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At least 271 records · Page 15Linked to original sources
PubMed2006

Regeneration of the secondary vascular system in poplar as a novel system to investigate gene expression by a proteomic approach.

Wood formation is a complex process composing many biological events. To access its key developmental stages, we have established a regeneration system that can mimic the initiation and differentiation of cambium cells for Chinese white poplar. Anatomical studies showed that new cambium and xylem re-appeared in sequence within a few weeks after being debarked. This provides the opportunity to follow key stages of wood formation by sampling clonal trees at different regeneration times. We used this system in combination with a proteomic approach to analyze proteins expressed in different regeneration stages. PMFs for 244 proteins differentially displayed were obtained and queried against public databases. Putative functions of 199 of these proteins were assigned and classified. Regulatory genes for cell cycle progression, differentiation and cell fate were expressed in the formation of cambial tissue, while 27 genes involved in secondary wall formation were predominantly found in the xylem developing stage. This indicates that the change of gene expression pattern is corresponding to the progression of second vascular system regeneration when and where the key events of wood development occur. Further exploration of these interesting genes may provide insight into the molecular mechanisms of wood formation.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2002

A poplar plastocyanin mutant suitable for adsorption onto gold surface via disulfide bridge.

Aiming to achieve stable immobilization for a redox-active cupredoxin protein onto a gold substrate and its consequent molecular level monitoring by Scanning Tunnelling Microscopy (STM), we introduced a disulphide bridge within poplar plastocyanin, while avoiding the perturbation of its active site. We selected and modified residues Ile-21 to Cys and Glu-25 to Cys by structurally conservative mutagenesis. Optical absorption spectroscopy (UV-Vis), electron paramagnetic resonance (EPR), and resonance raman scattering (RRS) results indicate that the active site of the Ile21Cys, Glu25Cys plastocyanin (PCSS) to a large extent retains the spectroscopic properties of the wild-type protein. Furthermore, the redox midpoint potential of the couple CuII/CuI in PCSS, determined by cyclic voltammetry was found to be +348 mV close to the wild-type value. The STM images display self-assembled PCSS molecules immobilised onto gold substrate. Moreover, the full potentiostatic control of the electron transfer reaction during STM imaging, suggests that the adsorbed molecule maintains essentially its native redox properties.

Adsorption↗
PubMed1995

Tissue- and cell-specific expression of a cinnamyl alcohol dehydrogenase promoter in transgenic poplar plants.

Cinnamyl alcohol dehydrogenase (CAD) which catalyses the synthesis of the cinnamyl alcohols, the immediate precursors of lignins, from the corresponding cinnamaldehydes is considered to be a highly specific marker for lignification. We have isolated and characterized a CAD genomic clone from eucalyptus, a woody species of economic importance. The full-length promoter (EuCAD, 2.5 kb) and a series of 5' deletions were fused to the beta-glucuronidase (GUS) reporter gene. These constructs were tested in a homologous transient expression system of eucalyptus protoplasts which enabled the identification of several regions involved in transcriptional control. In order to study the spatial and developmental regulation of the CAD gene, the chimeric gene fusion (EuCAD-GUS) was then transferred via Agrobacterium tumefaciens-mediated transformation into poplar, an easily transformable woody angiosperm. Quantitative fluorometric assays conducted on eight independent in vitro transformants showed that GUS activity was highest in roots followed thereafter by stems and leaves. Histochemical staining for GUS activity on both in vitro primary transformants and more mature greenhouse-grown plants indicated a specific expression in the vascular tissues of stems, roots, petioles and leaves. At the onset of xylem differentiation, GUS activity was detected in parenchyma cells differentiating between the xylem-conducting elements. After secondary growth has occurred, GUS activity was localized in xylem ray cells and parenchyma cells surrounding the lignified phloem and sclerenchyma fibers. This first characterization of a woody angiosperm CAD promoter provides functional evidence for the role of CAD in lignification and suggests that parenchyma cells expressing CAD may provide lignin precursors to the adjacent lignified elements (vessels and fibres).

