The impact of boreal forest fire on climate warming.

We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 +/- 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 +/- 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.

Influence of opioid use on surgical and long-term outcome after resection for chronic pancreatitis.

BACKGROUND: The outcome of pancreatic resection for chronic pancreatitis in patients with preoperative opioid use is not well described. METHODS: During 1997 to 2003, 112 of 231 patients referred with chronic pancreatitis underwent pancreatic resection. The outcome of patients who had preoperative opioid use (N=46) was compared with those without (N=66). RESULTS: Patients who used opioids presented at a younger age and had a younger age of symptom onset, longer symptom duration, more hospitalizations, a higher frequency of diabetes mellitus, a higher pain score, and more restriction in daily activity (all P<.05). Twenty-one (46%) patients with opioid use had a total pancreatectomy compared with 9 (14%) without opioid use (P=.0002); the 21 patients also had a higher frequency of postoperative bleeding and early reoperation (8 vs 2, P<.02; 11 vs 3, P=.003, respectively). Mortality and overall morbidity was not significantly different between the 2 groups (4 vs 1, 27 vs 34, respectively). Pain scores improved postoperatively in both groups (P=.001) and was not significantly different between the groups from 12 months onward (median follow-up of 12 months, range, 3-60 months). Twenty percent of patients who used preoperative opioids however reverted to morphine use compared with 6% of patients who had not used opioids. CONCLUSIONS: Patients who used opioids had more advanced disease than patients without opioid use, accounting for part of the postoperative morbidity. Although long-term pain relief was comparable between the 2 groups, maintaining opioid withdrawal was more problematic in those with preoperative opioid use. Earlier referral for resection may be warranted in this group of patients.

fMRI-adaptation reveals dissociable neural representations of identity and expression in face perception.

The distributed model of face processing proposes an anatomical dissociation between brain regions that encode invariant aspects of faces, such as identity, and those that encode changeable aspects of faces, such as expression. We tested for a neuroanatomical dissociation for identity and expression in face perception using a functional MRI (fMRI) adaptation paradigm. Repeating identity across face pairs led to reduced fMRI signal in fusiform cortex and posterior superior temporal sulcus (STS), whereas repeating emotional expression across pairs led to reduced signal in a more anterior region of STS. These results provide neuroanatomical evidence for the distributed model of face processing and highlight a dissociation within right STS between a caudal segment coding identity and a more rostral region coding emotional expression.

Factors controlling long- and short-term sequestration of atmospheric CO2 in a mid-latitude forest.

Net uptake of carbon dioxide (CO2) measured by eddy covariance in a 60- to 80-year-old forest averaged 2.0 +/- 0.4 megagrams of carbon per hectare per year during 1993 to 2000, with interannual variations exceeding 50%. Biometry indicated storage of 1.6 +/- 0.4 megagrams of carbon per hectare per year over 8 years, 60% in live biomass and the balance in coarse woody debris and soils, confirming eddy-covariance results. Weather and seasonal climate (e.g., variations in growing-season length or cloudiness) regulated seasonal and interannual fluctuations of carbon uptake. Legacies of prior disturbance and management, especially stand age and composition, controlled carbon uptake on the decadal time scale, implying that eastern forests could be managed for sequestration of carbon.

Analysis of immune system gene expression in small rheumatoid arthritis biopsies using a combination of subtractive hybridization and high-density cDNA arrays.

Subtractive hybridization of cDNAs generated from synovial RNA which had been isolated from patients with rheumatoid arthritis (RA) or normal controls was used in conjunction with high-density array hybridization to identify genes of immunological interest. The method was designed to detect gene expression in small needle biopsy specimens by means of a prior amplification of nanogram amounts of total RNA to full-length cDNA using PCR. The latter was cut with Rsa I, ligated with adapters, hybridized with unmodified driver cDNA, and subjected to suppression subtraction PCR. Differentially expressed products were cloned into E. coli and picked into 384 well plates. Inserts were obtained by PCR across the multiple cloning site, and the products arrayed at high density on nylon filters. The subtracted cDNAs were also labelled by random priming for use as probes for library screening. The libraries chosen were the subtracted one described above and a set of 45,000 ESTs from the I.M. A.G.E consortium. Clones showing positive hybridization were identified by sequence analysis and homology searching. The results showed that the subtracted hybridization approach could identify many gene fragments expressed at different levels, the most abundant being immunoglobulins and HLA-DR. The expression profile was characteristic of macrophage, B cell and plasma cell infiltration with evidence of interferon induction. In addition, a significant number of sequences without matches in the nucleotide databases were obtained, this demonstrates the utility of the method in finding novel gene fragments for further characterisation as potential members of the immune system. Although RA was studied here, the technology is applicable to any disease process even in cases where amounts of tissue may be limited.

