Phytogeography of the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica

Aim Central America is a biogeographically interesting area because of its location between the rich and very different biota of North and South America. We aim to assess phytogeographical patterns in the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica. Location Tropical America, in particular the montane area of Cordillera de Talamanca, Costa Rica. Methods The analysis is based on a new critical inventory of the montane bryophyte flora of Cordillera de Talamanca. All species were assigned to phytogeographical elements on the basis of their currently known distribution. Absolute and percentage similarities were employed to evaluate floristic affinities. Results A total of 401 species [191 hepatics (liverworts), one hornwort, 209 mosses] are recorded; of these, 251 species (128 hepatics, one hornwort, 122 mosses) occur in oak forests. Ninety‐three per cent of all oak forest species are tropical in distribution, the remaining 7% are temperate (4%) and cosmopolitan (3%) species. The neotropical element includes almost 74% of the species, the wide tropical element (pantropical, amphi‐atlantic, amphi‐pacific) only 19%. A significant part of the neotropical species from oak forests are species with tropical Andean‐centred ranges (27%). As compared with bryophyte species, vascular plant genera in the study region are represented by fewer neotropical, more temperate and more amphi‐pacific taxa. Bryophyte floras of different microhabitats within the oak forest and epiphytic bryophyte floras on Quercus copeyensis in primary, early secondary and late secondary oak forest show a similar phytogeographical make‐up to the total oak forest bryophyte flora. Comparison of oak forest and páramo reveals a greater affinity of the páramo bryophyte flora to temperate regions and the great importance of the páramo element in páramo. Surprisingly, oak forests have more Central American endemics than páramo. Main conclusions (1) Providing first insights into the phytogeographical patterns of the bryophyte flora of oak forests and páramo, we are able to confirm general phytogeographical trends recorded from vascular plant genera of the study area although the latter were more rich in temperate taxa. (2) Andean‐centred species are a conspicuous element in the bryophyte flora of Cordillera de Talamanca, reflecting the close historical connection between the montane bryophyte floras of Costa Rica and South America. (3) High percentages of Central American endemics in the bryophyte flora of the oak forests suggest the importance of climatic changes associated with Pleistocene glaciations for allopatric speciation.     

Neuronal origin of a cerebral amyloid: neurofibrillary tangles of Alzheimer''s disease contain the same protein as the amyloid of plaque cores and blood vessels.

The protein component of Alzheimer's disease amyloid [neurofibrillary tangles (NFT), amyloid plaque core and congophilic angiopathy] is an aggregated polypeptide with a subunit mass of 4 kd (the A4 monomer). Based on the degree of N-terminal heterogeneity, the amyloid is first deposited in the neuron, and later in the extracellular space. Using antisera raised against synthetic peptides, we show that the N terminus of A4 (residues 1-11) contains an epitope for neurofibrillary tangles, and the inner region of the molecule (residues 11-23) contains an epitope for plaque cores and vascular amyloid. The non-protein component of the amyloid (aluminum silicate) may form the basis for the deposition or amplification (possible self-replication) of the aggregated amyloid protein. The amyloid of Alzheimer's disease is similar in subunit size, composition but not sequence to the scrapie-associated fibril and its constituent polypeptides. The sequence and composition of NFT are not homologous to those of any of the known components of normal neurofilaments.     

Purification and characterization of succinyl-CoA: tetrahydrodipicolinate N-succinyltransferase from Escherichia coli

Tetrahydrodipicolinate succinylase, an enzyme involved in the diaminopimelate-lysine pathway, was purified 1900-fold from crude extracts of Escherichia coli. The enzyme catalyzes the formation of CoA and N-succinyl-2-amino-6-keto-L-pimelate from succinyl-CoA and tetrahydrodipicolinate. The purified enzyme was shown to be homogeneous by polyacrylamide gel electrophoresis. The Stokes radius of the enzyme was determined from its elution volume on a Sephacryl S300 column and its sedimentation constant from sucrose density gradient centrifugation. These were 35 A and 4.7 (S20,w), respectively. The enzyme consists of two subunits each with a mass of 31,000 daltons, as determined using sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Tetrahydrodipicolinate succinylase was shown to be a sulfhydryl enzyme. It has a pH optimum of 8.2. The equilibrium lies predominantly in favor of product formation but the reverse reaction can be demonstrated in vitro.     