Alcohol Oxidoreductases↗
PubMed2005

Heavy metal concentrations in northern water snakes (Nerodia sipedon) from East Fork Poplar Creek and the Little River, East Tennessee, USA.

We compared the levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in the blood, kidney, liver, muscle, and skin of northern water snakes (Nerodia sipedon) collected from the upper reach of East Fork Poplar Creek (EFPC) within the United States Department of Energy's (USDOE's) Y-12 National Security Complex with concentrations in tissues of northern water snakes from a reference reach of the Little River downstream from the Great Smoky Mountains National Park in East Tennessee. Our objectives were to determine whether concentrations of these metals were higher in tissues of water snakes collected from EFPC compared with the reference site and if northern water snakes were suitable bioindicators of metal contamination. Except for chromium, metal levels were significantly higher in tissues (kidney, liver, muscle, and skin) of EFPC northern water snakes compared with those in tissues of snakes from the reference site. Although female northern water snakes were significantly larger than male snakes, their tissues did not contain significantly higher metal concentrations compared with those from male snakes, possibly because of maternal transfer of metals to eggs. This study was the first to examine the accumulation of contaminants resulting from the operations of the USDOE's Oak Ridge Reservation in snakes.

Animals↗
PubMed2003

Nutrient translocation in the xylem of poplar--diurnal variations and spatial distribution along the shoot axis.

This investigation shows diurnal variations in the xylem sap composition of poplar (Populus tremula x P. alba). All major macronutrients reached a maximum concentration in the first half of the light period and decreased to the middle of the night. The relative abundance of the nutrients did not change during the day. The sap flow, which responded very fast to the environmental changes (2.2-fold increase within 10-20 min of illumination), reached a maximum value in the second half of the light period. Transpiration (and photosynthesis) was constant throughout the light phase. The calculated translocation rates displayed a maximum in the first half of the light period and therefore did not fit the time course of sap flow. During the night, translocation rates were 63-69% lower than the maximum. The regulation of nutrient translocation is discussed taking the active xylem loading into account. The axial distribution located the nitrate assimilation in younger leaves and storage of nitrate (and other macronutrients) in older leaves. Nitrate and potassium concentrations in the xylem sap did not change along the plant axis. However, the sap flow was greater in younger shoot sections than in older sections. We assume that the greater demand for nitrate in the younger shoot section was satisfied via an increased volume flow rather an increased nitrate concentration.

Biological Transport↗
PubMed1998

Immunolocalization of cinnamyl alcohol dehydrogenase 2 (CAD 2) indicates a good correlation with cell-specific activity of CAD 2 promoter in transgenic poplar shoots.

Cinnamyl alcohol dehydrogenase 2 (CAD 2) localization and the cell-specific activity of the eucalyptus CAD 2 promoter were investigated by CAD 2 immunogold localization and promoter beta-glucuronidase (GUS) histochemistry in apical and mature parts of stable transformed poplar (Populus tremula x P. alba) stems. Both CAD 2 protein and GUS activity were found to be confined in the same types of cells in the shoot apices, particularly in the determined meristematic cells in leaf axils and shell zones, procambium and developing tracheids. Within mature stems, CAD 2 and GUS were also identified in cambium and in fully or partially lignified cells derived from it (young xylem, developing phloem fibres, chambered parenchyma cells around phloem). Additionally, GUS activity was found in the scale leaves of apical shoot buds and in the roots (namely in the procambium, cambium, phellogen, young xylem, pericycle) of transformed plants. By employing immunogold cytochemistry, CAD 2 was shown to be localized in the cytoplasm within cambial, ray and young xylem cells in stems, the gold particles being randomly attached to endoplasmic reticulum and Golgi-derived vesicles. These results support a crucial role for CAD 2 in lignification and indicate a new role for this enzyme in branching events within the shoot apex and during lateral root formation.

