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PubMed2025

Factors underlying a latitudinal gradient in the S/G lignin monomer ratio in natural poplar variants.

The chemical composition of wood plays a pivotal role in the adaptability and structural integrity of trees. However, few studies have investigated the environmental factors that determine lignin composition and its biological significance in plants. Here, we examined the lignin syringyl-to-guaiacyl (S/G) ratio in members of a Populus trichocarpa population sourced from their native habitat and conducted a genome wide association study to identify genes linked to lignin formation. Our results revealed many significant associations, suggesting that lignin biosynthesis is a complex polygenic trait. Additionally, we found an increase in the S/G ratio from northern to southern geographic origin of the trees sampled, along with a corresponding metabolic and transcriptional reprogramming of xylem cell wall biosynthesis. Further molecular analysis identified a mutation in a cell wall laccase genetically associated with higher S/G ratios that predominate in trees from warmer lower latitudes. Collectively, our findings suggest that lignin heterogeneity arises from an evolutionary process enabling poplar adaptation to different climatic challenges.

Populus↗

PubMed2006

Functional and structural aspects of poplar cytosolic and plastidial type a methionine sulfoxide reductases.

The genome of Populus trichocarpa contains five methionine sulfoxide reductase A genes. Here, both cytosolic (cMsrA) and plastidial (pMsrA) poplar MsrAs were analyzed. The two recombinant enzymes are active in the reduction of methionine sulfoxide with either dithiothreitol or poplar thioredoxin as a reductant. In both enzymes, five cysteines, at positions 46, 81, 100, 196, and 202, are conserved. Biochemical and enzymatic analyses of the cysteine-mutated MsrAs support a catalytic mechanism involving three cysteines at positions 46, 196, and 202. Cys(46) is the catalytic cysteine, and the two C-terminal cysteines, Cys(196) and Cys(202), are implicated in the thioredoxin-dependent recycling mechanism. Inspection of the pMsrA x-ray three-dimensional structure, which has been determined in this study, strongly suggests that contrary to bacterial and Bos taurus MsrAs, which also contain three essential Cys, the last C-terminal Cys(202), but not Cys(196), is the first recycling cysteine that forms a disulfide bond with the catalytic Cys(46). Then Cys(202) forms a disulfide bond with the second recycling cysteine Cys(196) that is preferentially reduced by thioredoxin. In agreement with this assumption, Cys(202) is located closer to Cys(46) compared with Cys(196) and is included in a (202)CYG(204) signature specific for most plant MsrAs. The tyrosine residue corresponds to the one described to be involved in substrate binding in bacterial and B. taurus MsrAs. In these MsrAs, the tyrosine residue belongs to a similar signature as found in plant MsrAs but with the first C-terminal cysteine instead of the last C-terminal cysteine.

Cloning, Molecular↗

PubMed2003

Physiological condition and water source use of Sonoran Desert riparian trees at the Bill Williams River, Arizona, USA.

We investigated the environmental water sources used in mid-summer by three Sonoran Desert phreatophytic riparian tree species, Salix gooddingii, Populus fremontii, and the exotic Tamarix spp., at sites that differed in water table depth. Salix gooddingii was most sensitive to water table decline, as evidenced by lower predawn water potentials. Although P. fremontii was less sensitive to water table decline than S. gooddingii, its leaf gas exchange was the most responsive to atmospheric water stress imposed by high leaf-to-air vapor pressure deficit. Tamarix spp. was least sensitive to water table decline and showed no reduction of predawn water potential over the measured range of depth to groundwater. Comparison between D/H of xylem and sampled environmental water sources suggest that S. gooddingii and P. fremontii used groundwater at most sites with no change in water source as depth to groundwater varied. In contrast, xylem D/H of Tamarix spp. was depleted in deuterium compared to groundwater at most sites, suggesting use of water from an unsampled source, or discrimination against deuterium during water uptake. This study highlights the difficulty in sampling all water sources in large-scale studies of riparian ecosystems with complex subsurface hydrogeology.

Adaptation, Physiological↗

PubMed2003

Stimulation of hybrid poplar growth in petroleum-contaminated soils through oxygen addition and soil nutrient amendments.

