Above-ground biomass estimation in closed canopy Neotropical forests using lidar remote sensing: factors affecting the generality of relationships

Aim Previous studies have developed strong, site‐specific relationships between canopy metrics from lidar (light detecting and ranging) remote sensing data and forest structural characteristics such as above‐ground biomass (AGBM), but the generality of these relationships is unknown. In this study, we examine the generality of relationships between lidar metrics and forest structural characteristics, including AGBM, from two study areas in Central America with different precipitation patterns. Location A series of tropical moist forest sites in Panama and a tropical wet forest in Costa Rica. Methods Canopy metrics (e.g. canopy height) were calculated from airborne lidar data. Basal area, mean stem diameter and AGBM were calculated from measurements taken as a part of ongoing forest dynamics studies in both areas. We examined the generality of relationship between lidar metrics and forest structure, and possible environmental effects (e.g. leaf phenology). Results We found that lidar metrics were strongly correlated (R²: 0.65–0.92) with mean stem diameter, basal area and AGBM in both regions. We also show that the relationships differed between these regions. Deciduousness of canopy trees in the tropical moist forest area accounted for the differences in predictive equations for stem diameter and basal area. The relationships between lidar metrics and AGBM, however, remained significantly different between the two study areas even after adjusting for leaf drop. We attribute this to significant differences in the underlying allometric relationships between stem diameter and AGBM in tropical wet and moist forests. Conclusions Important forest structural characteristics can be estimated reliably across a variety of conditions sampled in these closed‐canopy tropical forests. Environmental factors such as drought deciduousness have an important influence on these relationships. Future efforts should continue to examine climatic factors that may influence the generality of the relationships between lidar metrics and forest structural characteristics and assess more rigorously the generality of field‐derived allometric relationships.     

Inter-relationship between testicular dysgenesis and Leydig cell function in the masculinization programming window in the rat

The testicular dysgenesis syndrome (TDS) hypothesis proposes that maldevelopment of the testis, irrespective of cause, leads to malfunction of the somatic (Leydig, Sertoli) cells and consequent downstream TDS disorders. Studies in rats exposed in utero to di(n-butyl) phthalate (DBP) have strongly supported the TDS concept, but so far no direct evidence has been produced that links dysgenesis per se to somatic cell dysfunction, in particular to androgen production/action during the ‘masculinization programming window’ (MPW; e15.5–e18.5). Normal reproductive tract development and anogenital distance (AGD) are programmed within the MPW, and TDS disorders arise because of deficiencies in this programming. However, DBP-induced focal testicular dysgenesis (Leydig cell aggregation, ectopic Sertoli cells, malformed seminiferous cords) is not evident until after the MPW. Therefore, we used AGD as a read-out of androgen exposure in the MPW, and investigated if this measure was related to objectively quantified dysgenesis (Leydig cell aggregation) at e21.5 in male fetuses exposed to vehicle, DBP (500 or 750 mg/kg/day) or the synthetic glucocorticoid dexamethasone (Dex; alone or plus DBP-500) from e15.5–e18.5 (MPW), e13.5–e20.5 or e19.5–e20.5 (late window). Dysgenesis was found only in animals exposed to DBP during the MPW, and was negatively correlated (R² = −0.5) with AGD at e21.5 and at postnatal day 8, irrespective of treatment period. Dysgenesis was also negatively correlated (R² = –0.5) with intratesticular testosterone (ITT) at e21.5, but only when treatments in short windows (MPW, late window) were excluded; the same was true for correlation between AGD and ITT. We conclude that AGD, reflecting Leydig cell function solely within the MPW, is strongly related to focal dysgenesis. Our results point to this occurring because of a common early mechanism, targeted by DBP that determines both dysgenesis and early (during the MPW) fetal Leydig cell dysfunction. The findings provide strong validation of the TDS hypothesis.     