Alcohol Oxidoreductases↗
PubMed2001

First isolation of an isoprene synthase gene from poplar and successful expression of the gene in Escherichia coli.

For the first time, the complete functional gene for isoprene synthase has been isolated from poplar (Populus alba x Populus tremula). The gene was quite similar to known limonene and other monoterpene synthases, but was found to specifically catalyze the formation of isoprene from the precursor dimethylallyl diphosphate with only a marginal activity for the formation of the monoterpene limonene from geranyl diphosphate as compared with limonene synthases. Omitting the part of the gene that putatively encoded the signal peptide necessary for transport into the chloroplast led to an enhanced rate of isoprene formation by the recombinant protein.

Alkyl and Aryl Transferases↗
PubMed2005

Stomatal conductance and not stomatal density determines the long-term reduction in leaf transpiration of poplar in elevated CO2.

Using a free-air CO2 enrichment (FACE) experiment, poplar trees (Populus x euramericana clone I214) were exposed to either ambient or elevated [CO2] from planting, for a 5-year period during canopy development, closure, coppice and re-growth. In each year, measurements were taken of stomatal density (SD, number mm(-2)) and stomatal index (SI, the proportion of epidermal cells forming stomata). In year 5, measurements were also taken of leaf stomatal conductance (gs, micromol m(-2) s(-1)), photosynthetic CO2 fixation (A, mmol m(-2) s(-1)), instantaneous water-use efficiency (A/E) and the ratio of intercellular to atmospheric CO2 (Ci:Ca). Elevated [CO2] caused reductions in SI in the first year, and in SD in the first 2 years, when the canopy was largely open. In following years, when the canopy had closed, elevated [CO2] had no detectable effects on stomatal numbers or index. In contrast, even after 5 years of exposure to elevated [CO2], gs was reduced, A/E was stimulated, and Ci:Ca was reduced relative to ambient [CO2]. These outcomes from the long-term realistic field conditions of this forest FACE experiment suggest that stomatal numbers (SD and SI) had no role in determining the improved instantaneous leaf-level efficiency of water use under elevated [CO2]. We propose that altered cuticular development during canopy closure may partially explain the changing response of stomata to elevated [CO2], although the mechanism for this remains obscure.

Analysis of Variance↗
PubMed2004

Complete nucleotide sequence of the genomic RNA of poplar mosaic virus (Genus Carlavirus).

The complete nucleotide sequence of the Poplar mosaic virus (PopMV) genome was determined. The genomic RNA of PopMV is 8,742 nucleotides in length. Comparative sequence analysis supports earlier research suggesting that this virus is a member of the genus Carlavirus. For example, as is the case for all carlaviruses, there are 6 predicted ORFs in the PopMV genome. The first ORF, ORF1, encodes a predicted helicase/replicase, which corresponds to ORF1 from other carlaviruses, while ORF2, ORF3, ORF4, ORF5 and ORF6 encode the three triple block proteins, the coat protein, and a putative nucleic acid-binding protein respectively.

3' Untranslated Regions↗
PubMed2006

Genome histories clarify evolution of the expansin superfamily: new insights from the poplar genome and pine ESTs.

Expansins comprise a superfamily of plant cell wall-loosening proteins that has been divided into four distinct families, EXPA, EXPB, EXLA and EXLB. In a recent analysis of Arabidopsis thaliana and Oryza sativa expansins, we proposed a further subdivision of the families into 17 clades, representing independent lineages in the last common ancestor of monocots and eudicots. This division was based on both traditional sequence-based phylogenetic trees and on position-based trees, in which genomic locations and dated segmental duplications were used to reconstruct gene phylogeny. In this article we review recent work concerning the patterns of expansin evolution in angiosperms and include additional insights gained from the genome of a second eudicot species, Populus trichocarpa, which includes at least 36 expansin genes. All of the previously proposed monocot-eudicot orthologous groups, but no additional ones, are represented in this species. The results also confirm that all of these clades are truly independent lineages. Furthermore, we have used position-based phylogeny to clarify the history of clades EXPA-II and EXPA-IV. Most of the growth of the expansin superfamily in the poplar lineage is likely due to a recent polyploidy event. Finally, some monocot-eudicot clades are shown to have diverged before the separation of the angiosperm and gymnosperm lineages.