Hybrid poplar trees (Populus deltoides x nigra DN34) were grown in a green-house using hydrocarbon-contaminated soil from a phytoremediation demonstration site in Health, Ohio. Two independent experiments investigated the effect of nutrient addition on poplar growth and the importance of oxygen addition to root development and plant growth. Biomass measurements, poplar height, and leaf color were used as indicators of plant health in the selection of a 10/5/5 NPK fertilizer applied at 1121 kg/ha (112 kg-N, 24.4 kg-P, 46.5 kg-K per ha) to enhance hybrid poplar growth at the Health site. Five passive methods of oxygen delivery were examined, including aeration tubes, gravel addition, and an Oxygen Release Compound (ORC). When ORC was placed in coffee filters above hydrocarbon-contaminated soil, a statistically significant increase of 145% was observed in poplar biomass growth, relative to unamended controls. The ORC in filters also stimulated significant increases in root density. A 15.2-cm interval of soil directly below ORC addition exhibited an increase from 2.6 +/- 1.0 mg/cm3 to 4.8 +/- 1.0 mg/cm3, showing stimulation of root growth in hydrocarbon-stained soil. The positive response of hybrid poplars to oxygen amendments suggests that overcoming oxygen limitation to plants should be considered in phytoremediation projects when soil contamination exerts a high biochemical oxygen demand, such as in former refinery sites.

Biodegradation, Environmental↗

PubMed2005

Clonal variation in survival and growth of hybrid poplar and willow in an in situ trial on soils heavily contaminated with petroleum hydrocarbons.

Species and hybrids between species belonging to the genera Populus (poplar) and Salix (willow) have been used successfully for phytoremediation of contaminated soils. Our objectives were to: 1) evaluate the potential for establishing genotypes of poplar and willow on soils heavily contaminated with petroleum hydrocarbons and 2) identify promising genotypes for potential use in future systems. We evaluated height, diameter, and volume after first year budset by testing 20 poplar clones and two willow clones. Unrooted cuttings, 20 cm long, were planted in randomized complete blocks at 0.91- x 0.91-m spacing at Gary, IN, USA (41.5 degrees N, 87.3 degrees W). Four commercial poplar clones (NM6, DN5, DN34, and DN182) were planted as 20- and 60-cm cuttings. Sixty-cm cuttings exhibited greater height and diameter than 20-cm cuttings; however, we recommend continued use and testing of different combinations of genotype and cutting length. We identified promising genotypes for potential use in future systems and we recommend allocating the majority of resources into commercial poplar clones, given their generalist growth performance. However, further utilization and selection of experimental clones is needed. Specific clones rather than genomic groups should be selected based on the geographic location and soil conditions of the site.

Biodegradation, Environmental↗

PubMed2005

Assessing the potential of short rotation coppice (SRC) for cleanup of radionuclide-contaminated sites.

A small-scale greenhouse investigation was undertaken using Goat willow (Salix caprea) and aspen (Populus tremula) to evaluate the potential of short rotation coppice for remediation of 137Cs- and 90Sr-contaminated sites. Results showed that both species were able to accumulate these radionuclides from a representative disposal soil (aged) and a spiked soil S. caprea accumulating greater levels of 137Cs than P. tremula, with no difference between species for 90Sr accumulation. For each radionuclide, the distribution in both species was similar, with 137Cs accumulation greatest in the roots, whereas 90Sr accumulation was greatest in the leaves. It was also evident that the soil-to-plant transfer factor (Tf) values for 90Sr were greater than for 137Cs, agreeing with differences in the reported bioavailailablity of these radionuclides in soil Based on the Tf values for S. caprea (conservative), estimated remediation times were 92 and 56 yr, for 137Cs and 90Sr, respectively. It is suggested that the selection of Salix species grown in a system of SRC provides a significant opportunity for removal of both 137Cs and 90Sr, primarily due to its higher biomass production. However, for 137Cs phytoremediation investigations into the appropriate use of soil amendments for increasing bioavailability are required.

Populus↗

PubMed2002

A preliminary investigation of the role of auxin and cytokinin in sylleptic branching of three hybrid poplar clones exhibiting contrasting degrees of sylleptic branching.

Sylleptic branches grow out from lateral buds during the same growing season in which the buds are formed. This type of branching is present in poplar and in many tropical species. It results in the production of more branches, more leaves and expanded photosynthetic capacity and is thought to assist in increasing the overall growth and biomass of the tree at a young age. However, very little is known about the physiology of sylleptic branching in poplar, which is an extremely important source of fibre and fuel. In the present study of three hybrid poplar clones (11-11, 47-174 and 49-177) of Populus trichocarpa x P. deltoides exhibiting contrasting degrees of sylleptic branching, an analysis was carried out on parent shoot elongation and sylleptic branching, together with a preliminary comparison of the parent shoots' sensitivity to auxin (naphthaleneacetic acid) as a repressor of lateral bud outgrowth, and cytokinin (benzyladenine) as a promoter. Suggestive evidence was found for an inverse correlation between parent shoot sensitivity to auxin and the degree of sylleptic branching, as well as a partially positive correlation with respect to sensitivity to cytokinin. The present data are consistent with the hypothesis that auxin and cytokinin may play repressive and promotive roles, respectively, in the sylleptic branching of hybrid poplar.