Retinoic acid modulates the pattern of cell division in embryos ofLymnaea stagnalis (Mollusca)

All-trans retinoic acid is well known as a modulator of positional specification in vertebrate development. A similar mechanism may operate in molluscan development. Molluscan development is characterized by an invariant pattern of cell divisions, which allows the study of individual cells in the developing organism. Low concentrations of exogenous retinoic acid applied during gastrulation affect the cell division pattern in the early larval stage of the molluscLymnaea stagnalis. A few cells from the apical plate, a larval organ consisting of seven large cleavage-arrested cells, were induced by retinoic acid to resume cell division. They typically formed an area of proliferating small cells that resembles the adjacent areas of precursor cells of adult ectoderm. The identification of individual cells that are transformed by retinoic acid may provide new insights into the mechanisms underlying positional specification within the embryo.     

Occurrence of ornithine decarboxylase and polyamines in cartilage.

The activity of ornithine decarboxylase was investigated in cartilage from chick embryos, rabbits, rats and human foetuses. The enzyme activity in these cartilages was of the same order as the detected in other body tissues. Ornithine decarboxylase activity in chick-embryo cartilage and liver was the same when compared on the basis of total soluble tissue protein. The cartilage enzyme exhibited a pH optimum of 6.5 and a Km for ornithine of 0.16mM. Ornithine decarboxylase activity in chick-embryo pelvic leaflets was maintained at the value in vivo for up to 22h when the isolated tissue was incubated in a modified Waymouth's medium (MB 752/1) at 37 degrees C. After addition of cycloheximide to the incubation medium, ornithine decarboxylase activity declined, with a half-life of 40 min. The concentrations of the polyamines spermidine and spermine in chick-embryo pelvic cartilage and rabbit costal cartilage were of the same order as the concentrations detected in other tissues.     

The effects of IL-1, IL-2, and tumor necrosis factor on polymorphonuclear leukocyte Fc gamma receptor-mediated phagocytosis. IL-2 down-regulates the effect of tumor necrosis factor

It has been reported that the Fc gamma R-mediated phagocytic activity of polymorphonuclear leukocytes (PMN) from patients with acute bacterial infections is markedly enhanced when compared with healthy controls. Inasmuch as several potent cytokines are known to be involved in inflammatory and infectious processes, we studied the effects of three such cytokines (IL-1 beta, IL-2, and TNF-alpha) on normal PMN Fc gamma R-mediated phagocytosis. IL-1 beta and TNF alpha both caused a significant increase in the ingestion of EIgG by adherent PMN. In combination, IL-1 beta and TNF-alpha had an additive effect, even when each was used at its optimal concentration. In contrast to the enhancing effects mediated by IL-1 beta and TNF-alpha, IL-2 alone had no significant effect on PMN phagocytosis. Notably, however, IL-2 at a concentration of 10(4) U/ml partially inhibited TNF-alpha-mediated enhancement of phagocytosis by decreasing TNF binding to the PMN cell surface. This inhibitory effect of IL-2 on TNF was reversed by anti-IL-2 antibody and mAb directed against the low affinity IL-2R (anti-Tac), whereas mAb directed against the intermediate affinity receptor (mik-beta 1) had no such effect. These findings may have important physiologic implications, because patients receiving IL-2 therapy have been shown to have increased susceptibility to infection.     

Xylose anaerobic conversion by open-mixed cultures

Xylose is, after glucose, the dominant sugar in agricultural wastes. In anaerobic environments, carbohydrates are converted into volatile fatty acids and alcohols. These can be used as building blocks in biotechnological or chemical processes, e.g., to produce bioplastics. In this study, xylose fermentation by mixed microbial cultures was investigated and compared with glucose under the same conditions. The product spectrum obtained with both substrates was comparable. It was observed that, in the case of xylose, a higher fraction of the carbon was converted into catabolic products (butyrate, acetate, and ethanol) and the biomass yield was approximately 20% lower than on glucose, 0.16 versus 0.21 Cmol X/Cmol S. This lower yield is likely related to the need of an extra ATP during xylose uptake. When submitted to a pulse of glucose, the population cultivated on xylose could instantaneously convert the glucose. No substrate preference was observed when glucose and xylose were fed simultaneously to the continuously operated bioreactor.