Cross‐scale controls on carbon emissions from boreal forest megafires

Climate warming and drying is associated with increased wildfire disturbance and the emergence of megafires in North American boreal forests. Changes to the fire regime are expected to strongly increase combustion emissions of carbon (C) which could alter regional C balance and positively feedback to climate warming. In order to accurately estimate C emissions and thereby better predict future climate feedbacks, there is a need to understand the major sources of heterogeneity that impact C emissions at different scales. Here, we examined 211 field plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories (NWT), Canada after an unprecedentedly large area burned in 2014. We assessed both aboveground and soil organic layer (SOL) combustion, with the goal of determining the major drivers in total C emissions, as well as to develop a high spatial resolution model to scale emissions in a relatively understudied region of the boreal forest. On average, 3.35 kg C m^?2 was combusted and almost 90% of this was from SOL combustion. Our results indicate that black spruce stands located at landscape positions with intermediate drainage contribute the most to C emissions. Indices associated with fire weather and date of burn did not impact emissions, which we attribute to the extreme fire weather over a short period of time. Using these results, we estimated a total of 94.3 Tg C emitted from 2.85 Mha of burned area across the entire 2014 NWT fire complex, which offsets almost 50% of mean annual net ecosystem production in terrestrial ecosystems of Canada. Our study also highlights the need for fine‐scale estimates of burned area that represent small water bodies and regionally specific calibrations of combustion that account for spatial heterogeneity in order to accurately model emissions at the continental scale.     

Structural diversity in a conserved cholera toxin epitope involved in ganglioside binding.

Cholera is a widespread disease for which there is no efficient vaccine. A better understanding of the conformational rearrangements at the epitope might be very helpful for the development of a good vaccine. Cholera toxin (CT) as well as the closely related heat-labile toxin from Escherichia coli (LT) are composed of two subunits, A and B, which form an oligomeric assembly AB5. Residues 50-64 on the surface of the B subunits comprise a conserved loop (CTP3), which is involved in saccharide binding to the receptor on epithelial cells. This loop exhibits remarkable conformational plasticity induced by environmental constraints. The crystal structure of this loop is compared in the free and receptor-bound toxins as well as in the crystal and solution structures of a complex with TE33, a monoclonal antibody elicited against CTP3. In the toxins this loop forms an irregular structure connecting a beta-strand to the central alpha-helix. Ser 55 and Gln 56 exhibit considerable conformational variability in the five subunits of the unliganded toxins. Saccharide binding induces a change primarily in Ser 55 and Gln 56 to a conformation identical in all five copies. Thus, saccharide binding confers rigidity upon the loop. The conformation of CTP3 in complex with TE33 is quite different. The amino-terminal part of CTP3 forms a beta-turn that fits snugly into a deep binding pocket on TE33, in both the crystal and NMR-derived solution structure. Only 8 and 12 residues out of 15 are seen in the NMR and crystal structures, respectively. Despite these conformational differences, TE33 is cross-reactive with intact CT, albeit with a thousandfold decrease in affinity. This suggests a different interaction of TE33 with intact CT.     

Temperature and Abscisic Acid Can Be Used to Regulate Survival,Growth, and Differentiation of Cultured Guard Cell Protoplasts of Tree Tobacco

Guard cell protoplasts isolated from leaves of Nicotiana glauca (Graham) were cultured. Conditions were sought that would maximize survival and maintain cells in their differentiated state. Temperature was an important determinant of survival, growth, and differentiation. As temperatures were increased from 24 to 32[deg]C, survival for 1 week in culture increased from approximately 20% to approximately 80% of cells used to initiate cultures. At all of these temperatures, approximately 90% of surviving cells divided to form callus tissue. "Footprint" areas of cells cultured for 1 week at 32[deg]C increased almost 30-fold. Cells cultured for 1 week at 34 to 40[deg]C also survived in high percentages (approximately 80%), but they retained a morphology similar to that of guard cells and they did not divide. Footprint areas of cells cultured for 1 week at 38[deg]C increased 6-fold. Cells cultured at 36 to 40[deg]C in media containing 0.1 or 1.0 [mu]M abscisic acid survived in high percentages and did not divide. At 38[deg]C their footprint areas did not increase, but cells so cultured increased in diameter when treated with fusicoccin. Morphologies and electrophoretic profiles of total sodium dodecyl sulfate-extractable proteins suggest that cells cultured at 38[deg]C in media containing abscisic acid remain differentiated. L-[alpha]-(2-Aminoethoxyvinyl)-glycine reduced survival to <1% at 26 or 32[deg]C but had no effect at 38[deg]C. At lower temperatures, cell growth and survival appear to be ethylene dependent.     

