Plant responses to rising water tables and nutrient management in calcareous dune slacks

Plant species of oligotrophic wet dune slacks have dramatically decreased as a result of desiccation and eutrophication. The aim of this study was to test in a field experiment the effects of restoration management in oligotrophic, wet dune slacks (groundwater level rise in combination with topsoil removal or mowing) on abiotic variables and on survival and biomass of four plant species. The effect of groundwater level rise on abiotic variables strongly differed between mown sampling locations and those with topsoil removal. At locations with a mowing treatment, a large rise in water tables led to increased N availability and higher reduced iron concentrations than at other locations. Such effects were absent at locations with recent topsoil removal. No effect of groundwater level rise on P-availability was found. Topsoil removal on average lowered N availability by 13%, P availability by 65% and Fe²⁺ by 56%. All phytometer species survived better in mown dune slacks than in dune slacks that had received topsoil removal. Survival of all species was negatively related to groundwater level rise. On the short term local extinction risks of small populations may be enhanced by rewetting and topsoil removal. On the long-term, however, such measures are crucial to maintain vegetation of oligotrophic wet dune slacks in a degraded dune landscape.     

Gene prioritization through genomic data fusion

The identification of genes involved in health and disease remains a challenge. We describe a bioinformatics approach, together with a freely accessible, interactive and flexible software termed Endeavour, to prioritize candidate genes underlying biological processes or diseases, based on their similarity to known genes involved in these phenomena. Unlike previous approaches, ours generates distinct prioritizations for multiple heterogeneous data sources, which are then integrated, or fused, into a global ranking using order statistics. In addition, it offers the flexibility of including additional data sources. Validation of our approach revealed it was able to efficiently prioritize 627 genes in disease data sets and 76 genes in biological pathway sets, identify candidates of 16 mono- or polygenic diseases, and discover regulatory genes of myeloid differentiation. Furthermore, the approach identified a novel gene involved in craniofacial development from a 2-Mb chromosomal region, deleted in some patients with DiGeorge-like birth defects. The approach described here offers an alternative integrative method for gene discovery.     

Does initial litter chemistry explain litter mixture effects on decomposition?

Abstract We tested the hypothesis that interactions in litter mixtures (expressed as the difference between observed and expected decomposition rates) are greater when the component species differ more in their initial litter chemistry. Thereto, we collected freshly senesced leaf litter from a wide range of species from an old field and woodland vegetation, and a fen ecosystem in The Netherlands. Litterbags with either mono-specific litter (20 and 15 species), or litter mixtures (50 and 42 species pairs) of randomly drawn combinations of two representatives from different plant functional types were incubated for 20, 35 and 54 weeks in a purpose-built decomposition bed (woodland/old field) or in the field (fen). Species showed a wide range of decomposition rates. For the woodland/old field species, initial litter C and P concentrations were significantly correlated with litter decomposition rate. For the fen species, litter phenolics concentration was correlated with decomposition rate. If the Sphagnum species were left out of the analyses, initial litter P and phenolics concentration both showed a significant relationship, albeit only with the remaining mass after 1 year. Differences between observed and expected decomposition were often considerable in individual litter mixtures. Regression analysis showed that such differences were not related to the differences in litter chemistry of the component species. Furthermore, litter mixtures containing species with very different initial litter chemistry did not show stronger interaction when tested against litter mixtures containing chemically similar litter types. From these observations we conclude that the difference in initial single litter chemistry parameters of the component is not a useful concept to explain interactions in litter mixtures.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Differential microorganism-induced mannose-binding lectin activation

Mannose-binding lectin (MBL) is a serum complement factor playing a dominant role in first-line defense. When MBL binds to specific sugar moieties on microorganisms, the lectin complement pathway (LCP) is activated. Changes in the mbl gene and promotor may result in MBL with less activity, predisposing the individual to recurrent infections. Using a functional MBL assay, we investigated at what concentration different microbes activated MBL. Less than 1 colony-forming unit (CFU) of Neisseria meningitidis groups B and C still activated MBL, which may be ascribed to filterable blebs. Nocardia farcinica and Legionella pneumophila activated MBL well, which raises new questions about host susceptibility. In contrast to other research, Pseudomonas aeruginosa activated the LCP potently.     

Integration of chicken genomic resources to enable whole-genome sequencing

Different genomic resources in chicken were integrated through the Wageningen chicken BAC library. First, a BAC anchor map was created by screening this library with two sets of markers: microsatellite markers from the consensus linkage map and markers created from BAC end sequencing in chromosome walking experiments. Second, HINdIII digestion fingerprints were created for all BACs of the Wageningen chicken BAC library. Third, cytogenetic positions of BACs were assigned by FISH. These integrated resources will facilitate further chromosome-walking experiments and whole-genome sequencing.     

