Small-scale dynamics and species richness in successional alvar plant communities

Species richness and small-scale spatial dynamics (turnover) were compared in four sites during 1990-1993 1) former alvar grassland, now young Pinus sylvestris forest, 2) clear-cut in 1990, 3) clear-cut and grazed by sheep, 4) nearby grassland It was hypothesized that in communities which show large-scale dynamics, small-scale dynamics is also more rapid to support succession Area-based species richness and shoot density increased in the cut and grazed site No significant dynamics was found in shoot-based species richness Therefore the forest was considered to be stable and the cut and grazed site large-scale dynamical (successional) Almost equally high small-scale turnover values were found in all sites, which supports the carousel model for successional communities, but means we had to reject the initial hypothesis The successional and intrinsic small-scale dynamics of the communities studied were two separate processes which acted at different scales, but the scale could not be only spatially determined, it depended also on the shoot density The overgrowing of this former alvar grassland has resulted in the decrease of shoot density and thus the decrease of species richness per unit area, but the total number of species has not changed much Consequently the possibility to restore grassland communities remains     

DNA sequences of the two homoeologous SLR1 genes of Brassica napus cv Westar

The DNA sequence data reported have been lodged in the Genbank, EMBL and DDBJ databases under the accession numbers Z21609 and Z26914     

Location of the active site of the bean {alpha}-amylase inhibitor and involvement of a Trp, Arg, Tyr triad

Seeds of the common bean contain three homologous proteins:phytohaemagglutinin E, phytohaemagglutinin L and the lectin-likeprotein     

Human prostatic steroid 5α-reductase isoforms—A comparative study of selective inhibitors

The present study describes the independent expression of the type 1 and 2 isoforms of human 5α-reductase in the baculovirus-directed insect cell expression system and the selectivity of their inhibition. The catalytic properties and kinetic parameters of the recombinant isozymes were consistent with published data. The type 1 isoform displayed a neutral (range 6–8) pH optimum and the type 2 isoform an acidic (5–6) pH optimum. The type 2 isoform had higher affinity for testosterone than did the type 1 isoform (K_m = 0.5 and 2.9 μM, respectively). Finasteride and turosteride were selective inhibitors of the type 2 isoform (K_i (type 2) = 7.3 and 21.7 nM compared to K_i (type 1) = 108 and 330 nM, respectively). 4-MA and the lipido-sterol extract of Serenoa repens (LSESr) markedly inhibited both isozymes (K_i (type 1) = 8.4 nM and 7.2 μg/ml, respectively; K_i (type 2) = 7.4 nM and 4.9 μg/ml, respectively). The three azasteroids were competitive inhibitors vs substrate, whereas LSESr displayed non-competitive inhibition of the type 1 isozyme and uncompetitive inhibition of the type 2 isozyme. These observations suggest that the lipid component of LSESr might be responsible for its inhibitory effect by modulating the membrane environment of 5α-reductase. Partially purified recombinant 5α-reductase type 1 activity was preserved by the presence of lipids indicating that lipids can exert either stimulatory or inhibitory effects on human 5α-reductase.     

Effects of tumour necrosis factor-alpha on BrdU incorporation in cultured human enterocytes

Bromodeoxyuridine incorporation is a useful method for studying the pattern of DNA synthesis in proliferating cells. The distribution pattern of incorporated BrdU in villus enterocytes of duodenal explants was analysed after exposure to TNFalpha in organ culture. TNFalpha caused a consistent, low level uptake of BrdU in the portion of the nucleus close to the nuclear membrane, this pattern was absent from the control cultures. As these epithelial cells are terminally arrested in G(0), the BrdU incorporation was thought not to be due to S phase DNA synthesis, but rather a response to the cytotoxic influence of TNFalpha. Microtitre plate proliferation assays of cell density and DNA synthesis were devised to study the effects of TNFalpha on confluent monolayers of the human foetal jejunal cell line I407 and the mouse fibrosarcoma cell line L929. Both cell lines showed a similar response to TNFalpha. Exposure to TNFalpha alone did not reduce cell numbers but did cause a significant increase in DNA synthesis (p < 0.05). When cycloheximtde was added in tandem with TNFalpha there was a significant reduction in cell number (p < 0.001) and level of DNA synthesis (p < 0.01) indicative of cell death. The DNA of cells exposed to TNFalpha and cycloheximide was fragmented when viewed on an electrophoresis gel. The results show that BrdU incorporation might be a good indicator of damage to the DNA of cells after cytotoxic insult. TNFalpha may be responsible for villus enterocyte damage in enteropathies such as coeliac disease and GVHR of the small bowel.     

The calcium hypothesis of cystic fibrosis

Data have been presented which suggests that various CF cell types show evidence of alterations in calcium homeostasis. The significance of these observations and the exact nature of the putative calcium defect in CF remains to be elucidated. It must also be determined whether this possible defect is primary, or is secondary or tertiary to some more basic lesion. The data reviewed suggests that altered calcium homeostasis may play some focal role in the aetiology or the pathogenesis of CF.     

Studies on regulation of chorionic gonadotropin secretion in primates

The regulation of secretion of chorionic gonadotropin in primates has been studied using bothin vivo andin vitro models.In vivo studies using the pregnant bonnet monkey revealed that at the doses tested, the administration of progesterone or estradiol 17Β in combination or alone did not result in any appreciable change in the duration or magnitude of serum chorionic gonadotropin levels. However, administration of lutropin-releasing hormone by intravenous route resulted in significant increase in chorionic gonadotropin levels within 30–60 min and the extent of stimulation seemed to depend on the state of pregnancy. Forin vitro studies, explants or cells prepared from first trimester human placenta has been used. The functional integrity of these cells has been established by demonstrating the binding of [¹²⁵I]-labelled human chorionic gonadotropin antibody to the cells as well as the synthesis of [³H]-labelled human chorionic gonadotropin.In vitro studies using the cells revealed that addition of lutropin-releasing hormone caused a significant increase in chorionic gonadotropin and estradiol 17Β secreted into the medium. Thus bothin vivo andin vitro results suggest that lutropin-releasing hormone could be one of the factors involved in regulation of chorionic gonadotropin secretion in primates.