Adenine↗

PubMed2003

Isolation and characterization of a new, full-length cellulose synthase cDNA, PtrCesA5 from developing xylem of aspen trees.

Cellulose synthases (CesA) represent a group of beta-1,4 glycosyltransferases involved in cellulose biosynthesis. Recent molecular studies confirmed that a large CesA gene family encoding various CesA isoforms exists in plants. The isolation and characterization of a new, full-length CesA cDNA, PtrCesA5 from an economically important tree, quaking aspen (Populus tremuloides) is reported here. The predicted PtrCesA5 protein is highly similar to Arabidopsis AtCesA3 (88%) involved in primary cell wall synthesis. However, gene expression studies here suggest that PtrCesA5 transcripts are greatly enhanced in developing xylem tissues enriched in secondary cell wall synthesis as compared with leaf tissues actively undergoing primary cell wall synthesis. Availability of this new, dual-function CesA from a woody species will assist in a better understanding of the mechanism of cellulose biosynthesis during wood development.

DNA, Complementary↗

PubMed2006

Genome-wide analysis of plant glutaredoxin systems.

The recent release of the first tree genome (Populus trichocarpa) has allowed a comparison to be made of the multigenic glutaredoxin (Grx) and glutathione reductase (GR) families of this tree with those of other sequenced organisms and especially of the two other fully sequenced plant species, Arabidopsis thaliana and Oryza sativa. Grxs are small proteins involved in disulphide bridge or protein-glutathione adduct reduction, and they are maintained in a reduced form using glutathione and an NADPH-dependent GR. While the P. trichocarpa and O. sativa genomes are nearly five times larger than that of A. thaliana, they contain approximately 45 000 and 37 500 genes compared with the 25 500 genes of A. thaliana. On the one hand, the GR gene composition varies little between species and the gene structures are relatively conserved. On the other hand, the Grx gene family can be divided into three subgroups and the gene content is larger in P. trichocarpa (36 genes) compared with A. thaliana and O. sativa (31 and 27 genes, respectively). This could be partly explained by the occurrence of more duplication events, and this is especially true for one of the three identified Grx subgroups (subgroup III). The expression of most of these genes was confirmed by analysing expressed sequence tags present in various databases. In addition, the expression of Grx of subgroups I and II was examined by RT-PCR in various poplar organs. A complete classification based essentially on gene structure and sequence identity is proposed.

Amino Acid Sequence↗

PubMed2025

Evolutionary Genomics Unravels the Responses and Adaptation to Climate Change in a Key Alpine Forest Tree Species.

Despite widespread biodiversity loss, our understanding of how species and populations will respond to accelerated climate change remains limited. In this study, we integrate population genomics, experimental evolution, and environmental modeling to elucidate the evolutionary responses to climate change in Populus lasiocarpa, a key alpine forest tree species primarily distributed in the mountainous regions of a global biodiversity hotspot. Over historical timescales, our findings demonstrate that demographic dynamics, divergent selection, and long-term balancing selection have shaped and maintained genetic variation within and between populations. In examining genomic signatures of contemporary climate adaptation, we found that haplotype blocks, potentially caused by inversion polymorphisms that suppress recombination, are linked to enriched combinations of locally adaptive environmental variations. We further assessed the relative contributions of environmentally induced plastic responses, constitutive expression divergence between genetic clusters, and their interactions in driving gene expression variation and divergence. Notably, we observed a strong correlation between sequence divergence and constitutive differential expression among genetic clusters. Finally, by incorporating genetic adaptation, migration, and genetic load into our predictions of population-level climate change risks, we identified western populations-primarily distributed in the Hengduan Mountains, a region known for its environmental heterogeneity and significant biodiversity-as the most vulnerable to climate change. These populations should be prioritized for conservation and management. Overall, our study advances the understanding of the relative roles of long-term natural selection, local environmental adaptation, and immediate plastic expression changes in shaping the responses of natural populations of keystone species to climate change.