Cross-adaptation and molecular modeling study of receptor mechanisms common to four taste stimuli in humans

Psychophysical cross-adaptation experiments were performed with two carbohydrates, sucrose (SUC) and fructose (FRU), and two sweeteners, acesulfame-K (MOD) and dulcin (DUL). Seven subjects were asked to match concentrations that elicited the same intensity as a sucrose reference (30 g/l). Cross-adaptation levels were calculated as the ratio of isointense concentrations measured for a given stimulus before and under adaptation. On average, cross-adaptation between SUC and FRU is low and apparently reciprocal. By contrast, cross-adaptation between SUC and MOD is clearly non-reciprocal: SUC adapts MOD significantly (24%, P < 0.005), but MOD fails to adapt SUC (2%, P < 0.79). Significant and reciprocal cross-enhancement is observed between DUL and MOD (approximately -20%, P < 0.03), and also between SUC and DUL (approximately -15%, P < 0.08). In parallel, molecular modeling of the four tastants was performed in order to look for the 12 common binding motifs that were isolated on 14 other tastants in a previous study. SUC and FRU each display 10 out of the 12 binding motifs, whereas DUL and MOD only display four and five distinct motifs respectively and do not have any motif in common. Experimental cross-adaptation levels seem to correlate well with the number of motifs that molecules have in common. FRU and SUC share a majority of binding motifs and correlatively show mutual cross-adaptation. Four motifs of MOD are found among the 10 motifs of SUC, which may explain why SUC cross-adapts MOD but not vice versa. By contrast, DUL and MOD do not share any motif and do not cross- adapt. The various molecular mechanisms that may be responsible for cross-adaptation and/or cross-enhancement are discussed in light of our results.      

Vertical jumping in Galago senegalensis: the quest for an obligate mechanical power amplifier

Bushbabies (Galago senegalensis) are renowned for their phenomenal jumping capacity. It was postulated that mechanical power amplification must be involved. Dynamic analysis of the vertical jumps performed by two bushbabies confirms the need for a power amplifier. Inverse dynamics coupled to a geometric musculo-skeletal model were used to elucidate the precise nature of the mechanism powering maximal vertical jumps. Most of the power required for jumping is delivered by the vastus muscle-tendon systems (knee extensor). Comparison with the external joint-powers revealed, however, an important power transport from this extensor (about 65%) to the ankle and the midfoot via the bi-articular calf muscles. Peak power output likely implies elastic recoil of the complex aponeurotic system of the vastus muscle. Patterns of changes in length and tension of the muscle-tendon complex during different phases of the jump were found which provide strong evidence for substantial power amplification (times 15). It is argued here that the multiple internal connective tissue sheets and attachment structures of the well-developed bundles of the vastus muscle become increasingly stretched during preparatory crouching and throughout the extension phase, except for the last 13 ms of the push-off (i.e. when power requirements peak). Then, tension in the knee extensors abruptly falls from its maximum, allowing the necessary fast recoil of the tensed tendon structures to occur.     

Demonstration of the existence of a second,non-lysosomal glucocerebrosidase that is not deficient in Gaucher disease

In addition to the lysosomal glucocerebrosidase, a distinct β-glucosidase that is also active towards glucosylceramide could be demonstrated in various human tissues and cell types. Subcellular fractionation analysis revealed that the hitherto undescribed glucocerebrosidase is not located in lysosomes but in compartments with a considerably lower density. The non-lysosomal glucocerebrosidase differed in several respects from lysosomal glucocerebrosidase. The non-lysosomal isoenzyme proved to be tightly membrane-bound, whereas lysosomal glucocerebrosidase is weakly membrane-associated. The pH optimum of the non-lysosomal isoenzyme is less acidic than that of lysosomal glucocerebrosidase. Non-lysosomal glucocerebrosidase, in contrast to the lysosomal isoenzyme, was not inhibited by low concentrations of conduritol B-epoxide, was markedly inhibited by taurocholate, was not stimulated in activity by the lysosomal activator protein saposin C, and was not deficient in patients with Gaucher disease. Non-lysosomal glucocerebrosidase proved to be less sensitive to inhibition by castanospermine or deoxynojirimycin but more sensitive to inhibition by D-gluconolactone than the lysosomal glucocerebrosidase. The physiological function of this second, non-lysosomal, glucocerebrosidase is as yet unknown.