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PubMed2001

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 thickness, intercellular air space volume in mesophyll, amount of starch in chloroplasts and cytoplasmic lipids but decreased the number of plastoglobuli in chloroplasts. In contrast, elevated O3 decreased chloroplast cover index, starch content, and the proportion of cytoplasm and intercellular space in mesophyll, and increased the proportion of vacuoles, the amount of condensed vacuolar tannins and the number of plastoglobuli. Ozone also caused structural thylakoid injuries (dilation, distortion) and stromal condensation in chloroplasts, which was ameliorated by elevated CO2 by 5-66% in aspen clones and by 2-10% in birch. Birch ultrastructure was less affected by elevated CO2 or O3 stress compared to aspen. In the most O3-sensitive aspen clone, thinner leaves and cell walls, lower proportion of cell wall volume, and higher volume for vacuoles was found compared to more-tolerant clones.

Air Pollutants↗

PubMed2002

[Populus nigra L. in the Garonne valley: legacy of the past and present constraints].

This study used documents from archives and historical maps to follow the simultaneous change of the riparian woodlands (where Populus nigra is dominant) and the poplar plantations. Results showed that the riparian woodland decreased by 81% over the two last centuries. Each period was characterised by the dominance of only a few number of clones. The risk of introgression due to the massive presence of such a restricted genetic material around P. nigra was discussed. The impact of river management on poplar regeneration was examined as well.

Climate↗

PubMed2000

Quantitative genetic variation of leaf size and shape in a mixed diploid and triploid population of Populus.

In the interspecific cross of Populus trichocarpa x P. deltoides, unexpected simultaneous occurrence of diploid hybrids and triploid hybrids (with two alleles from the female parent and one from the male parent at each locus) led us to examine the evolutionary genetic significance of this phenomenon. As expected, leaf size and shape of the triploid progeny are closer to the female P. trichocarpa than male P. deltoides parent. Although the pure triploid progeny population did not have higher genetic variance in leaf traits than the pure diploid population, the former appears to hide much non-additive genetic variance and display strong genetic control over the phenotypic plasticity of leaf traits. It is suggested that the cryptic non-additive variance, especially epistasis, can be released when a population is disturbed by changes in the environment. A mixed diploid and triploid progeny population combines phenotypic and genetic characteristics of both pure hybrids and is considered to be of adaptive significance for populars to survive and evolve in a fluctuating environment. The significant effect due to general and specific combining ability differences at the population level suggests that the population divergence of these two species is under additive and non-additive genetic control.

Diploidy↗

PubMedDate not supplied

Plant antiviral agents, VI. Isolation of antiviral phenolic glucosides from Populus cultivar Beaupre by droplet counter-current chromatography.

Bioassay-guided isolation of the 80% EtOH extract of the leaves of Populus cultivar Beaupré by means of dccc afforded four known phenolic glucosides. Salicin and salireposide were shown to be, at least partially, responsible for the antiviral activity of the extract against poliomyelitis and Semliki forest viruses.

Antiviral Agents↗

PubMed1997

Molecular cloning and biochemical characterization of carbonic anhydrase from Populus tremula x tremuloides.

A leaf cDNA library from hybrid aspen, Populus tremula x tremuloides, was constructed. From this two different cDNA clones, denoted CA1a and CA1b, encoding a chloroplastic carbonic anhydrase (CA) were isolated and DNA sequenced. Analysis of the deduced amino acid sequences showed that the isolated CAs belong to the beta-CA family, and have identities around 70% to other dicotyledonous plant CAs. The two hybrid aspen cDNA clones display a high nucleotide sequence identity, only 12 nucleotides differ. Since only one gene copy of this soluble chloroplastic CA is present in the nuclear genome, we postulate that the two isolated cDNA clones are alleles. Northern blot hybridization revealed a CA transcript of ca. 1300 bases, 140 bases shorter than in pea. Western and northern blot hybridizations on crude protein extracts and on total RNA, respectively, isolated from stem and leaves, showed that hybrid aspen CA is expressed specifically in the leaf under the growth conditions used. Based on the deduced amino acid sequence, the mature hybrid aspen CA enzyme subunit has a molecular mass of 24.8 kDa. The enzyme was over-expressed in Escherichia coli, and purified by affinity chromatography. Biochemical characterization showed that the protein structure and the CO2-hydration activity are similar to the pea enzyme. Molecular characterization of a CA from a perennial plant has not previously been performed, and it demonstrates that both the structure and activity of hybrid aspen CA resembles CAs from annual plants.

