Publications
| Title | Abstract | Year(sorted ascending) Filter | PMID Filter |
|---|
| inhibition of hypoxylon pruinatum by pyrocatechol isolated from bark of aspen. | pyrocatechol has been identified as one of two main substances isolated from bark of aspen (populus tremuloides michx.) which inhibited hypoxylon pruinatum (klot.) cke. total inhibition of this fungus was obtained at a dosage of 640 parts per million. tests with bark extract from two localities showed that inhibition was maximal in samples obtained in the dormant season and from the base of the trees. | 1962 | 14449615 |
| xylem sap flow as affected by metabolic inhibitors and girdling. | the flow of sap in populus tremuloides was studied by the thermoelectric method immediately prior to and at several periods of time after radical girdling. similarly, the flow of sap in betula papyrifera was studied before and after girdling or injection with metabolic inhibitors or a filtrate of a culture of ceratocystis ulmi.none of the treatments caused any significant change in the speed at which the sap flowed. however, the rate at which the temperature rose at the upper (downstream) thermo ... | 1966 | 16656300 |
| plantlets from aspen tissue cultures. | after 2 weeks in the dark, leafy shoots were initiated on subcultured callus tissue of triploid quaking aspen on wolter's medium without auxin and with 6-benzylaminopurine at 0.05, 0.10., 0.15, or 0.20 milligram per liter substituted for kinetin. shoots transferred to wolter's medium under light (323 milliphots) grew large roots and were isolated as plantlets. | 1968 | 5648261 |
| physiological characteristics of photosynthesis and respiration in stems of populus tremuloides michx. | the physiological responses of 6- to 8-year-old aspen (populus tremuloides michx.) stems to temperature, light, and co(2) concentration were investigated in the field throughout the year using infrared co(2) analysis. light response studies showed that the rate of gross photosynthesis was linear from 0 to 400 ft-c (0 to 1.6 mw/cm(2) of 400-700 nm) with light saturation being reached between 800 to 1400 ft-c (3.2 to 5.6 mw/cm(2) of 400-700 nm). at this light intensity, the respiratory co(2) loss ... | 1976 | 16659628 |
| diurnal and seasonal patterns of photosynthesis and respiration by stems of populus tremuloides michx. | the photosynthetic and respiratory rates of 5- to 7-year-old aspen stems (populus tremuloides michx.) were monitored in the field for 1 year to determine the seasonal patterns. the stem was not capable of net photosynthesis, but the respiratory co(2) loss from the stem was reduced by 0 to 100% depending on the time of year and the level of illumination as a result of bark photosynthesis. the monthly dark respiratory rate ranged from 0.24 mg co(2)/dm(2). hr in january to a maximum 7.4 mg co(2)/dm ... | 1976 | 16659737 |
| tree host range and world distribution of the extomycorrhizal fungus pisolithus tinctorius. | the natural occurrence of pisolithus tinctorius has been confirmed in 33 countries of the world and in 38 states in the united states. this ectomycorrhizal fungus is found associated with various tree species in nurseries, urban areas, orchards, forests, and strip-mined spoils. experiments have proved that this fungal symbiont forms ectomycorrhizae with abies procera, betula pendula, carya illnoensis, 11 species of eucalyptus, 30 species of pinus, pseudotsuga menziesii var. meniziesii, 2 species ... | 1977 | 856419 |
| the theory of tree bole and branch form. | working from the general postulate that natural selection of plant form operates so as to maximize the survival potential of a species, this paper examines the hypothesis that the mechanical support of tree foliage must approach optimality in the use of wood, i.e., that tree stems and branches will have "optimal form" with respect to the amount of support tissue. mathematical models of bole and branch form are presented, based on the proposition that either wind or gravity are the primary limiti ... | 1978 | 724980 |
| stomatal conductance and sulfur uptake of five clones of populus tremuloides exposed to sulfur dioxide. | plants of five clones of populus tremuloides michx. were exposed to 0, 0.2 or 0.5 microliter per liter so(2) for 8 hours in controlled environment chambers. in the absence of the pollutant, two pollution-resistant clones maintained consistently lower daytime diffusive conductance (ldc) than did a highly susceptible clone or two moderately resistant clones. differences in ldc among the latter three clones were not significant. at 0.2 microliter per liter so(2), ldc decreased in the susceptible cl ... | 1981 | 16661807 |
| an examination of the leaf quaking adaptation and stomatal distribution in populus tremuloides michx. | the leaves of quaking aspen (populus tremuloides michx.) have a flattened petiole that allows them to quake (oscillate and roll) under low wind velocities. it was hypothesized that this adaptation might enable the plant to respond to windy conditions that would increase transpirational losses. no effects of wind with or without leaf quaking on stomatal resistance were observed under controlled conditions in the field. if wind and leaf quaking affect stomatal resistance, such effects must be smal ... | 1981 | 16661848 |
| photosynthesis and respiration of developing populus tremuloides internodes. | the photosynthetic and respiratory performance of developing internodes of populus tremuloides was evaluated by infrared gas analysis. anatomical and morphological transitions were related to metabolic activity. photosynthetic rates ranged from 6.0 to 10.0 milligrams co(2) per decimeter squared per hour in the youngest internodes to 2.5 to 3.8 milligrams co(2) per decimeter squared per hour in internodes with fully developed bark tissues. respiration exceeded the rate of photosynthesis on the av ... | 1982 | 16662318 |
| leaf conductance as a function of photosynthetic photon flux density and absolute humidity difference from leaf to air. | for an entire season of stomatal activity, leaf or needle conductance was observed on four species, each in a different genus: engelmann spruce (picea engelmannii parry ex engelm.), subalpine fir (abies lasiocarpa [hook.] nutt.), lodgepole pine (pinus contorta var. latifolia engelm.), and aspen (populus tremuloides michx.). conductance in the natural environment was described for all species by photosynthetic photon flux density (ppfd) and absolute humidity difference from leaf to air (dah), as ... | 1982 | 16662336 |
| evaluation of season, temperature, and water stress effects on stomata using a leaf conductance model. | a model was developed earlier describing conductance for three conifers (picea engelmannii parry ex engelm., abies lasiocarpa [hook.] nutt., and pinus contorta var. latifolia engelm.) and one hardwood (populus tremuloides michx.) using only two terms, photosynthetic photon flux density (ppfd) and absolute humidity difference from leaf to air (dah). using residual analysis techniques (actual minus estimated conductance), it was determined that no seasonal or temperature effects existed that were ... | 1982 | 16662337 |
| leaf conductance during the final season of a senescing aspen branch. | leaf conductance, transpiration, and environmental conditions were measured on two aspen (populus tremuloides michx.) branches in a natural stand, using an automatic cuvette system. fortuitously, leaves on one branch senesced about 10 days early, allowing comparison between a senescing branch and a normal branch. terminal bud development was retarded on the senescent branch, and a portion of the branch eventually abscised about 20 centimeters from the end. roughly 1% to 2% of the other branches ... | 1982 | 16662551 |
