Factors toxic to beech (Fagus sylvatica L.) seedlings in acid soils

The effects of highly and moderately acid soils on total biomass, biomass partitioning, fine root characteristics and nutritional status of beech seedlings (Fagus sylvatica L.) were studied in a growth chamber experiment. In Haplic Arenosols seedlings grew slowly but equally well without damage symptoms in a highly acid and a moderately acid soil horizon. The moderately acid A_h+B_w-horizon of a Eutric Cambisol was favourable to seedling growth. The fine root development was reduced in the highly acid A+B_w-horizon of a Dystric Cambisol and in the A_h+E-horizon of a Haplic Podzol, the latter of which also caused increased mortality. Seedling growth in the B₂-horizon of the Haplic Podzol was vigorous, in spite of a higher level of extractable Al and lower base saturation as compared with the A_h+E-horizon. These results are interpreted in relation to soil acidity, soil Al and nutritional status of the seedlings. We conclude that neither Al-toxicity nor nutrient deficiency cause the damage symptoms observed in the A_h+E-horizon of a Haplic Podzol and the fine root reduction in the A+B_w-horizon of a Dystric Cambisol. The damage symptoms of the PZh_A treatment seems to be more the result of H-toxicity or H-related factors other than nutrient shortage or Al-toxicity. Other pH-related toxic factors are discussed.     

Founder effect in a Belgian-Dutch fragile X population

For many years, the high prevalence of the fragile X syndrome was thought to be caused by a high mutation frequency. The recent isolation of the FMR1 gene and identification of the most prevalent mutation enable a more precise study of the fragile X mutation. As the vast majority of fragile X patients show amplification of an unstable trinucleotide repeat, DNA studies can now trace back the origin of the fragile X mutation. To date, de novo mutations leading to amplification of the CGG repeat have not yet been detected. Recently, linkage disequilibrium was found in the Australian and US populations between the fragile X mutation and adjacent polymorphic markers, suggesting a founder effect of the fragile X mutation. We present here a molecular study of Belgian and Dutch fragile X families. No de novo mutations could be found in 54 of these families. Moreover, we found significant (P < 0.0001) linkage disequilibrium in 68 unrelated fragile X patients between the fragile X mutation and an adjacent polymorphic microsatellite at DXS548. This suggests that a founder effect of the fragile X mutation also exists in the Belgian and Dutch populations. Both the absence of new mutations and the presence of linkage disequilibrium suggest that a few ancestral mutations are responsible for most of the patients with fragile X syndrome.     

Penicillin-binding proteins of clostridia

The penicillin-binding protein (PBP) profiles of 33Clostridium perfringens and sixClostridium species isolated from clinically significant infections were analyzed. Three new PBPs—PBPs 2B, 4B, and 5B (84, 70, and 49 kDa respectively)—and a high-molecular-weight PBP 6 (45 kDa) were demonstrated in theC. perfringens isolates. In addition to PBPs 1 and 2, PBPs 2B and 4B were seen to show low binding affinities for penicillin, although further studies are required to determine their possible roles in the development of penicillin resistance. The PBP profiles of theC. perfringens isolates were complex. Variations in apparent molecular weights (M _r s) of all PBPs, with the exception of PBP 5 and the presence or absence of PBPs 2, 3, and 4B, gave rise to nine different PBP patterns. The high-M _rPBPs 5 and 6, which exhibited high-penicillin-binding affinities, were with only one exception consistent within theC. perfringens isolates. These PBPs 5 and 6 of theC. perfringens isolates and independent PBPs found in the otherClostridium species studied indicate that PBP analysis may assist in the differentiation ofClostridium spacies.     

Characterization of a porcine glucosephosphate isomerase-processed pseudogene at Chromosome 1q1.6-1.7

A porcine glucosephosphate isomeraseprocessed pseudogene has been isolated and sequenced. The pseudogene has several base substitutions as well as an insertion and deletions, and is 83% homologous to the corresponding cDNA. It contains an intervening sequence of 565 bp, is truncated at the 3 end, and is flanked by direct repeats of seven nucleotides. Fluorescent in situ hybridization to porcine metaphase chromosomes localized the processed pseudogene to Chromosome (Chr) 1q1.6-1.7. A (GT)₁₄(AT)₁₅ microsatellite was detected close to the processed pseudogene.     

