Soil 13C–15N dynamics in an N2-fixing clover system under long-term exposure to elevated atmospheric CO2

Reduced soil N availability under elevated CO₂ may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N₂‐fixing system. We studied the effects of Trifolium repens (an N₂‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO₂ under FACE conditions. ¹⁵N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha^?1 yr^?1 and the CO₂ concentration was increased to 60 Pa pCO₂ using ¹³C‐depleted CO₂. The total soil C content was unaffected by elevated CO₂, species and rate of ¹⁵N fertilization. However, under elevated CO₂, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (f_N) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO₂, had a significant effect on f_N values of the total soil N pool. The fractions of newly sequestered C (f_C) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO₂, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more ¹⁵N fertilizer than T. repens: 179 vs. 101 kg N ha^?1 for the low rate of N fertilization and 393 vs. 319 kg N ha^?1 for the high N‐fertilization rate. As the loss of fertilizer‐¹⁵N contributed to the ¹⁵N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N₂ fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N₂‐fixing L. perenne system. This suggests that N₂ fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.     

Systolic Blood Pressure is Related to Catecholamine Sensitivity in Subcutaneous Abdominal Fat Cells

A relationship between abdominal obesity and hypertension is well established. In search for an early-onset defect in adipocyte function linking these two conditions, we compared catecholamine sensitivity in subcutaneous abdominal fat cells with 24-hour systolic, mean arterial and diastolic blood pressure in 16 healthy, normotensive subjects. Clear inter-individual variations in the adipocyte lipolytic adrenoceptor sensitivity (pD₂) for noradrenaline were observed in dose-response experiments (i.e., about 4 log units). An inverse and independent correlation was found between the 24-hour systolic blood pressure and pD₂ for noradrenaline (r = ?0.67, p < 0.01). The mean arterial blood pressure was also negatively correlated to peripheral noradrenaline sensitivity (r = ?0.58, p < 0.05). However, no significant relationship between the 24-hour diastolic blood pressure and pD₂ for noradrenaline was demonstrated. In conclusion we suggest that catecholamine resistance in subcutaneous fat cells may be associated with autonomic dysfunction and impaired blood pressure regulation. This finding is supported by the fact that both noradrenaline sensitivity and 24-hour systolic blood pressure also are correlated to the individual orthostatic heart rate responses, reflecting the sympathetic nervous system tone (r=0.61, p=0.01 and r= ?0.53, p=0.03, respectively). The relationship between noradrenaline sensitivity and systolic blood pressure may be of importance in the early development of hypertension in man.     

Characterization of the activity of fatty-acid epoxide hydrolase in seeds of castor bean (Ricinus communis L.)

Epoxide hydrolase (EC 3.3.2.3) activity was measured with [1-¹⁴C]cis-9,10-epoxystearic acid as the substrate. Homogenates were prepared from the endosperm tissue of germinating seeds of castor bean (Ricinus communis L. zanzibariensis). The activity of fatty-acid epoxide hydrolase was characterized with respect to dependence on time, amount of protein, pH and temperature. Analyses of enzyme distribution in endosperm, cotyledons, root and hypocotyl showed the highest total activity in the endosperm, less in the cotyledons and low activity in the root and hypocotyl. The specific activity was similar for cotyledons and endosperm. Analysis of the temporal expression of the enzyme in the endosperm during germination revealed high activity already in the imbibed seed. Activity was maximal between days four to six and then decreased at the end of one week. Subcellular fractionation of endosperm revealed a dual distribution of activity between the glyoxysomal and the cytosolic fractions.     

A high-resolution map of the vicinity of the R1 locus on chromosome V of potato based on RFLP and AFLP markers

The R1 allele confers on potato a race-specific resistance to Phytophthora infestans. The corresponding genetic locus maps on chromosome V in a region in which several other resistance genes are also located. As part of a strategy for cloning R1, a high-resolution genetic map was constructed for the segment of chromosome V that is bordered by the RFLP loci GP21 and GP179 and includes the R1 locus. Bulked segregant analysis and markers based on amplified fragment length polymorphisms (AFLP markers) were used to select molecular markers closely linked to R1. Twenty-nine of approximately 3200 informative AFLP loci displayed linkage to the R1 locus. Based on the genotypic analysis of 461 gametes, eight loci mapped within the GP21–GP179 interval. Two of those could not be seperated from R1 by recombination. For genotyping large numbers of plants with respect to the flanking markers GP21 and GP179 PCR based assays were also developed which allowed marker-assisted selection of plants with genotypes Rr and rr and of recombinant plants.     