| persistence of fenitrothion insecticide in poplar populus tremuloides and gray birch betula populifolia. | 1985 | 4052649 | |
| biological delignification of aspen wood by solid-state fermentation with the white-rot fungus merulius tremellosus. | solid-state fermentation of aspen (populus tremuloides) wood with merulius tremellosus for 8 weeks removed 52% of the lignin but only 12% of the total wood weight, and increased the cellulase digestibility to 53% from 18%. water-soluble and enzyme-solubilized lignin degradation products accumulated. delignification was fastest at temperatures between 25 and 32.5 degrees c and at a water-to-wood ratio of 2. initial ph values between 4 and 6 were optimal; m. tremellosus acidified the wood to below ... | 1985 | 16346831 |
| effects of carbon dioxide enrichment and nitrogen supply on growth of boreal tree seedlings. | the effects of two levels of atmospheric carbon dioxide (350 microl l(-1), 750 microl l(-1)) and three levels of nitrogen (15.5 mm, 1.55 mm, 0.155 mm n) on biomass accumulation and partitioning were examined in aspen (populus tremuloides michx.) and white spruce (picea glauca (moench) voss) seedlings grown in controlled environment rooms for 100 days after germination. nitrogen supply had pronounced effects on biomass accumulation, height, and leaf area of both species. root weight ratio (rwr) o ... | 1986 | 14975856 |
| ribulose-1,5-bisphosphate carboxylase activity of populus tremuloides michx. bark tissues. | ribulose-1,5-bisphosphate (rubp) carboxylase was isolated from bark tissue of populus tremuloides michx. by a one-step sephadex g l00-120 column chromatography procedure. the peak fraction had specific activity of 1.3 micromol co(2) mg(-1) chlorophyll min(-1). the bark rubp carboxylase activity was comparable to that of leaf tissues. thus, young corticular tissues are photosynthetically competent and contain sufficient rubp carboxylase to account for the reported rates of photosynthesis. | 1986 | 14975907 |
| organosolv pretreatment for enzymatic hydrolysis of poplars: i. enzyme hydrolysis of cellulosic residues. | aspen (populus tremuloides) and black cottonwood (populus trichocarpa) organosolv pulps produced in a wide range of solvent composition (between 30 and 70% by volume of methanol) and catalysts (h(2)so(4) and h(3)po(4)) such that the cooking liquor ph </= 3 are easily digested by enzymes. the total yields of hydrolysis residues (pulps) are in the 40-60% range; the acid-catalyzed delignification followed by enzyme hydrolysis can generate 70-88% of the original six-carbon sugars contained in the wo ... | 1988 | 18584659 |
| comparative water relations of three successional hardwood species in central wisconsin. | water relations of co-occurring understory saplings of quercus ellipsoidalis e.j. hill, an early successional, xeric species, populus tremuloides michx., an early successional, mesic species, and acer rubrum l., a late successional species that occurs on both wet and dry sites, were evaluated on four dates during the 1986 growing season. the understory was characterized by high soil water content, low irradiance and low vapor pressure deficit throughout the growing season. stomatal conductance a ... | 1988 | 14972816 |
| growth and premature leaf fall in american aspen as bioindications for ozone. | several clones of the american aspen (populus tremuloides michx.) differing in ozone sensitivity were fumigated continuously for 105 days with different ozone concentrations, producing different ozone doses. the suitability of the clones as possible replacements for tobacco as bioindicators in forested areas was tested. the life span of leaves of the ozone-sensitive clones was distinctly reduced by ozone. the difference to controls was significant even in the relatively clean air at birmensdorf. ... | 1988 | 15092605 |
| isoprene emission from aspen leaves : influence of environment and relation to photosynthesis and photorespiration. | isoprene emission rates from quaking aspen (populus tremuloides michx.) leaves were measured simultaneously with photosynthesis rate, stomatal conductance, and intercellular co(2) partial pressure. isoprene emission required the presence of co(2) or o(2), but not both. the light response of isoprene emission rate paralleled that of photosynthesis. isoprene emission was inhibited by decreasing ambient o(2) from 21% to 2%, only when there was oxygen insensitive photosynthesis. mannose (10 millimol ... | 1989 | 16666747 |
| contemporary use of bark for medicine by two salishan native elders of southeast vancouver island, canada. | elders of the saanich and cowichan coast salish people of southern vancouver island treat, or have treated in the recent past, many ailments with bark preparations. interviews with two elder salishan women revealed that: respiratory ailments were treated with bark of abies grandis, arbutus menziesii, cornus nuttallii, prunus emarginata, pseudotsuga menziesii and quercus garryana; digestive tract ailments with the bark of abies grandis, alnus rubra, arbutus menziesii, malus fusca. oemleria cerasi ... | 1990 | 2345461 |
| cdna cloning, sequence analysis and seasonal expression of lignin-bispecific caffeic acid/5-hydroxyferulic acid o-methyltransferase of aspen. | a cdna clone (ptomt 1) encoding a lignin-bispecific o-methyltransferase (omt) was isolated by immunological screening of a lambda gt11 expression library prepared from mrna of developing secondary xylem of aspen (populus tremuloides). nucleotide sequence analysis of ptomt1 revealed an open reading frame of 1095 bp which encodes a polypeptide with a predicted molecular weight of 39,802, corresponding well with the size of the omt polypeptide estimated by sds-page. authenticity of ptomt1 was demon ... | 1991 | 1932694 |
| enzymatic synthesis of isoprene from dimethylallyl diphosphate in aspen leaf extracts. | aspen (populus tremuloides michx.) leaf extracts contain a newly discovered enzyme activity that catalyzes the magnesium ion-dependent elimination of diphosphate from dimethylallyl diphosphate with rearrangement to form isoprene (2-methyl, 1-3-butadiene). this isoprene synthase activity has been partially purified. the nonenzymatic reaction of dimethylallyl diphosphate to isoprene, known to be acid catalyzed, may be insignificant at physiological ph. in contrast, the enzymatic reaction may be re ... | 1991 | 16668590 |
| clonal variation of populus tremuloides responses to diurnal drought stress. | we have developed an automated microprocessor controlled system for subjecting hydroponically grown plants to drought. pumps and valves were used to move nutrient solutions into and out of a system of culture vessels in a growth chamber to provide periods of drought. drought conditions were obtained by exposing the roots of hydroponically grown clones of aspen, populus tremuloides michx., to air in culture vessels temporarily emptied of nutrient medium. over a 3-week period, the daily duration o ... | 1991 | 14972880 |
| carbon dioxide enrichment accelerates the decline in nutrient status and relative growth rate of populus tremuloides michx. seedlings. | changes in growth dynamics and mineral nutrient concentrations were measured in populus tremuloides michx., trembling aspen, grown for 100 days following germination in atmospheres containing 350 or 750 microl l(-1) co(2). seedlings were fertilized with nitrogen (n) at concentrations of 15.5 mm (high-n), 1.55 mm (medium-n), or 0.155 mm (low-n). initially, relative growth rates were enhanced by co(2) enrichment in each n regime, but the effects did not persist. in plants grown in high-n or medium ... | 1991 | 14972887 |