A role for calcium and protein kinase C in agonist-stimulated adhesion of human neutrophils.

Stimulated adherence of human neutrophils to plastic and changes in cytosolic free Ca2+ concn. [( Ca2+]i) were measured in the same cell preparations. [Ca2+]i-activation curves were constructed to compare the relation between [Ca2+]i and adhesion in response to ionomycin and formylmethionyl-leucyl-phenylalanine (FMLP). This showed that FMLP-stimulated adhesion required less increase in [Ca2+]i than did ionomycin's effect, a result suggesting that an additional stimulatory component might be involved in the response to FMLP. Protein kinase C activation was a possibility, and activation of protein kinase C with a phorbol ester (PMA) was found to stimulate adhesion with no change in [Ca2+]i. A low concentration of PMA was found to synergize with ionomycin to stimulate a greater adhesion response than with each alone, and the [Ca2+]i-activation curve for ionomycin in the presence of PMA was shifted towards that for FMLP. Thus, synergy between [Ca2+]i and protein kinase C (each of which is sufficient alone) probably explains the stimulatory effects of FMLP on adhesion of neutrophils.     

Immunological relationships and post-translational modifications of human salivary amylase (Amy1) and pancreatic amylase (Amy2) isozymes

Electrophoretic phenotypes of human salivary amylase (Amy₁) and pancreatic amylase (Amy₂) consist of complex isozyme patterns which may result from post-translational modifications of the primary products of the amylase loci. Biochemical separation of the two molecular weight families of salivary amylase and development of a new electrophoretic system have allowed the identification of complete isozyme patterns corresponding to variant alleles in Amy ₁ and Amy₂ heterozygotes. Further, immunological studies show no nonidentities among salivary isozymes and among pancreatic isozymes, which is to be expected if each series is derived from a single gene product. Both results support the hypothesis that the primary products of the amylase loci undergo post-translational modifications. Salivary and pancreatic amylase appear to be immunologically identical.This investigation was supported in part by PHS Research Grant GM-19178.Supported by PHS Training Grant DE 119.Supported by PHS Training Grant GM 1056.     

Connections between mitochondria and endoplasmic reticulum in rat liver and onion stem

Summary Smooth-surfaced elements of endoplasmic reticulum contact and are attached to the outer membranes of mitochondria in rat liver and onion stem. Some connections appear as short, 150–300 Å diameter tubules that bridge the space between the conjoining elements. In liver, the smooth-surfaced endoplasmic reticulum cisternae connected to the outer mitochondrial membrane are shown to be continuous with rough-surfaced endoplasmic reticulum. Here, the smooth-surfaced endoplasmic reticulum is identified in negatively stained preparations of isolated cell fractions and in thin sections of tissues by the presence of lipoprotein particles characteristic of this cell component. In onion, the identification of endoplasmic reticulum is based on continuity with rough-surfaced endoplasmic reticulum.     