Climate Change↗

PubMed2004

Characterization of full-length enriched expressed sequence tags of stress-treated poplar leaves.

Poplar, whose genome is the first to be sequenced among woody plants, is a favorable model for plant biologists to enable them to understand molecular processes of growth, development and responses to environmental stimuli in trees. The sequence will allow the development of a strategy for improving environmental stress tolerance in forest trees. In this study, we have generated a full-length enriched cDNA library from leaves of axenically grown poplar (Populus nigra var. italica) subjected to environmental stress treatments by dehydration, high salinity, chilling, heat, abscisic acid (ABA) and H2O2. We sequenced >30,000 expressed sequence tags (ESTs) from the cDNA library and consequently collected approximately 4,500 non-redundant clones. We further analyzed cDNAs encoding an ERF/AP2-domain transcription factor which is specific in plants and plays an important role under stress. Thirteen candidates containing the ERF/AP2 domain were found within our EST resource. Some of them showed stress-responsive gene expression. We report here the first collection of full-length enriched stress-related ESTs of poplar and discuss environmental stress responses of forest trees in the light of comparative genomics.

Abscisic Acid↗

PubMed2005

Clarification of cinnamoyl co-enzyme A reductase catalysis in monolignol biosynthesis of Aspen.

Cinnamoyl co-enzyme A reductase (CCR), one of the key enzymes involved in the biosynthesis of monolignols, has been thought to catalyze the conversion of several cinnamoyl-CoA esters to their respective cinnamaldehydes. However, it is unclear which cinnamoyl-CoA ester is metabolized for monolignol biosynthesis. A xylem-specific CCR cDNA was cloned from aspen (Populus tremuloides) developing xylem tissue. The recombinant CCR protein was produced through an Escherichia coli expression system and purified to electrophoretic homogeneity. The biochemical properties of CCR were characterized through direct structural corroboration and quantitative analysis of the reaction products using a liquid chromatography-mass spectrometry system. The enzyme kinetics demonstrated that CCR selectively catalyzed the reduction of feruloyl-CoA from a mixture of five cinnamoyl CoA esters. Furthermore, feruloyl-CoA showed a strong competitive inhibition of the CCR catalysis of other cinnamoyl CoA esters. Importantly, when CCR was coupled with caffeoyl-CoA O-methyltransferase (CCoAOMT) to catalyze the substrate caffeoyl-CoA ester, coniferaldehyde was formed, suggesting that CCoAOMT and CCR are neighboring enzymes. However, the in vitro results also revealed that the reactions mediated by these two neighboring enzymes require different pH environments, indicating that compartmentalization is probably needed for CCR and CCoAOMT to function properly in vivo. Eight CCR homologous genes were identified in the P. trichocarpa genome and their expression profiling suggests that they may function differentially.

Acyl Coenzyme A↗

PubMed2002

Partitioning of nitrate assimilation among leaves, stems and roots of poplar.

Plants differ in tissue localization of nitrate reduction and assimilation. Some species reduce nitrate primarily in the leaves, whereas other species localize nitrate reduction and assimilation in the roots. We determined how nitrate assimilation is partitioned among leaves, stems and roots of poplar (Populus tremula L. x P. alba L.) by comparing tissue differences in in vivo nitrate reductase activity (NRA), nitrate reductase abundance and tissue nitrate concentration. Compared with stems or roots, NRA was greater in leaves, and the highest leaf NRA was found in young leaves. Leaf and root NRA increased with increasing nitrate supply, whereas stem NRA remained constant. Leaf NRA was at least 10-fold greater than root NRA at all external nitrate concentrations. Nitrate reductase abundance increased in all tissues with increasing nitrate availability, and nitrate reductase abundance was at least 10-fold greater in leaves than in stems or roots at all nitrate availabilities. Tissue nitrate concentration increased with increasing nitrate supply and was greater in roots than in stems and leaves. Photoperiod influenced NRA, with leaf NRA declining in nitrate-fertilized plants with short daily photoperiods (8-h). We conclude that different tissues of poplar vary in nitrate assimilation with little nitrate assimilation occurring in roots and the most nitrate assimilation taking place in leaves.

Nitrate Reductase↗

PubMed2002

Carbohydrates in individual poplar fine roots: effects of root age and defoliation.