| xylem embolism in response to freeze-thaw cycles and water stress in ring-porous, diffuse-porous, and conifer species. | vulnerability to xylem embolism by freeze-thaw cycles and water stress was quantified in ring-porous (quercus gambelii nutt.), diffuse-porous (populus tremuloides michx., betula occidentalis hook.), and conifer species (abies lasiocarpa nutt., juniperus scopulorum sarg.). embolism was measured by its reduction of xylem hydraulic conductivity; it was induced by xylem tension (water-stress response) and by a tension plus a freeze-thaw cycle (freeze response). conifers showed little (juniperus) or ... | 1992 | 16653035 |
| relationships among isoprene emission rate, photosynthesis, and isoprene synthase activity as influenced by temperature. | isoprene emissions from the leaves of velvet bean (mucuna pruriens l. var utilis) plants exhibited temperature response patterns that were dependent on the plant's growth temperature. plants grown in a warm regimen (34/28 degrees c, day/night) exhibited a temperature optimum for emissions of 45 degrees c, whereas those grown in a cooler regimen (26/20 degrees c, day/night) exhibited an optimum of 40 degrees c. several previous studies have provided evidence of a linkage between isoprene emission ... | 1992 | 16668743 |
| characterization of bispecific caffeic acid/5-hydroxyferulic acid o-methyltransferase from aspen. | bispecific o-methyltransferase (omt, ec 2.1.1.68) which catalyses the meta-specific methylation of caffeic acid and 5-hydroxyferulic acid was purified to homogeneity from the developing secondary xylem of aspen (populus tremuloides). the enzyme was purified by conventional techniques and affinity chromatography on s-adenosyl-l-homocysteine agarose using substrate elution. the enzyme has a m(r) of 40,000 as determined by sds-page. amino acid sequences of three peptides produced from a proteolytic ... | 1992 | 1368360 |
| a novel metabolic pathway for indole-3-acetic acid in apical shoots of populus tremula (l.) x populus tremuloides (michx.). | metabolism of indole-3-acetic acid (iaa) in apical shoots of populus tremula (l.) x populus tremuloides (michx.) was investigated by feeding a mixture of [12c]iaa, [13c6]iaa, and [1[prime]-14c]iaa through the base of the excised stem. hplc of methanolic plant extracts revealed eight major radiolabeled metabolites after a 24-h incubation period. comparison between feeds with [5-3h]iaa and [1[prime]-14c]iaa showed that all detectable metabolites were nondecarboxylative products. the purified radio ... | 1994 | 12232425 |
| cdna and derived amino acid sequence of the chloroplastic copper/zinc-superoxide dismutase from aspen (populus tremuloides). | 1994 | 7824654 | |
| nucleotide divergence between populations of trembling aspen (populus tremuloides) estimated with rapds. | in the present study, a total of 142 trees sampled from five populations of trembling aspen (populus tremuloides michx.) in alberta was analyzed by the polymerase chain reaction (pcr) with five random oligonucleotide primers. null-allele frequencies of 28 putative rapd loci were estimated using the given departure from hardy-weinberg equilibrium (f1s) previously estimated with isozyme markers for the same population. nucleotide divergence between populations was then estimated in a fashion simil ... | 1994 | 7882434 |
| rapd variation within and among natural populations of trembling aspen (populus tremuloides michx.) from alberta. | this article described the population structure of trembling aspen (populus tremuloides michx.) in alberta, a dioecious tree with continuous and wide distribution, and with a primary mode of reproduction through suckering. we studied random amplified polymorphic dna (rapd) variation in 249 trees from eight natural populations. trees within a population were a minimum of 200 m apart to decrease the risk of sampling ramets of a single ortet. of a total of 28 amplified rapd products (bands) from fi ... | 1995 | 8568211 |
| characterization of aspen isoprene synthase, an enzyme responsible for leaf isoprene emission to the atmosphere. | isoprene (2-methyl-1,3-butadiene) is a volatile hydrocarbon emitted from many plant species to the atmosphere, where it plays an important role in atmospheric chemistry. an enzyme extracted from aspen (populus tremuloides) leaves was previously found to catalyze the mg(2+)-dependent elimination of pyrophosphate from dimethylallyl diphosphate (dmapp) to form isoprene (silver, g. m., and fall, r. (1991) plant physiol. 97, 1588-1591). this enzyme, isoprene synthase, has now been purified 4000-fold ... | 1995 | 7768893 |
| nucleotide sequence of a populus tremuloides gene encoding bispecific caffeic acid/5-hydroxyferulic acid o-methyltransferase. | 1995 | 7770534 | |
| photosynthetic productivity of aspen clones varying in sensitivity to tropospheric ozone. | rooted cuttings from three aspen (populus tremuloides michx.) clones (216, 271 and 259, classified as high, intermediate and low in o(3) tolerance, respectively) were exposed to either diurnal o(3) profiles simulating those of michigan's lower peninsula (episodic treatments), or diurnal square-wave o(3) treatments in open-top chambers in northern michigan, usa. ozone was dispensed in chambers ventilated with charcoal-filtered (cf) air. in addition, seedlings were compared to rooted cuttings in t ... | 1995 | 14965916 |
| carbon allocation and partitioning in aspen clones varying in sensitivity to tropospheric ozone. | clones of aspen (populus tremuloides michx.) were identified that differ in biomass production in response to o(3) exposure. (14)carbon tracer studies were used to determine if the differences in biomass response were linked to shifts in carbon allocation and carbon partitioning patterns. rooted cuttings from three aspen clones (216, o(3) tolerant; 271, intermediate; and 259, o(3) sensitive) were exposed to either charcoal-filtered air (cf) or an episodic, two-times-ambient o(3) profile (2x) in ... | 1995 | 14965917 |
| changes in respiration and chemical content during autumnal senescence of populus tremuloides and quercus rubra leaves. | changes in respiration rate, chemical content and chemical concentration were measured in leaves of field-grown populus tremuloides michx. and quercus rubra l. trees throughout the growing season and autumnal senescence. chlorophyll, soluble sugar, n, p, k and mg contents and concentrations all declined during leaf senescence, whereas ca content and concentration increased. leaf dry mass per area declined 24 and 35% in p. tremuloides and q. rubra, respectively, during senescence. in leaves of bo ... | 1995 | 14965995 |
| altered growth and wood characteristics in transgenic hybrid aspen expressing agrobacterium tumefaciens t-dna indoleacetic acid-biosynthetic genes. | a key regulator of cambial growth is the plant hormone indoleacetic acid (iaa). here we report on altered wood characteristics and growth patterns in transgenic hybrid aspen (populus tremula l. x populus tremuloides michx.) expressing agrobacterium tumefaciens t-dna iaa-biosynthetic iaam and iaah genes. eighteen lines simultaneously expressing both genes were regenerated. of these, four lines, verified to be transgenic by northern blot analysis, were selected and raised under controlled growth c ... | 1995 | 12228661 |