Reflection contrast microscopy of ultrathin sections in immunocytochemical localization studies: a versatile technique bridging electron microscopy with light microscopy

Reflection contrast microscopy (RCM) of ultrathin sections was recently introduced as a sensitive technique for visualization with enhanced definition in immunogold histochemistry. Experience of using RCM as a major tool in immunocytochemical research in different fields is summarized, e.g. oncology, nephrology and embryology. The sensitive visualization of immunocytochemical labels, gold particles or peroxidase-diaminobenzidine deposits in or on ultrathin sections, by RCM instead of electron microscopy is demonstrated. RCM of ultrathin sections is an adequate light microscopical alternative for immunoelectron microscopy, since an overview of both label and tissue is obtained with a high image definition and high contrast of label. In the studies presented, RCM is shown to provide a better gradation in staining intensity and staining pattern than other light microscopical methods. Moreover, a precise localization of multiple labels is obtained with this method. Besides the applications shown, ultrathin section visualization by RCM is very useful for correlative light- and electron microscopical studies of fine structures. Commercially available fluorescence microscopes can be adapted for proper RCM functioning; an adaptation scheme and list of microscopes tested is provided.     

Growth and nutrient dynamics of beech (Fagus sylvatica L.) seedlings in acid soils

The relative uptake rates of N, P, K, S, Ca, Mg, Fe, Mn, Zn, Cu, and Al were estimated in beech seedlings pot cultured in the field in six acid soils (treatments). The relative uptake rates were compared with the relative growth rates. The relative uptake rates of N, K and Ca agreed well with the growth rates of the seedlings irrespective of widely differing soil conditions (acid sand-clayey till, pH 4–6). The relative uptake rates of P, Fe, and Al differed from that predicted by the growth rate. The uptake rates of Fe and Al were highest at the lowest growth rates, and the P uptake rate was lower than the growth rate in these treatments. Thus the P availability probably limited growth in an eluvial (E) horizon of a podzol, and possibly in the illuvial (B) horizon of a podzol and in an acid clayey till (Dystric Cambisol). Low P uptake was associated with a tendency towards higher relative root growth rates. In terms of the concept of steady state nutrition the high relative root growth rate in some treatments may be interpreted as an acclimation to low P supply. The P limitation seemed to be related to interactions among Fe, Al and organic compounds of the soil solution.FAX no: +4646104423     

Nitrogen mineralization in native cultivated and abandoned fields in shortgrass steppe

We conducted a set of in situ incubations to evaluate patterns of N availability among dominant land uses in the shortgrass steppe region of Colorado, USA, and to assess recovery of soil fertility in abandoned fields. Replicated 30 d incubations were performed in 3 sets of native (never cultivated), abandoned (cultivated until 1937), and currently cultivated, fallow fields. Net N mineralization and the percentage of total N that was mineralized increased in the order: native, abandoned, cultivated. Higher soil water content in fallow fields is the most likely reason for greater mineralization in cultivated fields, while higher total organic C and C/N ratios in native and abandoned fields may explain differences in mineralization between these land uses. Recovery of soil organic matter in abandoned fields appears to involve accumulation of soil C and N under perennial plants, but probable methodological artifacts complicate evaluation of the role of individual plants in recovery of N availability. Higher N mineralization and turnover in cultivated fields may make them more susceptible to N losses; recovery of N cycling in abandoned fields appears to involve a return to slower N turnover and tighter N cycling similar to native shortgrass steppe.     

Crystal structure and spin crossover studies on bis(2,6-bis(benzimidazol-2-yl)pyridine) iron(II) perchlorate

The structure of the [Fe(bzimpy)₂](ClO₄)₂·xH₂O system (x = 0.25) was determined by single crystal X-ray structure analysis. The Fe(II) ion is hexacoordinated by six donor nitrogen atoms. The magnetic properties of the complex were investigated by powder magnetic susceptibility measurements and ESR. The freshly prepared sample does not show any traces of iron(III) impurities but these are formed as a function of time. After 1 year the sample contains 8.2% iron(III) as shown by UV spectroscopy and indicated by g_eff = 4.3 and 2.0 in its ESR spectrum. This explains the recorded ξ versus T behaviour at low temperature: with increasing temperature the ξ value decreases according to the Curie-Weiss law for a S = 5/2 system having an effective g = 4.3. Above 220 K a continuous increase in the ξ value is observed and a spin crossover applies. The spin transition is not complete at room temperature. A pronounced hysteresis is observed upon heating/cooling the sample between 220 and 414 K on the basis of magnetic data and infrared spectra.