemic south‐western Australian freshwater crayfish species. In the present study, the phylogeographic structure of the gilgie was investigated across its distribution to determine whether patterns reflected those identified earlier in a co‐distributed congeneric, the koonac (Cherax preissii). Gilgies were sampled from 20 localities, a 412‐bp fragment of the cytochrome c oxidase subunit I mitochondrial DNA gene was amplified from 75 individuals, and allozyme variation was assayed at nine loci. As in the koonac, three geographically‐restricted lineages were identified: from the north‐western, southern coastal, and intermediate/south‐western regions. Phylogeographic breaks appeared to be congruent with those in the koonac. The extent of genetic differentiation among lineages was comparable to that in the koonac, suggesting temporal congruence of the historical events responsible for the observed structure. A relaxed Bayesian molecular clock suggested that the major clades and lineages in each species diverged in the Late Miocene–Early Pliocene (4.0–9.6 Myr ago), possibly resulting from increasing pulses of aridity. The retrieval of almost‐identical phylogeographic structure in two co‐distributed species suggests that biogeographic regions can be more accurately defined in south‐western Australia. With the geographic fidelity of these lineages, the present data also provide evidence of the translocation of a single individual from the north‐west to the south coast. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 385–402.     

Personality disorder: a new global perspective

Personality disorder is now being accepted as an important condition in mainstream psychiatry across the world. Although it often remains unrecognized in ordinary practice, research studies have shown it is common, creates considerable morbidity, is associated with high costs to services and to society, and interferes, usually negatively, with progress in the treatment of other mental disorders. We now have evidence that personality disorder, as currently classified, affects around 6% of the world population, and the differences between countries show no consistent variation. We are also getting increasing evidence that some treatments, mainly psychological, are of value in this group of disorders. What is now needed is a new classification that is of greater value to clinicians, and the WPA Section on Personality Disorders is currently undertaking this task.     

Evolutionary Conservation in Retinoid Signalling and Metabolism

In accord with the notion that retinoid signalling is of centralimportance in vertebrate evolution, a number of its componentsare evolutionarily conserved. Retinoid X nuclear receptors (RXRs),which interact directly with a number of signalling pathways,are highly conserved among mammals, Xenopus, and chick. We havestudied RXRs in zebrafish and find that they are also very wellconserved with respect to amino acid sequence and function,compared to mammalian RXRs. However, zebrafish has additionalsubtypes (RXR and RXR) which are altered in structure and function.New information which has come to light since these were firstdescribed suggests ways in which these unique subtypes couldfine-tune retinoid signalling in zebrafish. We have performedphylogenetic analysis with the zebrafish RXRs and RXRs fromother species to try to understand the evolutionary relationshipsamong them. In addition, we have found a retinoic acid (RA)-inducible,RA-metabolizing cytochrome P450 (P450RAI/CYP26) which is evolutionarilyconserved among vertebrates and has an important role in controllingretinoid signalling by regulating the level of biologicallyavailable RA.     

Dunaliella acidophila: an algae with a positive zeta potential at its optimal pH for growth*

Abstract. The zeta potential (which approximates the surface potential) of the acid resistant green alga Dunaliella acidophila (optimal growth at pH 1.0) and the salt resistant D. parva (grown at pH 7.6) were calculated from the electrophoretic mobility of cells as determined by means of free-flow electrophoresis. Dunaliella acidophila cells exhibit a positive zeta potential (+5 to +20mV) at acidic external pH values, whereas negative zeta potentials (-30 mV) were measured at neutral pH values. Negative zeta potentials of the same order of magnitude were also measured for D. parva cells (pH 7.6). Low concentrations of La³⁺ and A1³⁺ did not affect the positive zeta potential of D. acidophila at acidic pH values, whereas higher concentrations caused a shift to more positive potentials. However, at neutral pH these cations caused a significant decrease of the negative zeta potential. The impermeant polycation poly-L-lysine acted in a similar manner to A1³⁺ or La³⁺. The effect of Impermeant cations and anions on various physiological reactions also supports the existence of a positive zeta potential for D. acidophila and of a negative zeta potential for D. parva: polycations such as DEAE-dextran and poly-L-lysine strongly inhibitied photosynthesis and mobility of D. parva, but did not affect these reactions in D. acidophila. Comparable differential inhibitions were also observed for A1³⁺ and La³⁺. Impermeant anions such as Dextran-sulfate exhibited effects in the opposite direction: inhibition was stronger with D. acidophila and weaker with D. parva. However, the differential inhibition by impermeant anions was much less pronounced in comparison with impermeant cations due to the relatively high pK_a values of anionic solutes and consequently relatively high protonation at pH 1.0. The physiological consequences of an asymmetrically charged plasma membrane (excess of positive charges outside, excess of negative charges on the cytoplasmic side) of D. acidophila are discussed in regard to the extreme acid resistance of this alga and its resistance to cationic toxic solutes in industrial wastes.     