Arabidopsis↗
PubMed2006

Expression of poplar chitinase in tomato leads to inhibition of development in colorado potato beetle.

The previously described poplar chitinase, WIN6, is induced during infestation by gypsy moth (Lymantria dispar L.) larvae, thus suggesting a role in defense against insect pests. To test this hypothesis, we produced tomato seedlings infected with a recombinant potato virus X (PVX), which produces WIN6, and tested its insecticidal properties on Colorado potato beetle [CPB; Leptinotarsa decemlineata (Say)], which is a serious pest of tomatoes and other crops. The advantage of PVX is that plant material is ready for insect bioassay within 3-4 weeks of constructing the recombinant virus. Considering that production of transgenic tomato seedlings using Agrobacterium takes at least 6 months, this hastens the rate at which genes can be examined. Upon insect bioassay, only 47% CPB neonates feeding on leaves containing >0.3% w/w WIN6 developed to 2nd instar while 93% of controls reached 2nd instar. To our knowledge this is the first plant chitinase that retards development of an insect pest.

Animals↗
PubMed2005

How many samples are required? Evaluating a model for verification of carbon sequestration in a hybrid poplar buffer strip.

A model is developed to predict annual and total above-ground carbon storage within a hybrid poplar stream buffer. The regression model predicts tree wet weight based upon circumference at breast-height (137 cm) with an r-square value of 0.9922. Carbon storage in above-ground biomass is estimated to be 3.57 to 3.71 metric tons per hectare, with a measured annual increment of 0.92 to 1.37 metric ton per hectare per year. The variability of carbon storage within this biological system, including soil organic matter, is explored, and the number of samples required to achieve a desired level of statistical certainty are predicted. As has been investigated previously for other biological systems (Garten and Wullschleger, 1999), the study shows that a prohibitively large number of samples must be taken in order to achieve high degrees of certainty about mean carbon storage values. The study also shows, however, that mean values with somewhat greater uncertainties can easily be achieved with much smaller sample sizes. Thus carbon sequestration verification might be accomplished cost-effectively if the degree of certainty required is not unrealistically high for highly variable natural systems.

Carbon↗
PubMed2005

Effects of drought stress and nutrient availability on dry matter allocation, phenolic glycosides, and rapid induced resistance of poplar to two lymantriid defoliators.

The growth-differentiation balance hypothesis (GDBH) postulates that variation in resource availability can increase or decrease allocation to secondary metabolism, depending on how growth is affected relative to carbon assimilation. Growth and leaf area of black poplar (Populus nigra) increased substantially in response to increased nutrient availability, while net assimilation rate and photosynthesis were less strongly affected. In response, total phenolic glycoside concentrations declined, which is consistent with GDBH. Drought stress decreased net assimilation rate and photosynthesis as well as growth, while increasing total phenolic glycoside concentrations. This pattern does not follow GDBH, which predicts lower secondary metabolism when resource limitation decreases both growth and carbon assimilation. However, there was a strong negative correlation between growth and total phenolic glycoside concentration consistent with a trade-off between primary and secondary metabolism, a key premise of GDBH. Drought decreased the growth of gypsy moth (Lymantria dispar) larvae but had no effect on whitemarked tussock moth (Orgyia leucostigma). Increased nutrient availability had a positive linear effect on growth of whitemarked tussock moth, but no effect on gypsy moth. Treatment effects on gypsy moth corresponded closely with effects on total phenolic glycosides, whereas effects on whitemarked tussock moth more closely tracked changes in nutritional quality. Localized gypsy moth herbivory elicited rapid induced resistance to gypsy moth, with the effect being independent of water and nutrient availability, but did not affect whitemarked tussock moth, indicating that the effects of biotic and abiotic stress on insect resistance of trees can be species-specific.