Ligase-Defective Bacteriophage T4 I. Effects on Mutation Rates

Temperature-sensitive mutations in bacteriophage T4 gene 30 (polynucleotide ligase) were examined for their effects on spontaneous and proflavine-induced frameshift mutagenesis in the rII and ac (acridine resistance) cistrons. Only small (fourfold or less) effects on mutation rates were observed, even when selection artifacts involving suppression of gene 30 mutations by rII mutations were taken into account. The deoxyribonucleic acid ligase gene of T4 therefore appears to be only a minor determinant of frameshift mutation rates. This result is consistent with the particular nature of frameshift mutagenesis in bacteriophage T4.     

Increased survival in sepsis by in vivo adenovirus-induced expression of IL-10 in dendritic cells

The dendritic cell (DC) is the most potent APC of the immune system, capable of stimulating naive T cells to proliferate and differentiate into effector T cells. Recombinant adenovirus (Adv) readily transduces DCs in vitro allowing directed delivery of transgenes that modify DC function and immune responses. In this study we demonstrate that footpad injection of a recombinant Adv readily targets transduction of myeloid and lymphoid DCs in the draining popliteal lymph node, but not in other lymphoid organs. Popliteal DCs transduced with an empty recombinant Adv undergo maturation, as determined by high MHC class II and CD86 expression. However, transduction with vectors expressing human IL-10 limit DC maturation and associated T cell activation in the draining lymph node. The extent of IL-10 expression is dose dependent; transduction with low particle numbers (10(5)) yields only local expression, while transduction with higher particle numbers (10(7) and 10(10)) leads additionally to IL-10 appearance in the circulation. Furthermore, local DC expression of human IL-10 following in vivo transduction with low particle numbers (10(5)) significantly improves survival following cecal ligation and puncture, suggesting that compartmental modulation of DC function profoundly alters the sepsis-induced immune response.     

Organothallium(III) reagents for modification of biomacromolecules: irreversible labelling of phosphoglycerate kinase from rabbit muscle

Organothallium(III) reagents, by analogy with organomercurials, have been found to rapidly label phosphoglycerate kinase from rabbit muscle. By use of a radio-labelled version of p-methylphenylthallium(III) bis-trifluoroacetate (MPT) the inhibition was shown to be irreversible by the criterion of gel filtration desalting. The rate of labelling was shown to depend on the temperature, enzyme and thallium reagent concentrations, and the presence or absence of the various substrates of the enzyme. The structure and oxidation state of the thallium reagent used affected the extent of modification by the compounds MPT, o-carboxyphenylthallium(III) bis-trifluoroacetate, thallic trifluoroacetate and thallous acetate. A number of pieces of evidence implicate cysteine residues in the labelling, including changes in the free thiol titre of the enzyme on thalliation, model studies on the interaction of thiols (e.g. glutathione) with thallium(III) and thallous materials, the lack of inactivation of phosphoglycerate kinase from yeast (which has only one thiol residue distant from the active site), and the partial restoration of enzymic activity by treatment of thalliated enzyme with sulphydryl reducing agents. Substrate protection studies showed that modification of rabbit muscle phosphoglycerate kinase by MPT was fully prevented by 3-phosphoglycerate and partially by MgATP. The latter protected only against the fast phase of thallic modification, the slower phase being unaffected. The presence of MgADP potentiated the labelling by MPT. No evidence of an MgADP-induced conformational change in the enzyme could be obtained from fluorescence or circular dichroic spectroscopies, although changes of the native spectra were noted on thalliation by MPT alone. The cross-linking potential of these arylthallium(III) reagents is discussed along with conformational changes required to trigger the hinge-movement between the N- and C-domains of the protein.     