Genetic basis for high limonene—cineole content of exceptional Mentha citrata hybrids

Summary Most Mentha species have 1–25% 1-limonene and 0.5–8% 1,8-cineole, but 19 individuals having more than 50% limonene-cineole were found in a progeny of 10,000 Strain 2 M. citrata — M. crispa F ₁ hybrids. When the same strain of M. citrata (2 n = 96) having the genotype I₁I₁ i ₂ i ₂, a lavender herbage odor with oil assaying 30% linalool and 58.5% linalyl acetate, is hybridized with the closely related octoploid species M. aquatica (2 _n = 96) having the genotype i ₁ i ₁ i ₂ i ₂, a menthofuran herbage odor with oil assaying 65–80% menthofuran, the fertile F ₁ hybrids should have the genotype I ₁ i ₁ i ₂ i ₂ and a lavender odor with oil assaying 84–90% linalool — linalyl acetate. In addition to 111 normal lavender-odored hybrids, this cross gave one individual (Strain 38) having 20.4% limonene and 36.4% cineole and one individual (Strain 625) having 67.5% limonene and 23.6% cineole. Since M. aquatica is homozygous for menthofuran production, and since Strain 38 — M. aquatica backcross progenies had the disomic ratio of 1 limonene and cineole-odored: 1 methofuran-odored, it is evident that the 57% limonene — cineole content of Strain 38 is due to a single dominant gene Lm. Strains 38 and 625 were hybridized with other tester species having known genotypes for other oil constituents to demonstrate that the gene Lm prevents the conversion of limonene to more advanced compounds, namely: carvone, pulegone, methofuran, menthone, menthol, and menthyl acetate which are normally developed in the oil of other species having the recessive gene lm. Strain 38 hybrids with M. citrata show that the dominant I gene interrupts oil biogenesis at an earlier stage than the Lm gene and largely prevents the synthesis of limonene and cineole. Nine of 21 strains having 57– 94% limonene — cineole were investigated. Strains 38 and 62 had the genotype i ₁ i ₁ i _{2 i 2} Lm ₁ lm ₁ lm ₂ lm ₂ or i ₁ i ₁ i ₂ i ₂ lm ₁ lm ₁ Lm ₂ lm ₂, whereas Strain 625 and six others had the genotype i ₁ i ₁ i ₂ i ₂ Lm ₁ lm ₁ Lm ₂ 1m ₂. These segregants from the segmental allopolyploids may be explained by assuming that M. aquatica has the genotype and Strain 2 of M. citrata the genotype with A and a designating the non-homologous centromere regions of the two chromosome pairs carrying the linked genes on different chromosome arms. Crossing over between the genes would not be detectible when there is normal autosyndetic bivalent pairing, whereas occasional quadrivalent pairing of the four chromosomes of Strain 2 of M. citrata could lead to gene interchanges between chromosomes non-homologous for the centromere region.Research Assistant, Research Assistant, Senior Chemist, and Director of Plant Research respectively.     

Chemogenetic evidence supporting multiple allele control of the biosynthesis of (−)-menthone and (+)-isomenthone stereoisomers in Mentha species

The essential oils of certain Mentha species and chemotypes have proportions of (?)-menthone and (+)-isomenthone which differ but show a high degree of heritability in clonal propagation. Oil from an F₂ individual (69–296), selected from numerous 4n M. longifolia (4n = 48) × M. crispa (2n = 48) hybrids for high isomenthone content, had 41.3% isomenthone; the associated but seldom observed alcohols, 1.6% isomenthol, 10.3% neoiso-menthol; and 13% of their esters; in contrast to 8% menthone with 0.1% menthol, 5.0% neo-menthol, and 1.7% esters. Self-pollination of strain 69–296 gave a 3:1 ratio of high isomenthone: high menthone. Crosses with a true breeding high menthone plant having 80% menthone and 3.2% isomenthone gave a 1:1 ratio of the parental phenotypes by GLC analyses and herbage odor. This and data from high isomenthone and high menthone crosses with tester strains lead us to postulate the involvement of a single locus having multiple alleles with true breeding menthone having the genotype P^s P^s, true breeding isomenthone P^r P^r, 69–296 P^r P^s, and high pulegone pp. The P^r allele is not completely dominant over the P^s allele in 69–296 as about 18% of the total ketone derived from pulegone is menthone. Both are dominant over the recessive allele p that largely prevents menthone development. The quantitative amounts of the two isomers are believed to be controlled by the six combinations of the three alleles in a diploid species with graded effects obtained in the more complex genotypes possible in double diploid and octoploid species. 69–296 has (?)-piperitone even though (+)-piperitone is believed to be the common isomer in Mentha.