Amino Acid Sequence↗

PubMed2001

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 and its product shown to inhibit bovine trypsin in vitro. Both classes of PtTI genes are induced by wounding and herbivory, permitting rapid adaptive responses to herbivore pressure. The response appears to be mediated by an octadecanoid-based signaling pathway, as methyl jasmonate treatments induced the trypsin inhibitors. Wound-induced accumulation of trypsin inhibitor protein was also observed by western blot analysis. The pattern of expression, the apparent rapid evolution of TI genes, and the in vitro trypsin inhibitory activity are consistent with a role in herbivore defense. This work establishes the presence of a functional protein-based inducible defense system in trembling aspen.

Acetates↗

PubMed2001

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 treatment. Wound induction was systemic, and occurred in unwounded leaves on wounded plants. This pattern of expression is consistent with a role of this enzyme in insect defense. A search for potential PPO substrates in ethanolic aspen leaf extracts using electron spin resonance (ESR) found no pre-existing diphenolic compounds. However, following a brief delay and several additions of oxygen, an ESR signal specific for catechol was detected. The source of this catechol was most likely the aspen phenolic glycosides tremulacin or salicortin which decomposed during ESR experiments. This was subsequently confirmed in experiments using pure salicortin.

Journal Article↗

PubMed2003

Fluoride inhibits root water transport and affects leaf expansion and gas exchange in aspen (Populus tremuloides) seedlings.

The effects of sodium fluoride (0.3, 5 and 10 mM NaF) on root hydraulic conductivity, and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. A long-term exposure of roots to NaF significantly decreased root hydraulic conductivity (Lp) and stomatal conductance ( gs). Root absorbed NaF significantly affected electrolyte leakage in leaf tissues and substantially restricted leaf expansion. NaF did not significantly affect leaf chlorophyll contents but decreased net photosynthesis (Pn). A short-term exposure of excised roots to 5 mM NaF and KF significantly decreased root water flow (Qv) with a concomitant decline in root respiration and reduced gs when applied through intact roots or excised stems. The same molar concentration of NaCl also decreased Qv and gs in intact seedlings, but to a lesser extent than NaF or KF, and did not significantly affect root respiration. The results suggest that fluoride metabolically inhibited Qv or Lp, probably by affecting water channel activity. We suggest that the metabolic inhibition of Lp by root-absorbed fluoride affected gas exchange and leaf expansion in aspen seedlings.

Journal Article↗

PubMed2003

Stem respiration of Populus species in the third year of free-air CO2 enrichment.

Carbon cycling in ecosystems, and especially in forests, is intensively studied to predict the effects of global climate change, and the role which forests may play in 'changing climate change'. One of the questions is whether the carbon balance of forests will be affected by increasing atmospheric CO2 concentrations. Regarding this question, effects of elevated [CO2] on woody-tissue respiration have frequently been neglected. Stem respiration of three Populus species (P. alba L. (Clone 2AS-11), P. nigra L. (Clone Jean Pourtet), and P. x euramericana (Clone I-214)) was measured in a managed, high-density forest plantation exposed to free-air CO2 enrichment (POPFACE). During the period of measurements, in May of the third year, stem respiration rates were not affected by the FACE treatment. Moreover, FACE did not influence the relationships between respiration rate and both stem temperature and relative growth rate. The results were supported by the reported absence of a FACE-effect on growth and stem wood density.

Journal Article↗

PubMed1999

Genetic variation of the riparian pioneer tree species populus nigra. II. Variation In susceptibility to the foliar rust melampsora larici-populina

Partial resistance of Populus nigra L. to three races of the foliar rust Melampsora larici-populina Kleb. was studied in a field trial and in laboratory tests, using a collection of P. nigra originating from different places throughout France. No total resistance was found. The partial resistance was split into epidemiological components, which proved to be under genetic control. Various patterns of association of epidemiological components values were found. Principal components analysis revealed their relationships. Only 24% of the variance of the field susceptibility could be explained by the variation of the epidemiological components of susceptibility. This variable was significantly correlated with susceptibility to the most ancient and widespread race of the pathogen, and with the variables related to the size of the lesions of the different races. Analysis of variance showed significant differences in susceptibility between regions and between stands within one region. Up to 20% of variation was between regions, and up to 22% between stands, so that these genetic factors appeared to be more differentiated than the neutral diversity (up to 3.5% Legionnet & Lefevre, 1996). However, no clear pattern of geographical distribution of diversity was detected.

Journal Article↗

PubMed1998

Molecular characterisation of a novel plant homeobox gene expressed in the maturing xylem zone of Populus tremula x tremuloides.