Automated measurements of CO(2) exchange at the moss surface of a black spruce forest.

We used an automated, multiplexing gas-exchange system to measure the net exchange of CO(2) at the surfaces of three shady feather moss and three exposed sphagnum moss sites in a black spruce forest during 35 days at the end of the 1995 growing season. Midday gross photosynthesis was 0.5 to 1.0 micro mol m(-2) s(-1) by feather moss and 0.5 to 2.5 micro mol m(-2) s(-1) by sphagnum moss. Photosynthesis by sphagnum moss was reduced by approximately 70% at 0 degrees C, and reached a maximum rate at 8 degrees C. Nighttime CO(2) efflux, the sum of soil and moss respiration was 1 to 2.5 micro mol m(-2) s(-1) above feather moss and 0.5 to 1.5 micro mol m(-2) s(-1) above sphagnum moss at moss temperatures of 0 to 15 degrees C. The higher rates of respiration at the feather moss sites probably reflected a greater belowground input of carbon from black spruce, and the lower rates of photosynthesis were probably associated with shading by the black spruce canopy. Photosynthesis by moss accounted for 10 to 50% of whole-forest gross CO(2) uptake measured simultaneously by eddy covariance. Respiration at the moss surface was 50 to 90% of whole-forest respiration, with a decreasing fraction on warm nights apparently because of a disproportionate rise in aboveground respiration.

Carbon assimilation and water-use efficiency by neighboring Mediterranean-climate oaks that differ in water access.

Quercus agrifolia Nee and Quercus durata Jeps. are sclerophyllous evergreens that co-occur in regions of northern California that have a serpentine-derived soil. The species are of similar stature and density where they grow together, even though late-drought xylem pressure potentials indicate that Q. durata has access to more soil water than Q. agrifolia. To assess how carbon uptake and water-use efficiency (WUE) are affected by water access, I monitored leaf and canopy gas exchange of neighboring Q. durata and Q. agrifolia trees over a 15-month period. Transpiration and photosynthesis by Q. agrifolia peaked in spring and declined through the summer, whereas transpiration and photosynthesis by Q. durata continued at a moderate rate year round. When summed over the study, Q. agrifolia transpired 25% less water on a ground-area basis than Q. durata, but assimilated 25% more carbon. Quercus agrifolia achieved a greater integrated WUE by: (1) maintaining a 20% advantage in instantaneous WUE as a result of lower leaf intercellular CO(2) concentrations; (2) responding rapidly to increased soil water following rain; and (3) assimilating carbon at high rates during periods of low evaporative demand.

Environmental controls on the photosynthesis and respiration of a boreal lichen woodland: a growing season of whole-ecosystem exchange measurements by eddy correlation.

Measurements of net ecosystem CO2 exchange by eddy correlation, incident photosynthetically active photon flux density (PPFD), soil temperature, air temperature, and air humidity were made in a black spruce (Picea mariana) boreal woodland near Schefferville, Quebec, Canada, from June through August 1990. Nighttime respiration was between 0.5 and 1.5 kg C ha-1 h-1, increasing with temperature. Net uptake of carbon during the day peaked at 3 kg C ha-1 h-1, and the daily net uptake over the experiment was 12 kg C ha-1 day-1. Photosynthesis dropped substantially at leaf-to-air vapor pressure deficit (VPD) greater than 7 mb, presumably as a result of stomatal closure. The response of ecosystem photosynthesis to incident PPFD was markedly non-linear, with an abrupt saturation at 600 µmol m-2 s-1. This sharp saturation reflected the geometry of the spruce canopy (isolated conical crowns), the frequently overcast conditions, and an increase in VPD coincident with high radiation. The ecosystem light-use efficiency increased markedly during overcast periods as a result of a more even distribution of light across the forest surface. A mechanistic model of forest photosynthesis, parameterized with observations of leaf density and nitrogen content from a nearby stand, provided accurate predictions of forest photosynthesis. The observations and model results indicated that ecosystem carbon balance at the site is highly sensitive to temperature, and relatively insensitive to cloudiness.

Diurnal patterns of leaf photosynthesis, conductance and water potential at the top of a lowland rain forest canopy in Cameroon: measurements from the Radeau des Cimes.

Diurnal patterns of leaf conductance, net photosynthesis and water potential of five tree species were measured at the top of the canopy in a tropical lowland rain forest in southwestern Cameroon. Access to the 40 m canopy was by a large canopy-supported raft, the Radeau des Cimes. The measurements were made under ambient conditions, but the raft altered the local energy balance at times, resulting in elevated leaf temperatures. Leaf water potential was equal to or greater than the gravitational potential at 40 m in the early morning, falling to values as low as -3.0 MPa near midday. Net photosynthesis and conductance were typically highest during midmorning, with values of about 10-12 micro mol CO(2) m(-2) s(-1) and 0.2-0.3 mol H(2)O m(-2) s(-1), respectively. Leaf conductance and net photosynthesis commonly declined through midday with occasional recovery late in the day. Photosynthesis was negatively related to leaf temperature above midday air temperature maxima. These patterns were similar to those observed in other seasonally droughted evergreen communities, such as Mediterranean-climate shrubs, and indicate that environmental factors may cause stomatal closure and limit photosynthesis in tropical rain forests during the midday period.

Molecular biology of resistance to potato virus X in potato.

It has been proposed that plants express resistance to pathogens when the product of a resistance gene interacts with an elicitor molecule produced by the pathogen. Although there is one instance with tobacco mosaic virus (TMV) in which virus resistance is known to act through the same type of mechanism, it is not known whether this model accounts generally for resistance interactions with plant viruses. To address this issue the interactions of resistance genes in potato with potato virus X (PVX) have been analysed at the molecular level. PVX is an RNA virus that is affected by three different types of resistance locus in various potato cultivars. By using recombinant isolates of PVX, incorporating components of strains or mutant viruses able to overcome or avoid the effects of the resistance loci, we have identified different regions of the viral genome that determine the outcome of the resistance interaction. This information has allowed us to investigate the resistance in detail. For example, with the resistance specified by the Rx locus, it has been shown that the coat protein is an avirulence determinant and elicitor of an induced resistance. This resistance acts by reducing virus accumulation in the inoculated cell. Although the recognition component of the resistance is highly specific, the induced response is apparently non-specific and is effective against viruses unrelated to PVX in cells doubly inoculated with PVX and a second virus. The recognition function of Rx is also expressed in Gomphrena globosa which is a non-host plant of PVX. Based on these data, we propose that virus resistance fits the paradigm of resistance to fungal and bacterial pathogens and that there are similarities between the mechanism of cultivar specific resistance and non-host resistance to pathogen attack. Further analysis of the mechanism of the non-specific response phase may ultimately allow genetic engineering of broad-spectrum virus resistance in crop plants.

A feature of the coat protein of potato virus X affects both induced virus resistance in potato and viral fitness.

The coat protein of PVX determines whether isolates of PVX are affected by Rx-mediated resistance in potato. Isolates with the coat protein of PVXHB are not affected by the resistance; those with the coat protein of PVXUK3 elicit an extreme resistance in the Rx potato that prevents virus accumulation, even on the inoculated leaf. In this paper we describe the analysis of a series of hybrid and mutant isolates of PVXHB and PVXCP4 which were inoculated to plants and protoplasts of Rx and rx cultivars of potato. From the virulence phenotypes of these isolates we conclude that elicitation of the resistance is affected by amino acids 121 and 127 of the viral coat protein, with codon 121 being the major determinant. PVXHB and hybrid or mutant isolates with lysine and arginine at positions 121 and 127 were able to overcome the resistance of Rx, whereas those with threonine and arginine were resistance sensitive both on plants and in protoplasts. The viral isolates with single mutations at either codon 121 or 127 were less infectious than the wild-type or double mutant isolates although, in protoplasts of the susceptible cultivar of potato, they accumulated as well as the wild-type virus. Taken together these data suggest that amino acids 121 and 127 affect a feature of the viral coat protein which may interact with cellular components involved in the spread of PVX and with the product of the Rx resistance gene.

A Potato Virus X Resistance Gene Mediates an Induced, Nonspecific Resistance in Protoplasts.

The Rx locus in potato controls extreme resistance to most isolates of potato virus X (PVX). The resistance is expressed in whole plants and in protoplasts. Rx-mediated resistance in protoplasts causes reduced accumulation of all PVX RNA species, including the (-) strand RNA after a lag of 8 hr postinoculation. In work reported elsewhere, we have shown that the Rx-breaking property of PVXHB was associated with the coat protein gene of PVXUK3 and PVXCP4. Here, we describe how a frameshift mutation in the coat protein gene had no effect on Rx resistance breaking but compromised the Rx-mediated resistance to PVXCP4. We also describe how in coinoculation experiments, the Rx-mediated resistance could be induced to affect PVXHB or cucumber mosaic virus (CMV). In these experiments, PVXHB or CMV was coinoculated to protoplasts (Rx genotype) together with an isolate of PVX, which is affected by Rx. We interpret this data to indicate that Rx-mediated resistance is induced when the PVX coat protein is produced in the infected cells and that the induced resistance mechanism is effective against viruses unrelated to PVX.

Functionally Homologous Host Components Recognize Potato Virus X in Gomphrena globosa and Potato.