The effects of potential larval supply, settlement and post-settlement processes on the distribution of two species of filter-feeding caddisflies

1. Hydropsychid caddisfly larvae are often abundant in fast flow habitats and on highly textured substrata. Such patterns are usually inferred to result from habitat preference, but the roles of larval supply to the benthos and post‐settlement events are rarely examined for stream populations. We describe a manipulative field experiment that examined larval supply, habitat preference and post‐settlement events simultaneously for two co‐occurring species of hydropsychids. 2. Ten artificial channels were constructed in a natural riffle to create fast and slow flow habitats and within each channel we placed six artificial substrata whose surfaces had been modified to create three different texture treatments. We measured discharge through channels and monitored hydropsychid colonisation of substrata every 3–4 days. Half of the substrata had all hydropsychids and nets removed every 3–4 days (short‐term colonisation) whereas the remaining half were counted but nets and hydropsychids left attached (long‐term colonisation). Short‐term counts of nets and individuals were summed to allow comparison with long‐term colonisation substrata. 3. Smicrophylax sp. AV2 larvae were more abundant in fast flow channels than slow flow channels, but these differences were proportional to discharge through each of the channels, suggesting that supply of settlers can explain this pattern. Smicrophylax larvae were least abundant on smooth substrata, which suggests that this species selects habitats based on surface texture. Alternatively, Asmicridea sp. AV1 larvae were only found in fast flow channels and this most likely reflects an active habitat choice by this species, but there was no significant difference between different texture treatments. 4. There were no differences between summed, short‐ and long‐term counts of recruits for either species, but there were more nets than larvae, especially in slow flow channels, by the end of the experiment, suggesting that larval mortality or re‐dispersal after settlement could be considerable. 5. Our results indicate that supply, habitat selection at settlement and post‐settlement processes all contributed variously to the distribution of hydropsychid caddisfly larvae, but that each species was affected differentially by these factors. Larval supply and post‐settlement processes are rarely examined by stream researchers and our results demonstrate these factors deserve much more consideration. Calculating accurate larval supply rates to sites is challenging, but we suggest that such detailed information is necessary if we are to sort out what sets limits to distributions and the underlying population structure of stream invertebrate populations.     

Comparison of measured and EF5-r-derived N2O fluxes from a spring-fed river

There is considerable uncertainty in the estimates of indirect N₂O emissions as defined by the intergovernmental panel on climate change's (IPCC) methodology. Direct measurements of N₂O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N₂O budget. The objectives of this research were to measure the N₂O fluxes from a spring‐fed river, relate these fluxes to the dissolved N₂O concentrations and NO₃‐N loading of the river, and to try and define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N₂O L^?1. River NO₃‐N and dissolved N₂O concentrations ranged from 2.5 to 5.3 mg L^?1 and 0.4 to 1.9 μg N₂O‐N L^?1, respectively, with N₂O saturation reaching 404%. Floating headspace chambers were used to sample N₂O fluxes. N₂O‐N fluxes were significantly related to dissolved N₂O‐N concentrations (r²=30.6) but not to NO₃‐N concentrations. The N₂O‐N fluxes ranged from 38–501 μg m^?2 h^?1, averaging 171 μg m^?2 h^?1 (±SD 85) overall. The measured N₂O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N₂O present in the groundwater that fed the river.     

Evolutionary Modifications of the Spiralian Developmental Program

SYNOPSIS. The Spiralia, an assemblage of phyla united by theirstereotypic pattern of early embryonic cell divisions (spiralcleavage), is an interesting group in which to investigate theevolution of development. This paper examines modificationsof developmental mechanisms within the Spiralia with emphasison the basallybranching forms. Although demonstrating a notabledegree of evolutionary conservation, the equal quartet cleavagepattern, which appears to be the ancestral condition, nonethelessexhibits modifications within the various spiralian groups,such as unequal cleavage, changes in cell size and rate of division,formation of two rather than four quadrants (duet spiral cleavage),and in extreme cases the loss of any trace of the spiral pattern.While the cell lineages of spiralians are remarkably conserved,one can discern evolutionary changes, for example in the cellsthat give rise to mesodenn. Studies of blastomere specificationin many spiralian groups and analyses of axis determinationindicate that embryos with equal versus unequal cleavage typicallyuse different determinative mechanisms to establish cell fatesand the dorsoventral axis. These properties are establishedearly in species exhibiting unequal cleavage. While previousexperiments suggested that equal cleavage was associated withlate specification, there is now evidence of precocious specificationof quadrant fates in some equal-cleaving species, such as thenemerteans and the polyclad turbellarians     

Xylem water transport: is the available evidence consistent with the cohesion theory?

Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m⁻¹. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants.