Soil‐based habitat partitioning in understorey palms in lower montane tropical forests

Aim Dispersal assembly and niche assembly are two competing theories proposed to explain the maintenance of species diversity in tropical forests. Dispersal theory emphasizes the role of chance colonization events and distance‐limited seed dispersal in explaining species abundance and distribution, whereas niche theory emphasizes differences among species in requirements for potentially limiting resources. Species distribution patterns in tropical forests often correlate with geology and topography, but tests of the relative importance of dispersal and niche partitioning have been hampered by an inadequate characterization of resource availability. The aim of this study was to explore how soil chemical and physical properties, climate, and geographic distance affect understorey palm communities in lower montane forests. Location Fortuna Forest Reserve, Chiriqui Province, and Palo Seco Forest Reserve, Bocas del Toro Province, in western Panama. Methods Understorey palms and soil nutrient concentrations were surveyed within 10 sites on different soil types across a 13‐km transect. Variation in palm community composition was examined in relation to spatial and environmental variables. Results The 25 understorey palm species recorded in the study were non‐randomly distributed among forests differing in soil nutrient availability. In support of dispersal theory, floristic similarity decreased predictably with increasing geographic distance. However, environmental and soil variables were also correlated with geographic distance. Floristic similarity was also highly associated with a subset of environmental variables. Variation in palm community similarity was most strongly correlated with inorganic nitrogen availability and cation concentration. A subset of soil variables had a stronger relationship with floristic similarity when geographic distance was controlled for than did geographic distance when differences in soils were controlled for. Main conclusions Both dispersal and niche processes affect palm species distribution patterns. Although spatially limited dispersal may influence species distribution patterns, soil‐based habitat associations, particularly with respect to soil nitrogen, cation availability and aluminium concentrations, remain important factors influencing palm community composition at the mesoscale level in this tropical montane forest.     

Gramicidin channels that have no tryptophan residues.

In order to understand how aromatic residues modulate the function of membrane-spanning proteins, we examined the role of the four tryptophans in gramicidin A (gA) in determining the average duration and permeability characteristics of membrane-spanning gramicidin channels; the tryptophan residues were replaced by tyrosine (gramicidin T, gT), tyrosine O-benzyl ether [gramicidin T(Bzl), gT(Bzl)], naphthylalanine (gramicidin N, gN), and phenylalanine (gramicidin M enantiomer, gM-). These analogues form channels with durations and conductances that differ some 10- and 16-fold, respectively. The single-channel conductance was invariably decreased by the Trp----Yyy replacement, and the relative conductance alterations were similar in phosphatidylcholine (DPhPC) and monoglyceride (GMO) bilayers. The duration variations exhibited a more complex pattern, which was quite different in the two membrane environments: in DPhPC bilayers, gN channels have an average duration that is approximately 2-fold longer than that of gA channels; in GMO bilayers, the average duration of gN channels is about one-tenth that of gA channels. The sequence-dependent alterations in channel function do not result from alterations in the channels' peptide backbone structure, because heterodimers can form between the different analogues and gramicidine A, and there is no energetic cost associated with heterodimer formation [cf. Durkin, J. T., Koeppe, R. E., II, & Andersen, O. S. (1990) J. Mol. Biol. 211, 221]. The alterations in permeability properties are consistent with the notion that Trp residues alter the energy profile for ion permeation through long-range electrostatic interactions.     

Multimodal assessment of pain in the esophagus: a new experimental model

A new multimodal pain assessment model was developed integrating electrical, mechanical, cold, and warmth stimuli into the same device. The device, with a bag and electrodes for electrical stimulation, was positioned in the lower part of the esophagus in 11 healthy subjects. Mechanical stimuli were delivered with an impedance planimetric system. Thermal stimuli were performed by circulating water of different temperatures (5-50 degrees C) inside the bag. All subjects reported both nonpainful and painful local and referred sensations to all stimuli. Temporal summation to repeated electrical stimuli could be studied. For all stimuli, there was a relationship between stimulus intensity and pain intensity. The referred pain area increased with increasing intensity of the electrical and mechanical stimuli. There were several differences between the sensations evoked by the four stimulus modalities, indicating activation of different visceral nerve pathways. This model offers the possibility for controlled multimodal stimuli activating the superficial and deeper layers of the human gut and should be used in basic, clinical, and pharmacological pain studies.     

Characterization of cationic liposomes based on dimethyldioctadecylammonium and synthetic cord factor from M. tuberculosis (trehalose 6,6'-dibehenate)-a novel adjuvant inducing both strong CMI and antibody responses

Incorporation of the glycolipid trehalose 6,6'-dibehenate (TDB) into cationic liposomes composed of the quaternary ammonium compound dimethyldioctadecylammonium (DDA) produce an adjuvant system which induces a powerful cell-mediated immune response and a strong antibody response, desirable for a high number of disease targets. We have used differential scanning calorimetry (DSC) to investigate the effect of TDB on the gel-fluid phase transition of DDA liposomes and to demonstrate that TDB is incorporated into DDA liposome bilayers. Transmission Electron Microscopy (TEM) and cryo-TEM confirmed that liposomes were formed when a lipid film of DDA containing small amounts of TDB was hydrated in an aqueous buffer solution at physiological pH. Furthermore, time development of particle size and zeta potential of DDA liposomes incorporating TDB during storage at 4 degrees C and 25 degrees C, indicates that TDB effectively stabilizes the DDA liposomes. Immunization of mice with the mycobacterial fusion protein Ag85B-ESAT-6 in DDA-TDB liposomes induced a strong, specific Th1 type immune response characterized by substantial production of the interferon-gamma cytokine and high levels of IgG2b isotype antibodies. The lymphocyte subset releasing the interferon-gamma was identified as CD4 T cells.     