| root growth and physiology of potted and field-grown trembling aspen exposed to tropospheric ozone. | we studied root growth and respiration of potted plants and field-grown aspen trees (populus tremuloides michx.) exposed to ambient or twice-ambient ozone. root dry weight of potted plants decreased up to 45% after 12 weeks of ozone treatment, and root system respiration decreased by 27%. the ozone-induced decrease in root system respiration of potted plants was more closely correlated with decreased root dry weight than with specific root respiration, suggesting that aspen root metabolism was l ... | 1996 | 14871758 |
| expression of the agrobacterium rhizogenes rolc gene in a deciduous forest tree alters growth and development and leads to stem fasciation. | we have altered the growth and development of a deciduous forest tree by transforming hybrid aspen (populus tremula x populus tremuloides) with the agrobacterium rhizogenes rolc gene expressed under the strong cauliflower mosaic virus 35s promoter. we demonstrate that the genetically manipulated perennial plants, after a period of dormancy, maintain the induced phenotypical changes during the second growing period. furthermore, mass-spectrometrical quantifications of the free and conjugated form ... | 1996 | 12226405 |
| carrier herbal medicine: traditional and contemporary plant use. | the carrier, an athapaskan-speaking people of northcentral british columbia, occupy the sub-boreal spruce forests of the central interior. this report, which is based on field study, documents some traditional and contemporary knowledge of the medicinal use of plants by the carrier people. important medicinal plants include: abies lasiocarpa, alnus incana, arctostaphylos uva-ursi, artemisia frigida, fragaria virginiana, juniperus communis, picea glauca, pinus contorta, populus tremuloides, rubus ... | 1996 | 8735452 |
| a radial concentration gradient of indole-3-acetic acid is related to secondary xylem development in hybrid aspen. | the radial distribution pattern of indole-3-acetic acid (iaa) was determined across the developing tissues of the cambial region in the stem of hybrid aspen (populus tremula l. x populus tremuloides michx). iaa content was measured in consecutive tangential cryo-sections using a microscale mass spectrometry technique. analysis was performed with wild-type and transgenic trees with an ectopic expression of agrobacterium tumefaciens iaa-biosynthetic genes. in all tested trees iaa was distributed a ... | 1997 | 12223825 |
| sap flow in trembling aspen: implications for stomatal responses to vapor pressure deficit. | we monitored sap flow and estimated diurnal changes in transpiration rates of two trembling aspen (populus tremuloides michx.) stands, located in the southern boreal forest and aspen parkland of saskatchewan, canada. in both stands during the peak growing season (june and july), sap flow during the day (0700-1700 h local time) increased linearly with vapor pressure deficit (vpd) from 0 to about 1 kpa, but then remained remarkably constant at vpd > 1 kpa (up to 4.8 kpa in the aspen parkland stand ... | 1997 | 14759823 |
| regulation of branch-level gas exchange of boreal trees: roles of shoot water potential and vapor pressure difference. | effects of shoot water potential (psi) and leaf-to-atmosphere vapor pressure difference (vpd) on gas exchange of jack pine (pinus banksiana lamb.), black spruce (picea mariana (mill.) b.s.p.), and aspen (populus tremuloides michx.) were investigated at the northern edge of the boreal forest in manitoba, canada. laboratory measurements on cut branches showed that net photosynthesis (a(n)) and mesophyll conductance (g(m)) of jack pine and g(m) of black spruce did not respond to psi until a thresho ... | 1997 | 14759825 |
| growth and maintenance respiration rates of aspen, black spruce and jack pine stems at northern and southern boreas sites. | we measured stem respiration rates during and after the 1994 growing season of three common boreal tree species at sites near the northern and southern boundaries of the closed-canopy boreal forest in central canada. the growth respiration coefficient (r(g); carbon efflux per micro mole of carbon incorporated in structural matter) varied between 0.25 and 0.76, and was greatest for black spruce (picea mariana (mill.) b.s.p.), least for jack pine (pinus banksiana lamb.) and intermediate for trembl ... | 1997 | 14759827 |
| seasonal photosynthetic responses to light and temperature in white spruce (picea glauca) seedlings planted under an aspen (populus tremuloides) canopy and in the open. | photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (picea glauca (moench.) voss) grown for two years in the understory of aspen (populus tremuloides michx.) or in the open in central alberta. light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark resp ... | 1997 | 14759835 |
| vertical gradients in photosynthetic gas exchange characteristics and refixation of respired co(2) within boreal forest canopies. | we compared vertical gradients in leaf gas exchange, co(2) concentrations, and refixation of respired co(2) in stands of populus tremuloides michx., pinus banksiana lamb. and picea mariana (mill.) b.s.p. at the northern and southern boundaries of the central canadian boreal forest. midsummer gas exchange rates in populus tremuloides were over twice those of the two conifer species, and pinus banksiana rates were greater than picea mariana rates. gas exchange differences among the species were at ... | 1997 | 14759908 |
| developmental factors responsible for heterosis in aspen hybrids (populus tremuloides x p. tremula. | juvenile growth and bud set phenology were analyzed to study the biological basis of heterosis (hybrid vigor) in interspecific hybrids of populus tremuloides michx. (t) and p. tremula l. (ta). growth, measured as seedling volume index, was significantly higher for each of the two reciprocal interspecific crosses, t x ta and ta x t, than for the t x t intraspecific cross. broad-sense heritabilities were 2-6 times larger than narrow-sense heritabilities for growth and shoot components in the t x t ... | 1998 | 12651296 |
| seedlings of five boreal tree species differ in acclimation of net photosynthesis to elevated co(2) and temperature. | biochemical models of photosynthesis suggest that rising temperatures will increase rates of net carbon dioxide assimilation and enhance plant responses to increasing atmospheric concentrations of co(2). we tested this hypothesis by evaluating acclimation and ontogenetic drift in net photosynthesis in seedlings of five boreal tree species grown at 370 and 580 &mgr;mol mol(-1) co(2) in combination with day/night temperatures of 18/12, 21/15, 24/18, 27/21, and 30/24 degrees c. leaf-area-based rate ... | 1998 | 12651406 |
| compartmentalized expression of two structurally and functionally distinct 4-coumarate:coa ligase genes in aspen (populus tremuloides). | 4-coumarate:coa ligases (4cls, ec 6.2.1.12) are a group of enzymes necessary for maintaining a continuous metabolic flux for the biosynthesis of plant phenylpropanoids, such as lignin and flavonoids, that are essential to the survival of plants. so far, various biochemical and molecular studies of plant 4cls seem to suggest that 4cl isoforms in plants are functionally indistinguishable in mediating the biosynthesis of these phenolics. however, we have discovered two functionally and structurally ... | 1998 | 9560289 |
| suppression of o-methyltransferase gene by homologous sense transgene in quaking aspen causes red-brown wood phenotypes | homologous sense suppression of a gene encoding lignin pathway caffeic acid o-methyltransferase (caomt) in the xylem of quaking aspen (populus tremuloides michx.) resulted in transgenic plants exhibiting novel phenotypes with either mottled or complete red-brown coloration in their woody stems. these phenotypes appeared in all independent transgenic lines regenerated with a sense caomt construct but were absent from all plants produced with antisense caomt. the caomt sense transgene expression w ... | 1998 | 9576779 |