Animals↗
PubMed1986

Crystal structure analyses of reduced (CuI) poplar plastocyanin at six pH values.

The structure of poplar plastocyanin in the reduced (CuI) state has been determined and refined, using counter data recorded from crystals at pH 3.8, 4.4, 5.1, 5.9, 7.0 and 7.8 (resolution 1.9 A, 1.9 A, 2.05 A, 1.7 A, 1.8 A and 2.15 A; the final residual R value was 0.15, 0.15, 0.16, 0.17, 0.16 and 0.15, respectively). The molecular and crystal structure of the protein is substantially the same in the reduced state as in the oxidized state. The refinements of the structures of the six forms of the reduced protein could therefore be commenced with a model derived from the known structure of CuII-plastocyanin. The refinements were made by reciprocal space least-squares calculations interspersed with inspections of electron-density difference maps. Precautions were taken to minimize any bias of the results of the refinements in the direction of the starting model. The most significant differences among the structures of the reduced protein at the six pH values, or between them and the structure of the oxidized protein, are concentrated at the Cu site. In the reduced protein at high pH (pH 7.8), the CuI atom is co-ordinated by the N delta(imidazole) atoms of His37 and His87, the S gamma(thiolate) atom of Cys84, and the S delta(thioether) atom of Met92, just as in CuII-plastocyanin. The distorted tetrahedral geometry and the unusually long Cu-S(Met92) bond are retained. The only effects of the change in oxidation state are a lengthening of the two Cu-N(His) bonds by about 0.1 A, and small changes in two bond angles involving the Cu-S(Cys) bond. The high-pH form of reduced plastocyanin accordingly meets all the requirements for efficient electron transfer. As the pH is lowered, the Cu atom and the four Cu-binding protein side-chains appear to undergo small but concerted movements in relation to the rest of the molecule. At low pH (pH 3.8), the CuI atom is trigonally co-ordinated by N delta(His37), S gamma(Cys84) and S delta(Met92). The fourth Cu-ligand bond is broken, the Cu atom making only a van der Waals' contact with the imidazole ring of His87. The trigonal geometry of the Cu atom strongly favours CuI, so that this form of the protein should be redox-inactive. This is known to be the case.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗
PubMed1988

Growth and physiological responses of yellow-poplar seedlings exposed to ozone and simulated acidic rain.

Nine-week-old, yellow-poplar (Liriodendron tulipifera L.) seedlings were exposed to ozone (O(3)) 4 h day(-1), 5 days week(-1), in combination with simulated rain (pH 3.0, 4.3, or 5.6, 1 h day(-1), 2 days week(-1), at 0.75 cm h(-1)) for 6 weeks, under controlled laboratory conditions. There was no main treatment effect of O(3) (<0.02, 0.05, 0.10, or 0.15 microlitre(-1)) on height growth or total plant biomass. However, specific leaf area increased linearly (P=0.05) with exposure of plants to increasing O(3) concentrations. Exposure of seedlings to 0.10 microl litre(-1) O(3) reduced the leaf area ratio and the stomatal conductance (S(c)), but increased the mean unit leaf rate compared to control plants. This O(3) concentration also caused S(c) to decrease more rapidly, relative to non-fumigated plants, in response to increasing vapor pressure deficit. The only main treatment effect caused by simulated rain was a linear decrease in S(c) with increasing acidity. For combined pollutant effects, O(3) applied at 0.05 or 0.10 microl litre(-1) resulted in significant (P=0.05) linear decreases in dry weights and relative growth rates (RGR) of stems and leaves, and in cumulative leaf area (LAI), as the solution pH decreased. Root to shoot ratio (RSR) decreased linearly, whereas stem RGR and LAI increased linearly in response to decreasing pH for seedlings exposed to 0.15 microl litre(-1) O(3). Seedlings treated with a pH 5.6 solution exhibited a linear decrease (P=0.05) in leaf dry weight and RGR and a linear increase (P=0.05) in RSR as O(3) concentrations increased.