All known isolates of potato virus X (PVX), with the exception of a South American isolate PVXHB, induce an extreme resistance response on potato carrying the Rx gene and elicit the production of necrotic lesions on Gomphrena globosa: PVXHB establishes systemic infection on Rx genotypes of potato and infects the inoculated leaf of G. globosa without lesion formation. Previously, we have shown that the Rx-mediated resistance is affected by a feature of the coat protein that depends on the presence of a threonine residue at position 121 in the coat protein of PVXCP4 and that the resistance is an induced response expressed in protoplasts of potato with the Rx genotype. In this study, we provide evidence, based on the analysis of PVXCP4/PVXHB hybrids, that the elicitation of lesions on G. globosa also requires the presence of a threonine residue at position 121 of the viral coat protein. The lesion-forming phenotype was not associated with the ability of the viral isolate to accumulate in the infected plant. We therefore propose that there is a homologous component of both potato carrying Rx and G. globosa that interacts with a feature of the PVX coat protein and, following the interaction, activates an induced response in the plant cell.

Comparative light and electron microscopic analyses of tenuivirus major noncapsid protein (NCP) inclusion bodies in infected plants, and of the NCP in vitro.

Tenuivirus infections are associated with the formation of abundant inclusion bodies and with the accumulation of large quantities of a viral noncapsid protein (NCP) in infected plants. Examination of maize stripe virus and rice hoja blanca virus-infected plant tissues using light, immunofluorescent, and electron microscopy showed that the inclusion bodies induced by the two viruses were very similar. Light microscopy revealed that both induced arrays of ring-like, figure-eight-like, and amorphous inclusions, frequently with a substructure of needle-shaped crystals. Immunofluorescent staining showed that all types of inclusion bodies contained the viral NCP but not the viral N protein, associated to the viral RNA. Electron microscopy revealed abundant amorphous semi-electron-opaque inclusion bodies; these had a fibrillar appearance but also occurred as compact, more electron-dense structures. Filamentous electron-opaque inclusion bodies were also detected. Immunogold labeling of ultrathin sections confirmed that all inclusion bodies included NCP and that none included viral N protein. Examination of purified NCP showed that it can form similar amorphous and crystalline arrays in vitro to the inclusion bodies observed in vivo. We propose that the common presence of NCP in all inclusion bodies implies the existence of a single type of intracellular inclusion body, the different developmental stages of which have previously been considered to be distinct inclusion bodies.

Net Exchange of CO2 in a Mid-Latitude Forest.

The eddy correlation method was used to measure the net ecosystem exchange of carbon dioxide continuously from April 1990 to December 1991 in a deciduous forest in central Massachusetts. The annual net uptake was 3.7 +/- 0.7 metric tons of carbon per hectare per year. Ecosystem respiration, calculated from the relation between nighttime exchange and soil temperature, was 7.4 metric tons of carbon per hectare per year, implying gross ecosystem production of 11.1 metric tons of carbon per hectare per year. The observed rate of accumulation of carbon reflects recovery from agricultural development in the 1800s. Carbon uptake rates were notably larger than those assumed for temperate forests in global carbon studies. Carbon storage in temperate forests can play an important role in determining future concentrations of atmospheric carbon dioxide.

Structure of tobraviral particles: a model suggested from sequence conservation in tobraviral and tobamoviral coat proteins.

Comparisons of the coat protein sequences of four tobraviruses with those of seven tobamoviruses indicate that these proteins share a common evolutionary origin. Numerous amino acids for which specific functions have been identified in the molecular structure of the tobacco mosaic virus vulgare protein have identical or closely similar counterparts among the tobraviral proteins. These include those with roles in the hydrophobic core of the protein, those that contribute to the RNA binding site and those involved in the control of virus assembly. We suggest a model for the structure of the tobraviral particle that not only offers an explanation for the greater diameter of the tobraviral particle but also confirms an early suggestion for RNA placement within this particle.

Molecular analysis of a resistance-breaking strain of potato virus X.

Full-length cDNA clones of potato virus X (PVX) strains PVXUK3 and PVXHB have been constructed in plasmid vectors to allow in vitro transcription of infectious PVX RNA. In both instances the transcript-derived virus infected tobacco and potato identically to the respective progenitor strains: in tobacco and susceptible potato cultivars both strains infected systemically, producing symptomless or mild mosaic symptoms. In potato carrying the Rx or Nx resistance genes, the virus derived from the PVXHB cDNA infected systemically, whereas the virus derived from the PVXUK3 cDNA failed to infect the Rx plants or induced apical necrosis, characteristic of a hypersensitive response of the Nx gene. Three hybrid viral genomes were constructed at the cDNA level to localize the resistance breaking determinants of PVXHB. Transcripts of all three hybrids were infectious on tobacco. On potato cultivars with either the Rx or Nx resistance genes, the hybrid viruses infected in the same way as PVXHB, rather than PVXUK3. The common feature of these hybrid viruses, the coat protein gene, is therefore the determinant of Nx and Rx resistance breaking of PVXHB.