| host preferences and temporal trends of the tick ixodes angustus in north-central alberta. | we examined host preferences and temporal trends of the tick ixodes angustus on small mammals in north-central alberta. small mammals were live-trapped from 1 june to 29 september 1994 and 3 may to 30 june 1995 in mature aspen (populus tremuloides) forest near lac la biche, alberta. abundance of female i. angustus was high in early may (0.90 +/- 0.20 [se]) and peaked again in late june (0.58 +/- 0.16), whereas abundance of immature i. angustus peaked (1.2 +/- 0.35) in mid-july. red-backed voles ... | 1998 | 9794628 |
| thermotolerance of leaf discs from four isoprene-emitting species is not enhanced by exposure to exogenous isoprene | the effects of exogenously supplied isoprene on chlorophyll fluorescence characteristics were examined in leaf discs of four isoprene-emitting plant species, kudzu (pueraria lobata [willd.] ohwi.), velvet bean (mucuna sp.), quaking aspen (populus tremuloides michx.), and pussy willow (salix discolor muhl). isoprene, supplied to the leaves at either 18 &mgr;l l-1 in compressed air or 21 &mgr;l l-1 in n2, had no effect on the temperature at which minimal fluorescence exhibited an upward inflection ... | 1999 | 10398717 |
| repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees. | because lignin limits the use of wood for fiber, chemical, and energy production, strategies for its downregulation are of considerable interest. we have produced transgenic aspen (populus tremuloides michx.) trees in which expression of a lignin biosynthetic pathway gene pt4cl1 encoding 4-coumarate:coenzyme a ligase (4cl) has been downregulated by antisense inhibition. trees with suppressed pt4cl1 expression exhibited up to a 45% reduction of lignin, but this was compensated for by a 15% increa ... | 1999 | 10429249 |
| genotypic variation for condensed tannin production in trembling aspen (populus tremuloides, salicaceae) under elevated co(2) and in high- and low-fertility soil. | the carbon/nutrient balance hypothesis suggests that leaf carbon to nitrogen ratios influence the synthesis of secondary compounds such as condensed tannins. we studied the effects of rising atmospheric carbon dioxide on carbon to nitrogen ratios and tannin production. six genotypes of populus tremuloides were grown under elevated and ambient co(2) partial pressure and high- and low-fertility soil in field open-top chambers in northern lower michigan, usa. during the second year of exposure, lea ... | 1999 | 10449395 |
| mercuric chloride effects on root water transport in aspen seedlings. | hgcl(2) (0.1 mm) reduced pressure-induced water flux and root hydraulic conductivity in the roots of 1-year-old aspen (populus tremuloides michx.) seedlings by about 50%. the inhibition was reversed with 50 mm mercaptoethanol. mercurial treatment reduced the activation energy of water transport in the roots from 10.82 +/- 0.700 kcal mol(-1) to 6.67 +/- 0.193 kcal mol(-1) when measured over the 4 degrees c to 25 degrees c temperature range. an increase in rhodamine b concentration in the xylem sa ... | 1999 | 10557243 |
| root water flow and growth of aspen (populus tremuloides) at low root temperatures. | effects of root zone temperature on growth, shoot water relations, and root water flow were studied in 1-year-old aspen (populus tremuloides michx.) seedlings. seedlings were grown in solution culture and exposed to day/night air temperatures of 22/16 degrees c and solution culture temperatures of 5, 10, or 20 degrees c for 28 days after bud flush. compared with root growth at 20 degrees c, root growth was completely inhibited at 5 degrees c and inhibited by 97% at 10 degrees c. the 5 and 10 deg ... | 1999 | 10562405 |
| genetic variation in postfire aspen seedlings in yellowstone national park | a rare episode of regeneration of aspen (populus tremuloides michx.) by seeds occurred in yellowstone national park (ynp), wyoming, usa, following extensive fires that occurred in 1988. in 1997, we sampled 410 aspen seedlings from 23 local populations distributed widely across ynp to determine how genetic diversity varies with elevation, substrate, plant competition, ungulate browsing, and geographical location. we employed 132 randomly amplified polymorphic dna (rapd) markers based on six prime ... | 1999 | 10620221 |
| characterization of radiation regimes in nonrandom forest canopies: theory, measurements, and a simplified modeling approach. | we used field measurements and monte carlo simulations of canopy gap-size distribution and gap fraction to examine how beam radiation interacts with clumped boreal forest canopies of aspen (populus tremuloides michx.), black spruce (picea mariana (mill.) b.s.p.) and jack pine (pinus banksiana lamb.). we demonstrate that the beer-lambert law can be modified to accommodate transmission of radiation through a clumped forest canopy as a function of path length or sun zenith angle. multiband vegetati ... | 1999 | 12651308 |
| kinetics of nitrogen uptake by populus tremuloides in relation to atmospheric co(2) and soil nitrogen availability. | sustained increases in plant production in response to elevated atmospheric carbon dioxide (co(2)) concentration may be constrained by the availability of soil nitrogen (n). however, it is possible that plants will respond to n limitation at elevated co(2) concentration by increasing the specific n uptake capacity of their roots. to explore this possibility, we examined the kinetics of (15)nh(4) (+) and (15)no(3) (-) uptake by excised roots of populus tremuloides michx. grown in ambient and twic ... | 2000 | 12651463 |
| responses of trembling aspen and hazelnut to vapor pressure deficit in a boreal deciduous forest. | the branch bag method was used to monitor photosynthesis and transpiration of trembling aspen (populus tremuloides michx.) and hazelnut (corylus cornuta marsh.) over a 42-day midsummer period in 1996, as part of the boreal ecosystem-atmosphere study (boreas). during the same period, daytime measurements of stomatal conductance (g(s)) and leaf water potential (psi(leaf)) were made on these species, and sap flow was monitored in aspen stems by the heat pulse method. weather conditions during the s ... | 2000 | 12651508 |
| isoprene emission inventory for the boreas southern study area. | an isoprene emission inventory for a section of boreal forest in central saskatchewan was developed based on measured emission rates from the two dominant isoprene-emitting species, black spruce (picea mariana (mill.) bsp) and aspen (populus tremuloides michx.). the micrometeorological gradient technique was used to determine isoprene emission factors for establishing the inventory. isoprene fluxes were measured during each of the three boreas intensive field campaigns (ifcs) during the 1994 gro ... | 2000 | 12651509 |
| 5-hydroxyconiferyl aldehyde modulates enzymatic methylation for syringyl monolignol formation, a new view of monolignol biosynthesis in angiosperms. | s-adenosyl-l-methionine-dependent caffeate o-methyltransferase (comt, ec 2.1.1.6) has traditionally been thought to catalyze the methylation of caffeate and 5- hydroxyferulate for the biosynthesis of syringyl monolignol, a lignin constituent of angiosperm wood that enables efficient lignin degradation for cellulose production. however, recent recognition that coniferyl aldehyde prevents 5-hydroxyferulate biosynthesis in lignifying tissue, and that the hydroxylated form of coniferyl aldehyde, 5-h ... | 2000 | 10692459 |