In trees, wood is produced from the vascular cambium. However, little is known about how differentiation of the cambial derivatives is controlled at the molecular level. Hybrid aspen, Populus tremula x tremuloides, is a fast-growing, wood-forming plant from which an efficient transformation and regeneration protocol has been developed. We use this species as a model to study xylem cell differentiation. In a cross-section of the stem, cells in the cambial region at different stages of development can be seen in a radial distribution. We dissected out the cambial region and constructed a cDNA-library from this tissue. The library was screened with a degenerated primer mix complementary to the third helix region of the homeobox. A number of cDNAs hybridising to the probe were isolated, purified, cloned and sequenced. Characterisation of the expression pattern of two such homeobox cDNAs revealed that one of the cDNAs, denoted PttHB1, was specifically expressed in the xylem maturation zone, indicating a role in the regulation of secondary wall formation, while the other, denoted PttHB2 was expressed in differentiating xylem and phloem cells. Structurally, the two hybrid aspen homeobox genes are homologous to each other, but no close relationship could be identified between these genes and any other homeobox sequence described thus far, in plants or other eukaryotes. We therefore conclude that the PttHB1 and PttHB2 genes belong to a novel hitherto undescribed sequence class of homeobox genes. We designate this as PALE.

Amino Acid Sequence↗

PubMed2000

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 transcripts in various aspen tissues, and PtCesA gene promoter-beta-glucuronidase (GUS) fusion analysis in transgenic tobacco, demonstrated conclusively that PtCesA expression is confined to developing xylem cells during normal plant growth. During mechanical stress induced by stem bending, GUS expression remained in xylem and was induced in developing phloem fibers undergoing tension stress, but was turned off in tissues undergoing compression on the opposite side of the bend. Our results suggest a unique role for PtCesA in cellulose biosynthesis in both tension-stressed and normal tissues in aspen, and that the on/off control of PtCesA expression may be a part of a signaling mechanism triggering a stress-related compensatory deposition of cellulose and lignin that is crucial to growth and development in trees.

Arabidopsis Proteins↗

PubMed2003

Expression of Vitreoscilla haemoglobin in hybrid aspen (Populus tremula x tremuloides).

We describe the first ever expression of Vitreoscilla haemoglobin (VHb) in an economically important boreal woody plant hybrid aspen (Populus tremula x tremuloides). VHb has mainly been expressed in biotechnologically important unicellular organisms of both prokaryotic and eukaryotic origin. VHb expression, in this study, was analysed under different greenhouse cultivation conditions and under elevated UV-B illumination. Microscope analyses of leaves grown under optimized conditions revealed significant differences both in cell structure and size when the transgenic VHb lines were compared with the control lines. VHb lines displayed a higher relative volume of mitochondria and a significantly enhanced accumulation of starch in chloroplasts, all of which pointed towards changes in cellular energy production. Under elevated UV-B illumination, the differences between VHb lines became evident. Some specific VHb lines had elevated levels of total flavonoids, individual quercetin, kaempferol- and myricetin-derivatives relative to controls and other transgenic lines. This observation may reflect the availability of extra energy resources for secondary metabolite production and possibly an enhanced protection ability of these transgenic lines against UV-B illumination. Thus, all these findings point to changes in the energy metabolism of VHb lines. In the cultivation conditions tested this observation did not, however, result in a general improvement of elongation growth.

Journal Article↗

PubMed2003

Expression of mercuric ion reductase in Eastern cottonwood (Populus deltoides) confers mercuric ion reduction and resistance.

Mercury is one of the most hazardous heavy metals and is a particular problem in aquatic ecosystems, where organic mercury is biomagnified in the food chain. Previous studies demonstrated that transgenic model plants expressing a modified mercuric ion reductase gene from bacteria could detoxify mercury by converting the more toxic and reductive ionic form [Hg(II)] to less toxic elemental mercury [Hg(0)]. To further investigate if a genetic engineering approach for mercury phytoremediation can be effective in trees with a greater potential in riparian ecosystems, we generated transgenic Eastern cottonwood (Populus deltoides) trees expressing modified merA9 and merA18 genes. Leaf sections from transgenic plantlets produced adventitious shoots in the presence of 50 microm Hg(II) supplied as HgCl2, which inhibited shoot induction from leaf explants of wild-type plantlets. Transgenic shoots cultured in a medium containing 25 microm Hg(II) showed normal growth and rooted, while wild-type shoots were killed. When the transgenic cottonwood plantlets were exposed to Hg(II), they evolved 2-4-fold the amount of Hg(0) relative to wild-type plantlets. Transgenic merA9 and merA18 plants accumulated significantly higher biomass than control plants on a Georgia Piedmont soil contaminated with 40 p.p.m. Hg(II). Our results indicate that Eastern cottonwood plants expressing the bacterial mercuric ion reductase gene have potential as candidates for in situ remediation of mercury-contaminated soils or wastewater.