Environment,but not migration rate,influences extinction risk in experimental metapopulations

Ecological theory suggests that several demographic factors influence metapopulation extinction risk, including synchrony in population size between subpopulations, metapopulation size and the magnitude of fluctuations in population size. Theoretically, each of these is influenced by the rate of migration between subpopulations. Here we report on an experiment where we manipulated migration rate within metapopulations of the freshwater zooplankton Daphnia magna to examine how migration influenced each of these demographic variables, and subsequent effects on metapopulation extinction. In addition, our experimental procedures introduced unplanned but controlled differences between metapopulations in light intensity, enabling us to examine the relative influences of environmental and demographic factors. We found that increasing migration rate increased subpopulation synchrony. We failed to detect effects of migration on population size and fluctuations in population size at the metapopulation or subpopulation level, however. In contrast, light intensity did not influence synchrony, but was positively correlated with population size and negatively correlated with population fluctuation. Finally, synchrony did not influence time to extinction, while population size and the magnitude of fluctuations did. We conclude that environmental factors had a greater influence on extinction risk than demographic factors, and that metapopulation size and fluctuation were more important to extinction risk than metapopulation synchrony.     

Depalmitoylated Ras traffics to and from the Golgi complex via a nonvesicular pathway

Palmitoylation is postulated to regulate Ras signaling by modulating its intracellular trafficking and membrane microenvironment. The mechanisms by which palmitoylation contributes to these events are poorly understood. Here, we show that dynamic turnover of palmitate regulates the intracellular trafficking of HRas and NRas to and from the Golgi complex by shifting the protein between vesicular and nonvesicular modes of transport. A combination of time-lapse microscopy and photobleaching techniques reveal that in the absence of palmitoylation, GFP-tagged HRas and NRas undergo rapid exchange between the cytosol and ER/Golgi membranes, and that wild-type GFP-HRas and GFP-NRas are recycled to the Golgi complex by a nonvesicular mechanism. Our findings support a model where palmitoylation kinetically traps Ras on membranes, enabling the protein to undergo vesicular transport. We propose that a cycle of depalmitoylation and repalmitoylation regulates the time course and sites of Ras signaling by allowing the protein to be released from the cell surface and rapidly redistributed to intracellular membranes.     

Effect of CO2 on the fermentation capacities of the acetogen Peptostreptococcus productus U-1.

The fermentative capacities of the acetogenic bacterium Peptostreptococcus productus U-1 (ATCC 35244) were examined. Although acetate was formed from all the substrates tested, additional products were produced in response to CO2 limitation. Under CO2-limited conditions, fructose-dependent growth yielded high levels of lactate as a reduced end product; lactate was also produced under CO2-enriched conditions when fructose concentrations were elevated. In the absence of supplemental CO2, xylose-dependent growth yielded lactate and succinate as major reduced end products. Although supplemental CO2 and acetogenesis stimulated cell yields on fructose, xylose-dependent cell yields were decreased in response to CO2 and acetogenesis. In contrast, glycerol-dependent growth yielded high levels of ethanol in the absence of supplemental CO2, and pyruvate was subject to only acetogenic utilization independent of CO2. CO2 pulsing during the growth of CO2-limited fructose cultures stopped lactate synthesis immediately, indicating that CO2-limited cells were nonetheless metabolically poised to respond quickly to exogenous CO2. Resting cells that were cultivated at the expense of fructose without supplemental CO2 readily consumed fructose in the absence of exogenous CO2 and formed only lactate. Although the specific activity of lactate dehydrogenase was not appreciably influenced by supplemental C02 during cultivation, cells cultivated on fructose under CO2-enriched conditions displayed minimal capacities to consume fructose in the absence of exogenous CO2. These results demonstrate that the utilization of alternative fermentations for the conservation of energy and growth of P. productus U-1 is augmented by the relative availability of CO2 and growth substrate.     

Tolerance and metabolic response of acetogenic bacteria toward oxygen

The acetogens Sporomusa silvacetica, Moorella thermoacetica, Clostridium magnum, Acetobacterium woodii, and Thermoanaerobacter kivui (i) grew in both semisolid and liquid cultivation media containing O(2) and (ii) consumed small amounts of O(2). Low concentrations of O(2) caused a lag phase in growth but did not alter the ability of these acetogens to synthesize acetate via the acetyl coenzyme A pathway. Cell extracts of S. silvacetica, M. thermoacetica, and C. magnum contained peroxidase and NADH oxidase activities; catalase and superoxide dismutase activities were not detected.