| microsatellite dna markers in populus tremuloides. | markers for eight new microsatellite dna or simple sequence repeat (ssr) loci were developed and characterized in trembling aspen (populus tremuloides) from a partial genomic library. informativeness of these microsatellite dna markers was examined by determining polymorphisms in 38 p. tremuloides individuals. inheritance of selected markers was tested in progenies of controlled crosses. six characterized ssr loci were of dinucleotide repeats (two perfect and four imperfect), and one each of tri ... | 2000 | 10791817 |
| cambial-region-specific expression of the agrobacterium iaa genes in transgenic aspen visualized by a linked uida reporter gene. | the level of indole-3-acetic acid (iaa) was locally modified in cambial tissues of transgenic aspen (populus tremula l. x populus tremuloides michx.). we also demonstrate the use of a linked reporter gene to visualize the expression of the iaa genes. the rate-limiting bacterial iaa-biosynthetic gene iaam and the reporter gene for beta-glucuronidase (gus), uida, were each fused to the cambial-region-specific agrobacterium rhizogenes rolc promoter and linked on the same t-dna. in situ hybridizatio ... | 2000 | 10859183 |
| a xylem-specific cellulose synthase gene from aspen (populus tremuloides) is responsive to mechanical stress. | angiosperm trees accumulate an elevated amount of highly crystalline cellulose with a concomitant decrease in lignin in the cell walls of tension-stressed tissues. to investigate the molecular basis of this tree stress response, we cloned a full-length cellulose synthase (ptcesa) cdna from developing xylem of aspen (populus tremuloides). about 90% sequence similarity was found between the predicted ptcesa and cotton ghcesa proteins. northern blot and in situ hybridization analyses of ptcesa gene ... | 2000 | 10886769 |
| radial distribution pattern of pectin methylesterases across the cambial region of hybrid aspen at activity and dormancy. | biochemical microanalysis combined with tangential cryosectioning was used to visualize the distribution of pectin methylesterases (pmes) across the cambial region in active and dormant hybrid aspen (populus tremula l. x populus tremuloides michx). these novel techniques allowed us to relate activity and isoforms of pmes to specific tissues and developmental stages of the stem to get more information on the physiological function of pmes in cambial growth. isoelectrofocusing analysis revealed nu ... | 2000 | 10982434 |
| spring phenology trends in alberta, canada: links to ocean temperature. | warmer winter and spring temperatures have been noted over the last century in western canada. earlier spring plant development in recent decades has been reported for europe, but not for north america. the first-bloom dates for edmonton, alberta, were extracted from four historical data sets, and a spring flowering index showed progressively earlier development. for populus tremuloides, a linear trend shows a 26-day shift to earlier blooming over the last century. the spring flowering index cor ... | 2000 | 10993558 |
| genotypic variation in physiological and growth responses of populus tremuloides to elevated atmospheric co2 concentration. | physiological and biomass responses of six genotypes of populus tremuloides michx., grown in ambient t (357 micromol mol(-1)) or twice ambient (707 micromol mol(-1)) co2 concentration ([co2]) and in low-n or high-n soils, were studied in 1995 and 1996 in northern lower michigan, usa. there was a significant co2 x genotype interaction in photosynthetic responses. net co2 assimilation (a) was significantly enhanced by elevated [co2] for five genotypes in high-n soil and for four genotypes in low-n ... | 2000 | 11305456 |
| rapid quantification of proanthocyanidins (condensed tannins) with a continuous flow analyzer. | proanthocyanidins (condensed tannins) frequently need to be quantified in large numbers of samples in food, plant, and environmental studies. an automated colorimetric method to quantify proanthocyanidins with sulfuric acid (h(2)so(4)) was therefore developed for use in a continuous flow analyzer. assay conditions were optimized using 50% methanol extracts of paper birch, sugar maple, and quaking aspen leaves. short extraction times and centrifugation of samples prevented proanthocyanidin degrad ... | 2001 | 11368578 |
| ascobotryozyma americana gen. nov. et sp. nov. and its anamorph botryozyma americana, an unusual yeast from the surface of nematodes. | a new teleomorphic genus ascohotryozyma, with a single species, a. americana, is proposed. its anamorph is a botryozyma that differs from the type species, b. nematodophila, on distributional, physiological, and molecular criteria; it is described as botryozyma americana, anam. sp. nov. ascobotryozyma is characterized by globose asci bearing four lunate ascospores. fusion of thallus cells precedes ascus formation. ascobotryozyma americana was isolated from the surface of nematodes (panagrellus d ... | 2001 | 11392486 |
| hydraulic conductance in aspen (populus tremuloides) seedlings exposed to low root temperatures. | low root temperatures significantly reduced root hydraulic conductivity and increased resistance to water flow through the roots of aspen (populus tremuloides michx.) seedlings. increased resistance to water flow could not be fully explained by the corresponding increase in water viscosity at low temperatures. the shapes of arrhenius plots of root water flow and the activation energies were dependent on the direction, sequence and extent of temperature change. the arrhenius plots suggested that ... | 2001 | 11446998 |
| food processing by animals: do beavers leach tree bark to improve palatability? | beavers store and consume tree parts in the bodies of water where they live. we examined whether such soaking renders food more palatable by leaching out undesirable compounds. in experiment 1, saplings of red maple, acer rubrum (rm), were first soaked in a pond for periods of 2, 18, and 36 days, then offered to free-ranging beavers. soaking for two days rendered rm slightly more acceptable to beavers. to further examine the time window around two days, rm sticks were soaked in distilled water i ... | 2001 | 11471937 |
| polyphenol oxidase and herbivore defense in trembling aspen (populus tremuloides): cdna cloning, expression, and potential substrates. | the biochemical anti-herbivore defense of trembling aspen (populus tremuloides michx.) was investigated in a molecular analysis of polyphenol oxidase (ppo; ec 1.10.3.2). a ppo cdna was isolated from a trembling aspen wounded leaf cdna library and its nucleotide sequence determined. southern analysis indicated the presence of two ppo genes in the trembling aspen genome. expression of ppo was found to be induced after herbivory by forest tent caterpillar, by wounding, and by methyl jasmonate treat ... | 2001 | 11473716 |
| gas chromatography-mass spectrometry method for the simultaneous determination of wood extractive compounds in quaking aspen. | we have developed a rapid gas chromatography-mass spectrometry (gc-ms) method for the detailed compositional analysis of 70 underivatized wood extractive components present in quaking aspen (populus tremuloides michx.). forty-four compounds were unequivocally identified by retention time and mass spectral comparison with standards. an additional 26 chromatographic peaks were assigned to broad chemical classes using retention time and mass spectra features. the results were compared to the respec ... | 2001 | 11486867 |