Feeding the fairy shrimp Streptocephalus (Anostraca - Crustacea) with the rotifer Anuraeopsis

Laboratory-cultured Streptocephalus torvicornis were offered 8 concentrations (from 6 to 800 ind. ml^–1) of Anuraeopsis fissa for periods of 2 h 30 min. Two size classes, small (male: 14.7 mm± 1.6, female: 15.4 mm± 1.3) and large (male: 20.0 mm±2.0, female: 23.1 mm± 1.5), of S. torvicornis were used. Functional response for large S. torvicornis (both sexes) plateaued at 400 rotifers ml^–1, while in small specimens it did so at 200 prey ml^–1. Females consumed significantly more (30%) prey than males. Large males consumed maximum 4730 rotifers h^–1, females 6560 h^–1.     

Historical biogeography and morphological differentiation ofStreptocephalus torvicornis (Waga) since the Würm III-glaciation

We argue that the Würm III glaciation eradicated possible European populations ofS. torvicornis, and that today, a reconquest of Europe takes place on two fronts.A western wave has reached the Pyrenees, an eastern one now occupies most of eastern and northern Europe. The western route probably started in the Maghreb, the eastern one in the Levant and the Ponto-Caspian. Animals in the west had to move north by crossing, at right angles, a series of east-west oriented river valleys and progressed slowly; animals in the east could move up river valleys extending north-east, and moved quickly. Italy was not occupied, becauseS.torvicornis is a warm stenotherm, and by the time the climate had warmed sufficiently for it to reach the southern shore of the mediterranean (ca 6000 BP), the gap with Italy was probably too large for a crossing. Cold-loving species (of the generaBranchipus, Chirocephalus) conversely, and could freely flow across the Central Mediterranean at low sea-levels (ca 12000 BP), and now occur in Italy (and the rest of Europe) as well as in Northern Africa.A prediction of our hypothesis is that the pioneer populations in Spain and Central Europe should have been isolated longest. Thisis tested and confirmed by their comparative morphology, and two subspecies,S. t. torvicornis andS. t. bucheti are reinstated.A gap across the Nile Valley where onlyS. rubricaudatus seems to occur, deserves further study.     

High-resolution mapping by YAC fragmentation of a 2.5-Mb Xp22 region containing the human RS, KFSD and CLS disease genes

The disease loci for X-linked Retinoschisis (RS), Keratosis follicularis spinulosa decalvans (KFSD), and Coffin-Lowry syndrome (CLS) have been localized to the same, small region in Xp22 on the human X Chromosome (Chr). To generate a high-resolution map of the available contig in this area, we have used the YAC fragmentation vectors pBP108/ADE2 and pBP109/ADE2 and generated fragmented YACs from a 2.5-Mb YAC (y939H7) spanning the mentioned disease gene candidate regions. Forty-seven fragmented YACs were generated and analyzed, ranging in size from 170 kb to over 2400 kb. The resulting YAC fragmentation panel was used to construct a detailed restriction map of the region and has been used to bin clones and markers. As a deletion panel, it will present a valuable resource for further mapping. Received: 31 December 1996 / Accepted: 22 February 1997     

Somatic expansion of the (CAG) n repeat in Huntington disease brains

The mutation causing Huntington disease (HD) has been identified as an expansion of a polymorphic (CAG) _n repeat in the 5 part of the huntingtin gene. The specific neuropathology of HD, viz. selective neuronal loss in the caudate nucleus and putamen, cannot be explained by the widespread expression of the gene. Since somatic expansion is observed in affected tissue in myotonic dystrophy, we have studied the length of the (CAG) _n repeat in various regions of the brain. Although we have not found clear differences when comparing severely and mildly affected regions, we have observed a minor increase in repeat length upon comparison of affected brain samples with cerebellum or peripheral blood. Hence, although further somatic amplification seems to occur in affected areas of the brain, the differences between affected and unaffected regions are too small to make this mechanism an obvious candidate for the cause of differential neuronal degeneration in HD.     

Two polymorphic dinucleotide repeats in intron 44 of the dystrophin gene

Duchenne muscular dystrophy (DMD) is one of the most common and severe X-linked disorders with an incidence of approximately 1 in 3500 newborn males. In more than 60% of DMD patients, deletions of part or all of the dystrophin gene have been shown. Despite this, carrier detection still poses a problem in some cases, because of the enormous size of the gene and the lack of sufficient numbers of informative markers. Here, we report the isolation and characterization of two additional microsatellite markers (IVS44SK12 and IVS44SK21) in intron 44 of the dystrophin gene. Both markers are useful for carrier detection either by indirect DNA analysis or by direct proof of loss of heterozygosity.