Journal Article↗

PubMed2000

Biochemical model reactions indicative of inflammatory processes. Activities of extracts from Fraxinus excelsior and Populus tremula.

All processes of oxygen activation include very reactive intermediates. Therefore, aerobic cells must cope with--and to some extent also adapt to--oxidative stress provoked for example by infections or intoxications, where these reactive intermediates accumulate. All inflammatory processes include such oxygen activating processes where reactive oxygen species (ROS) are produced. Dependent on the strength of these impact(s), several symptoms indicate the deviation from normal, steady-state metabolism. Intrinsic radical scavenging processes or compounds administered with food thus have to warrant metabolic control within certain limits. Antioxidants which in many cases are free radical scavengers or quenchers of activated states comprise a vast number of classes of organic molecules including phenolics as the most prominent ones. In this publication the activities of extracts from Fraxinus excelsior, Populus tremula and Solidago virgaurea as components of the drug Phytodolor and their mechanisms of protection from oxidative damage are summarized. In addition, new results on tyrosine nitration, a process characteristic for sites of inflammation, and its inhibition by these plant extracts, is reported.

Animals↗

PubMed1998

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 distinct 4CL genes, Pt4CL1 and Pt4CL2 (63% protein sequence identity), that are differentially expressed in aspen (Populus tremuloides). The Escherichia coli-expressed and purified Pt4CL1 and Pt4CL2 proteins exhibited highly divergent substrate preference as well as specificity that reveal the association of Pt4CL1 with the biosynthesis of guaiacyl-syringyl lignin and the involvement of Pt4CL2 with other phenylpropanoid formation. Northern hybridization analysis demonstrated that Pt4CL1 mRNA is specifically expressed in lignifying xylem tissues and Pt4CL2 mRNA is specifically expressed in epidermal layers in the stem and the leaf, consistent with the promoter activities of Pt4CL1 and Pt4CL2 genes based on the heterologous promoter-beta-glucouronidase fusion analysis. Thus, the expression of Pt4CL1 and Pt4CL2 genes is compartmentalized to regulate the differential formation of phenylpropanoids that confer different physiological functions in aspen; Pt4CL1 is devoted to lignin biosynthesis in developing xylem tissues, whereas Pt4CL2 is involved in the biosynthesis of other phenolics, such as flavonoids, in epidermal cells.

Amino Acid Sequence↗

PubMed1997

Expression of chloroplastic genes during autumnal senescence in a deciduous tree Populus deltiodes.

In Populus deltoides, a deciduous tree, the development on new leaves starts in the month of March, the leaves reach maturity by October and fall by December. Changes in the composition and function of the photosynthetic apparatus were analysed during autumnal senescence. With the progress of senescence, there was an initial increase followed by a decrease in the steady state levels of psbA, psbD/C and psaA/B gene transcripts. Decrease in the steady state level of D1 protein was faster than that of Cytochrome f. The decline in LHCP level was seen only during late senescence. Although the leaves continue to look green and healthy till late November, the electron transport driven by individual photosystems started declining by October end suggesting the onset of senescence.

Blotting, Northern↗

PubMed2000

Leaves of Salicaceae (Salix and Populus) from Oligocene Sediments Near Tepexi de Rodríguez, Puebla, Mexico.

Eleven new salicaceous taxa based on fossil leaves, seven Salix and four Populus species, are described from the Oligocene Los Ahuehuetes locality, Pie de Vaca Formation, near Tepexi de Rodríguez in Puebla, Mexico. They are characterized by the presence of typical salicoid teeth, camptodromous secondary venation, and elliptic or lanceolate shape. Morphological differences between these new fossil plants and those reported previously from the United States and elsewhere indicate that diversification among these taxa occurred early during their differentiation. Furthermore, the limited morphological similarities of the fossil and extant plants growing naturally in Mexico also indicate a high rate of evolution. Documenting the expansion of high-latitude North American taxa into lower latitudes at the time of deposition of the Pie de Vaca Formation confirms that at least some of the typical boreal taxa were part of dry tropical communities in low-latitude North America and underscores the need to reevaluate the origin of this southern vegetation.

Journal Article↗