| a kunitz trypsin inhibitor gene family from trembling aspen (populus tremuloides michx.): cloning, functional expression, and induction by wounding and herbivory. | three kunitz trypsin inhibitor genes were isolated from trembling aspen (populus tremuloides) by pcr and cdna screening. based on sequence similarity, they were grouped into two classes. southern blots showed complex banding patterns and a high level of restriction fragment polymorphism between different aspen genotypes, suggesting that these trypsin inhibitors are members of a large, rapidly evolving gene family. one of the trypsin inhibitor genes, ptti2. was over-expressed in escherichia coli ... | 2001 | 11488481 |
| photosynthesis and light-use efficiency by plants in a canadian boreal forest ecosystem. | measurements of the photosynthetic response to midsummer irradiance were made for 11 species representing the dominant trees, understory shrubs, herbaceous plants and moss species in an old black spruce (picea mariana (mill.) b.s.p.) boreal forest ecosystem. maximum rates of photosynthesis per unit foliage area at saturating irradiance, a(max), were highest for aspen (populus tremuloides michx.), reaching 16 micromol m(-2) s(-1). for tamarack (larix laricina (du roi) k. kock) and p. mariana, ama ... | 2001 | 11498339 |
| effects of genotype, nutrient availability, and defoliation on aspen phytochemistry and insect performance. | genetic and environmental variability, and their interactions, influence phytochemical composition and, in turn, herbivore performance. we evaluated the independent and interactive effects of plant genotype, nutrient availability, and defoliation on the foliar chemistry of quaking aspen (populus tremuloides) and consequences for performance of gypsy moths (lymantria dispar). saplings of four genotypes were grown under two conditions of nutrient availability and subjected to three levels of artif ... | 2001 | 11504029 |
| genotypic variation in growth and physiological responses of finnish hybrid aspen (populus tremuloides x p. tremula) to elevated tropospheric ozone concentration. | saplings of six finnish hybrid aspen (populus tremuloides michx. x p. tremula l.) clones were exposed to 0, 50, 100 and 150 ppb ozone (o3) for 32 days in a chamber experiment to determine differences in o3 sensitivity among genotypes. based on the chamber experiment, three clones with intermediate sensitivity to o3 were selected for a free-air o3 enrichment experiment in which plants were exposed for 2 months to either ambient air (control) or air containing 1.3 x the ambient o3 concentration. w ... | 2001 | 11600339 |
| root water flow and leaf stomatal conductance in aspen (populus tremuloides) seedlings treated with abscisic acid. | exogenous abscisic acid (aba) applied to the roots and excised shoots of aspen (populus tremuloides michx.) inhibited stomatal conductance. however, the effect of aba on stomatal conductance was more pronounced in the excised shoots compared with the intact seedlings. approximately 10% of the aba concentration applied to the roots was found in the xylem exudates of root systems exposed to a hydrostatic pressure of 0.3 mpa. a similar concentration of aba applied to the excised shoots produced a f ... | 2001 | 11678278 |
| variation in the susceptibility of the forest tent caterpillar (lepidoptera: lasiocampidae) to bacillus thuringiensis variety kurstaki hd-1: effect of the host plant. | host-mediated effect on the efficacy of bacillus thuringiensis berliner against larvae of the forest tent caterpillar. malacosoma disstria hübner, was investigated under controlled conditions. host plants used in this study were quaking aspen, populus tremuloides michx., a preferred host, and sugar maple, acer saccharum marsh., a secondary host. larvae were reared in the laboratory on leaves of these hosts, and upon reaching the third, fourth, and fifth instar, they were fed leaves treated with ... | 2001 | 11681676 |
| perception of aspen and sun/shade sugar maple leaf soluble extracts by larvae of malacosoma disstria. | we investigated the behavioral feeding preference and the chemoreception of leaf polar extracts from trembling aspen, populus tremuloides, and from sun and shade sugar maple, acer saccharum, by larvae of the polyphagous forest tent caterpillar, malacosoma disstria, a defoliator of deciduous forests in the northern hemisphere. three polar extracts were obtained from each tree species: a total extract, a water fraction, and a methanol fraction. m. disstria larvae were allowed ad libitum access to ... | 2001 | 11710605 |
| growth responses of populus tremuloides clones to interacting elevated carbon dioxide and tropospheric ozone. | the intergovernmental panel of climate change (ipcc) has concluded that the greenhouse gases carbon dioxide (co2) and tropospheric ozone (o3) are increasing concomitantly globally. little is known about the effect of these interacting gases on growth, survival, and productivity of forest ecosystems. in this study we assess the effects of three successive years of exposure to combinations of elevated co2 and o3 on growth responses in a five trembling aspen (populus tremuloides) clonal mixture in ... | 2001 | 11789918 |
| consequences of elevated carbon dioxide and ozone for foliar chemical composition and dynamics in trembling aspen (populus tremuloides) and paper birch (betula papyrifera). | atmospheric chemical composition affects foliar chemical composition, which in turn influences the dynamics of both herbivory and decomposition in ecosystems. we assessed the independent and interactive effects of co2 and o3 fumigation on foliar chemistry of quaking aspen (populus tremuloides) and paper birch (betula papyrifera) at a free-air co2 enrichment (face) facility in northern wisconsin. leaf samples were collected at five time periods during a single growing season, and analyzed for nit ... | 2001 | 11789920 |
| impacts of elevated co2 and/or o3 on leaf ultrastructure of aspen (populus tremuloides) and birch (betula papyrifera) in the aspen face experiment. | impacts of elevated atmospheric o3 and/or co2 on three clones of aspen (populus tremuloides michx.) and birch (betula papyrifera marsh.) were studied to determine, whether or not elevated co2 ameliorates o3-induced damage to leaf cells. the plants were exposed for 3 years at the aspen face exposure site in wisconsin (usa) prior to sampling for ultrastructural investigations on 19 june 1999. in the aspen clones, elevated co2 increased chloroplast cover index, leaf and spongy mesophyll layer thick ... | 2001 | 11789924 |
| effects of elevated co2 and o3 on aspen clones varying in o3 sensitivity: can co2 ameliorate the harmful effects of o3? | to determine whether elevated co2 reduces or exacerbates the detrimental effects of o3 on aspen (populus tremuloides michx.). aspen clones 216 and 271 (o3 tolerant), and 259 (o3 sensitive) were exposed to ambient levels of co2 and o3 or elevated levels of co2, o3, or co2 + o3 in the facts ii (aspen face) experiment, and physiological and molecular responses were measured and compared. clone 259. the most o3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as signifi ... | 2001 | 11789927 |
| ethyl m-digallate from red maple, acer rubrum l., as the major resistance factor to forest tent caterpillar, malacosoma disstria hbn. | an ethanolic extract of red maple (acer rubrum l.) leaves (rme) applied to trembling aspen (populus tremuloides michx.) leaves reduced feeding in choice test assays with forest tent caterpillar larvae (malacosoma disstria hbn.) (ftc), whereas a trembling aspen foliage extract, similarly applied, stimulated feeding. compounds isolated from the rme were gallic acid, methyl gallate, ethyl gallate, m-digallate, ethyl m-digallate, 1-o-galloyl-beta-d-glucose, 1-o-galloyl-alpha-l-rhamnose, kaempferol 3 ... | 2001 | 11789956 |