The pyridine nucleotide and non-pyridine nucleotide dependence of L-glutamate dehydrogenase in the histochemical system

Summary Under histochemical conditions (fresh frozen sections from liver, kidney and cerebellum of the rat) it was shown that the oxidation of L-glutamic acid was carried out by the NAD-dependent L-glutamate dehydrogenase (E.C. 1.4.1.2) and/or the NAD- or NADP-dependent L-glutamate dehydrogenase (E.C. 1.4.1.3) as well as by an enzyme system which is not dependent on externally added NAD, NADP, FAD, FMN or CoQ₁₀ for activity.This non-pyridine dependent activity was related to the L-glutamate dehydrogenases proper, owing to the following: a) the localization of activity noticed corresponds to that obtained with the NAD- or NADP-containing media, b) the incubation time needed for initial formation of red and blue formazans is similar to that with coenzyme-containing media, c) pre-extraction experiments reveal similarity in enzyme diffusion rates, d) the named activity is influenced by the same agents and to the same extent as the activity obtained by the inclusion of NAD or NADP (e.g. dissociation of the dehydrogenase molecule into subunits due to urea, inhibition of activity due to N-ethyl maleimide and 1.10-phenanthroline, activation due to the allosteric effect of ADP and to high substrate concentration, allosteric inhibition caused by GTP and inhibition caused by -ketoglutaric acid, no inhibitory effect of KCN), and e) the named activity was not affected by added PMS (excluding activity due to L-aminoacid oxidase).In the in situ localization of enzyme activity it was found that L-glutamate dehydrogenases E.C. 1.4.1.2 and E.C. 1.4.1.3 co-exist in the cells of kidney and cerebellum, while the L-glutamate dehydrogenase E.C. 1.4.1.3 only was present in liver cells.Finally, it was stated that incubation time should be kept as short as possible in order to avoid Nothing dehydrogenase reaction as well as inhibition due to accumulation of -ketoglutaric acid. Only gel incubation media should be applied.Recipient of a research grant from the Danish Ministry of Education     

Oxidative and calcium stress regulate DSCR1 (Adapt78/MCIP1) protein

DSCR1 (adapt78) is a stress-inducible gene and cytoprotectant. Its protein product, DSCR1 (Adapt78), also referred to as MCIP1, inhibits intracellular calcineurin, a phosphatase that mediates many cellular responses to calcium. Exposure of human U251 and HeLa cells to hydrogen peroxide led to a rapid hyperphosphorylation of DSCR1 (Adapt78). Inhibitor and agonist studies revealed that a broad range of kinases were not responsible for DSCR1 (Adapt78) hyperphosphorylation, including ERK1/2, although parallel activation of the latter was observed. Phosphorylation of both DSCR1 (Adapt78) and ERK1/2 was attenuated by inhibitors of tyrosine phosphatase, suggesting the common upstream involvement of tyrosine dephosphorylation. The hyperphosphorylation electrophoretic shift in DSCR1 (Adapt78) mobility was also observed with other oxidizing agents (peroxynitrite and menadione) but not nonoxidants. Calcium ionophores strongly induced the levels of both hypo- and hyper-phosphorylated DSCR1 (Adapt78) but did not alter phosphorylation status. Calcium-dependent growth factor- and angiotensin II-stimulation also induced both DSCR1 (Adapt78) species. Phosphorylation of either or both serines in a 13-amino acid peptide made to a calcineurin-interacting conserved region of DSCR1 (Adapt78) attenuated inhibition of calcineurin. These data indicate that DSCR1 (Adapt78) protein is a novel, early stage oxidative stress-activated phosphorylation target and newly identified calcium-inducible protein, and suggest that these response mechanisms may contribute to the known cytoprotective and calcineurin-inhibitory activities of DSCR1 (Adapt78).     

Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm

Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica , exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10-fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid.     

Phase I and II metabolism and carbohydrate metabolism in cultured cryopreserved porcine hepatocytes

Primary porcine hepatocytes were cryopreserved using freezing boxes or a programmable freezer (PF). Upon thawing and culturing in 12-well plates cryopreserved hepatocytes were compared with their fresh controls on days 1 and 2 after plating. Cryopreserved hepatocytes attached approximately as well as fresh hepatocytes and useful cultures were obtained. In cryopreserved hepatocytes, coumarin 7-hydroxylation, 6beta-testosterone hydroxylation and p-nitrophenol glucuronidation were reduced to about 10-40, 35 and 40%, respectively, compared to their fresh counterparts. Glycogen synthesis in cryopreserved hepatocytes was reduced to about 30% on day 1 of culture and about 47% on day 2 of culture compared to the synthesis in fresh hepatocytes. Both fresh and cryopreserved hepatocytes increased the synthesis by twofold in response to stimulation with insulin. Reduced basal levels of glycogen and of glycogen synthesis could be explained by an increased energy demand in cryopreserved hepatocytes needing to repair damages caused by cryopreservation. Glycogenolysis was reduced to about 50% in cryopreserved hepatocytes and gluconeogenesis to about 40% of the glucose production in fresh hepatocytes. In both fresh and cryopreserved hepatocytes the glucose production from glycogenolysis and gluconeogenesis, respectively, was increased fourfold in response to stimulation with glucagon. Overall, the hepatocytes cryopreserved in boxes had a tendency to perform better than hepatocytes cryopreserved in a programmable freezer. In conclusion, the cryopreserved hepatocytes were metabolic active; however, to a lower extent than the fresh hepatocytes, although, the cryopreserved hepatocytes responded as well as the fresh hepatocytes to insulin and glucagon.