Late-summer starch accumulation in fine roots of poplars (Populus x canadensis Moench.) defoliated by gypsy moth (Lymantria dispar L.) lagged behind that in fine roots of undefoliated trees. If starch concentration declines with age, defoliation-induced changes in root system age structure could be partly responsible for this difference. To test this hypothesis, we measured fine-root starch and soluble sugar concentrations in roots of known age from trees in defoliated and undefoliated plots. There was a significant interaction between the effects of defoliation and root type (white, brown, or dead) on fine root soluble sugar concentration because of the high concentration of soluble sugars in white roots from trees in undefoliated plots. Both root starch and soluble sugar concentrations were variable among individuals of each age class. The population frequency distributions for starch and soluble sugar concentrations were both right-skewed, and fit by exponential functions. These data are most consistent with direct defoliation effects on a labile and dynamic pool of carbohydrates in poplar fine roots, rather than indirect defoliation effects on root system age structure.

Carbohydrates↗

PubMed2002

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 key model parameters, V(cmax) (maximum rate of carboxylation), J(max) (maximum rate of electron transport), alpha (energy conversion efficiency or quantum efficiency of electron transport) and R(d) (daytime dark respiration), were modeled using two third-order polynomial equations and a modified Arrhenius equation. In all species, V(cmax) and J(max) increased with soil temperature up to an optimum, and then decreased with further increases in soil temperature. In the conifers, alpha showed a similar response to soil temperature as V(cmax) and J(max), but soil temperature had no significant effect on alpha in aspen. Soil temperature had no significant effect on R(d) in any species. The three equations described the relationships between soil temperature and the model parameters reasonably well, but performed best for V(cmax) and worst for alpha. No significant relationships were identified between soil temperature and the parameters of the stomatal conductance model.

Carbon Dioxide↗

PubMed2002

Radial patterns of sap flow in woody stems of dominant and understory species: scaling errors associated with positioning of sensors.

We studied sap flow in dominant coniferous (Pinus sylvestris L.) and broadleaf (Populus canescens L.) species and in understory species (Prunus serotina Ehrh. and Rhododendron ponticum L.) by the heat field deformation (HFD) method. We attempted to identify possible errors arising during flow integration and scaling from single-point measurements to whole trees. Large systematic errors of -90 to 300% were found when it was assumed that sap flow was uniform over the sapwood depth. Therefore, we recommend that the radial sap flow pattern should be determined first using sensors with multiple measuring points along a stem radius followed by single-point measurements with sensors placed at a predetermined depth. Other significant errors occurred in the scaling procedure even when the sap flow radial pattern was known. These included errors associated with uncertainties in the positioning of sensors beneath the cambium (up to 15% per 1 mm error in estimated xylem depth), and differences in environmental conditions when the radial profile applied for integration was determined over the short term (up to 47% error). High temporal variation in the point-to-area correction factor along the xylem radius used for flow integration is also problematic. Compared with midday measurements, measurements of radial variation of sap flow in the morning and evening of sunny days minimized the influence of temporal variations on the point-to-area correction factor, which was especially pronounced in trees with a highly asymmetric sap flow radial pattern because of differences in functioning of the sapwood xylem layers. Positioning a single-point sensor at a depth with maximum sap flow is advantageous because of the high sensitivity of maximum sap flow to water stress conditions and changes in micro-climate, and because of the lower random errors associated with the positioning of a single-point sensor along the xylem radius.

Pinus↗

PubMed2002

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 conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest.

Ecosystem↗

PubMed2002

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 chambers were supplied with ambient air. After 6 weeks of growth, half of the leaf area was removed on a subset of seedlings of each species in each CO2 treatment. We monitored subsequent biomass gain and allocation, along with leaf gas exchange and chemistry. Defoliation did not significantly affect final seedling biomass in either species or CO2 treatment. Growth recovery following defoliation was associated with increased allocation to leaf mass in maple and a slight enhancement of mean photosynthesis in aspen. Elevated [CO2] did not significantly affect aspen growth, and the observed stimulation of maple growth was significant only in mid-season. Correspondingly, simulated responses of whole-tree photosynthesis to elevated [CO2] were constrained by a decrease in photosynthetic capacity in maple, and were partially offset by reductions in specific leaf area and biomass allocation to foliage in aspen. There was a significant interaction between [CO2] and defoliation on only a few of the measured traits. Thus, the data do not support the hypothesis that atmospheric CO2 enrichment will substantially alter tree responses to folivory. However, our findings do provide further indication that regeneration-stage growth rates of certain temperate tree species may respond only moderately to a near doubling of atmospheric [CO2].

Acer↗