| simulation of 1-year-old populus tremuloides response to ozone stress at ithaca, usa, and suwon, republic of korea. | the growth of 1-year-old aspen was simulated using tregro, a computer simulation model of individual tree growth, to assess potential effects of ozone (o3). tregro was parameterized using information from a field experiment conducted at ithaca, ny, usa; the model was then applied using environmental information from suwon, korea, where o3 exposures of aspen had not been conducted. in the parameterization at ithaca, the simulated and measured total biomass differed by about 3% and the differences ... | 2001 | 11234543 |
| photosynthesis and carbon allocation of six boreal tree species grown in understory and open conditions. | one-year-old seedlings of abies balsamea (l.) mill, picea glauca (moench) voss, pinus contorta loudon, betula papyrifera marsh., populus tremuloides michx. and populus balsamifera l. were transplanted in the spring, in pots, to the understory of a mixed p. tremuloides-p. balsamifera stand or to an adjacent open site. growth and leaf characteristics were measured and photosynthetic light response curves determined in mid-august. overall, the coniferous seedlings showed less photosynthetic plastic ... | 2001 | 11276418 |
| differential substrate inhibition couples kinetically distinct 4-coumarate:coenzyme a ligases with spatially distinct metabolic roles in quaking aspen. | 4-coumarate:coenzyme a ligase (4cl) activates hydroxycinnamates for entry into phenylpropanoid branchways that support various metabolic activities, including lignification and flavonoid biosynthesis. however, it is not clear whether and how 4cl proteins with their broad substrate specificities fulfill the specific hydroxycinnamate requirements of the branchways they supply. two tissue-specific 4cls, pt4cl1 and pt4cl2, have previously been cloned from quaking aspen (populus tremuloides michx.), ... | 2002 | 11842147 |
| ethylene enhances water transport in hypoxic aspen. | water transport was examined in solution culture grown seedlings of aspen (populus tremuloides) after short-term exposures of roots to exogenous ethylene. ethylene significantly increased stomatal conductance, root hydraulic conductivity (l(p)), and root oxygen uptake in hypoxic seedlings. aerated roots that were exposed to ethylene also showed enhanced l(p). an ethylene action inhibitor, silver thiosulphate, significantly reversed the enhancement of l(p) by ethylene. a short-term exposure of ex ... | 2002 | 11891251 |
| photosynthetic acclimation of overstory populus tremuloides and understory acer saccharum to elevated atmospheric co2 concentration: interactions with shade and soil nitrogen. | we exposed populus tremuloides michx. and acer saccharum marsh. to a factorial combination of ambient and elevated atmospheric co2 concentrations ([co2]) and high-nitrogen (n) and low-n soil treatments in open-top chambers for 3 years. our objective was to compare photosynthetic acclimation to elevated [co2] between species of contrasting shade tolerance, and to determine if soil n or shading modify the acclimation response. sun and shade leaf responses to elevated [co2] and soil n were compared ... | 2002 | 11960756 |
| responses of deciduous broadleaf trees to defoliation in a co2 enriched atmosphere. | relatively little is known about the implications of atmospheric co2 enrichment for tree responses to biotic disturbances such as folivory. we examined the combined effects of elevated co2 concentration ([co2]) and defoliation on growth and physiology of sugar maple (acer saccharum marsh.) and trembling aspen (populus tremuloides michx.). seedlings were planted in the ground in eight open-top chambers. four chambers were ventilated with co2-enriched air (ambient + 283 micromol mol-1) and four ch ... | 2002 | 11986047 |
| coarse and fine root respiration in aspen (populus tremuloides). | coarse and fine root respiration rates of aspen (populus tremuloides michx.) were measured at 5, 15 and 25 degrees c. coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. to discriminate between maintenance and growth respiration, root respiration rates were measured during aboveground growing periods and dormant periods. an additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilizat ... | 2002 | 12091154 |
| independent activation of cold acclimation by low temperature and short photoperiod in hybrid aspen. | temperate zone woody plants cold acclimate in response to both short daylength (sd) and low temperature (lt). we were able to show that these two environmental cues induce cold acclimation independently by comparing the wild type (wt) and the transgenic hybrid aspen (populus tremula x populus tremuloides michx.) line 22 overexpressing the oat (avena sativa) phytochrome a gene. line 22 was not able to detect the sd and, consequently, did not stop growing in sd conditions. this resulted in an impa ... | 2002 | 12177476 |
| effects of soil temperature on parameters of a coupled photosynthesis-stomatal conductance model. | to examine the effects of soil temperature on a coupled photosynthesis-stomatal conductance model, seedlings of trembling aspen (populus tremuloides michx.), jack pine (pinus banksiana lamb.), black spruce (picea mariana (mill.) b.s.p.) and white spruce (picea glauca (moench) voss) were exposed to soil temperatures ranging from 5 to 35 degrees c for 4 months. light and co(2) response curves of foliar gas exchange were measured for model parameterization. the effects of soil temperature on four k ... | 2002 | 12184971 |
| environmental and auxin regulation of wood formation involves members of the aux/iaa gene family in hybrid aspen. | indole acetic acid (iaa/auxin) profoundly affects wood formation but the molecular mechanism of auxin action in this process remains poorly understood. we have cloned cdnas for eight members of the aux/iaa gene family from hybrid aspen (populus tremula l. x populus tremuloides michx.) that encode potential mediators of the auxin signal transduction pathway. these genes designated as pttiaa1-pttiaa8 are auxin inducible but differ in their requirement of de novo protein synthesis for auxin inducti ... | 2002 | 12220260 |
| leaf area dynamics of a boreal black spruce fire chronosequence. | specific leaf area (sla) and leaf area index (lai) were estimated using site-specific allometric equations for a boreal black spruce (picea mariana (mill.) bsp) fire chronosequence in northern manitoba, canada. stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. the goals of the study were to: (i) measure sla for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical condi ... | 2002 | 12359526 |
| differential expression of two distinct phenylalanine ammonia-lyase genes in condensed tannin-accumulating and lignifying cells of quaking aspen. | lignins, along with condensed tannins (cts) and salicylate-derived phenolic glycosides, constitute potentially large phenylpropanoid carbon sinks in tissues of quaking aspen (populus tremuloides michx.). metabolic commitment to each of these sinks varies during development and adaptation, and depends on l-phenylalanine ammonia-lyase (pal), an enzyme catalyzing the deamination of l-phenylalanine to initiate phenylpropanoid metabolism. in populus spp., pal is encoded by multiple genes whose expres ... | 2002 | 12376645 |