Journal Article↗
PubMed1989

Free proline content and susceptibility of poplar (Populus) cuttings to the action of SO2, NaCl and PEG at different temperatures.

A study has been made of the influence of separate and simultaneous action of SO(2), NaCl and polyethylene glycol 8000 (PEG) on leaf injuries and free proline content of two poplar cuttings, Populus 'Robusta' and P. 'Hybrida 275', at an optimum (+15 degrees C), a lowered (+3 degrees C) and an increased (+35 degrees C) temperature. Proline accumulation was greatest in the most damaged cuttings of both cultivars for all three treatments. Simultaneous action of SO(2) and NaCl, as well as of SO(2) and PEG, caused significantly greater accumulation of this imino acid compared with the action of each factor separately, and the influence was more than additive. An increase in free proline content under the influence of the treatment combinations investigated here was proportional to the temperature during exposure. Greatest accumulation of proline under the experimental conditions was obtained by the simultaneous action of SO(2) and NaCl, as well as of SO(2) and PEG, at the temperature of 35 degrees C.

Journal Article↗
PubMed1993

Whole-plant growth and leaf formation in ozonated hybrid poplar (Populus x euramericana).

Seasonal growth was studied in potted cuttings of hybrid poplar (one clone of Populus x euramericana) either exposed to ozone in filtered air (0 = control, 0.05, 0.10 microl litre(-1)) or in ambient air (mean = 0.03 microl litre(-1)). Only at 0.10 microl litre(-1) was biomass production reduced and related to leaf loss rather than leaf formation, since the latter was similar in all treatments. Stem length at 0.10 microl litre(-1) approached that of the control, whereas starch concentration in the green stem bark tended to be reduced, as were the ratios of stem weight/length and root/shoot biomass. The changes in carbon allocation and biomass production gradually became established during the second half of the growing season. At the altered carbon allocation at 0.10 microl litre(-1), the ratio of whole-plant production/attached foliage area resembled that of the other O(3) regimes. However, the latter ratio was strongly reduced at 0.10 microl litre(-1) when calculated on the basis of the potential foliage area, as compensated for the O(3)-induced leaf loss. Thus the carbon return/cost balance of the totally formed foliage was low, although the relative-growth rate of ozonated plants temporarily reached that of the control. The relation between leaf differentiation under ozonation (lowered stomatal density) and whole-plant production remains uncertain. The plant behavior found is discussed in terms of passive response or acclimatization to O(3) stress.

Journal Article↗
PubMed2004

Experimental and numerical study of the poplar plastocyanin isoforms using Tyr as a probe for electrostatic similarity and dissimilarity.

A detailed study of the tyrosine spectral characteristics was carried out in a broad range of pHs for both isoforms of plastocyanin from poplar. It was found that Tyr 80 is always protonated while Tyr 83 can form a tirosinate at high pHs. The pK(a) of Tyr 83 is practically identical in plastocyanin a and b, but the quenching of its spectrum is different in the isoforms. This provides insights that the acidic patches surrounding Tyr 83 have different electrostatic properties in plastocyanin a and b. The protonation states and the electrostatic interactions were numerically modeled on the existing plastocyanin a structure and on a homology model of plastocyanin b. The results of numerical calculations agree with the experimental findings and identify several differences in the titration behavior of the acidic patches. The difference of the tyrosine quenching pH profiles of the isoforms is rationalized by the differences in the calculated pK(a)'s of amino acids in the neighboring acidic clusters.

Acrylamide↗