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  • Plant physiology
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  • 1
    Language: English
    In: Plant physiology, November 2012, Vol.160(3), pp.1515-29
    Description: Understanding seasonality and longevity is a major challenge in tree biology. In woody species, growth phases and dormancy follow one another consecutively. In the oldest living individuals, the annual cycle may run for more than 1,000 years. So far, however, not much is known about the processes triggering reactivation from dormancy. In this study, we focused on wood rays, which are known to play an important role in tree development. The transition phase from dormancy to flowering in early spring was compared with the phase of active growth in summer. Rays from wood samples of poplar (Populus × canescens) were enriched by laser microdissection, and transcripts were monitored by poplar whole-genome microarrays. The resulting seasonally varying complex expression and metabolite patterns were subjected to pathway analyses. In February, the metabolic pathways related to flower induction were high, indicating that reactivation from dormancy was already taking place at this time of the year. In July, the pathways related to active growth, like lignin biosynthesis, nitrogen assimilation, and defense, were enriched. Based on "marker" genes identified in our pathway analyses, we were able to validate periodical changes in wood samples by quantitative polymerase chain reaction. These studies, and the resulting ray database, provide new insights into the steps underlying the seasonality of poplar trees.
    Keywords: Seasons ; Populus -- Cytology ; Trees -- Physiology ; Wood -- Cytology
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 2
    Language: English
    In: Plant Physiology, 1 November 1983, Vol.73(3), pp.560-565
    Description: In the presence of excess sulfate, cysteine synthesis in pumpkin (Cucurbita pepo) leaves is not limited by sulfate reduction, but by the availability of O-acetylserine. Feeding of O-acetylserine or its metabolic precursors S-acetyl-coenzyme-A and coenzyme A to leaf discs enhanced the incorportion of [ 35 S]sulfate into reduced sulfur compounds, mainly into cysteine, at the cost of lowered H 2 S emission; the uptake and reduction of sulfate is not affected by these treatments. β-Fluoropyruvate, an inhibitor of the generation of S-acetyl-coenzyme A via pyruvate dehydrogenase, stimulated H 2 S emission in response to sulfate. This stimulation is overcompensated by addition of O-acetylserine, S-acetyl-coenzyme A, or coenzyme A. These results indicate that, in the presence of high amounts of sulfate, excess sulfur is reduced and emitted as H 2 S into the atmosphere. The H 2 S emitted seems to be produced by liberation from a precursor of cysteine rather than by cysteine desulfhydration.
    Keywords: Physical sciences -- Chemistry -- Chemical compounds ; Physical sciences -- Chemistry -- Chemical elements ; Biological sciences -- Biochemistry -- Metabolism ; Physical sciences -- Physics -- Microphysics ; Environmental studies -- Environmental quality -- Environmental degradation ; Biological sciences -- Biology -- Botany ; Physical sciences -- Chemistry -- Chemical compounds ; Biological sciences -- Biology -- Physiology ; Physical sciences -- Physics -- Matter ; Physical sciences -- Physics -- Fundamental forces
    ISSN: 00320889
    E-ISSN: 15322548
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  • 3
    Language: English
    In: Plant physiology, June 2017, Vol.174(2), pp.798-814
    Description: Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants () were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter () expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, At, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of , a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.
    Keywords: Abscisic Acid -- Biosynthesis ; Arabidopsis Proteins -- Metabolism ; Organic Anion Transporters -- Metabolism ; Plant Stomata -- Physiology ; Sulfates -- Metabolism ; Xylem -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 4
    Language: English
    In: Plant physiology, September 2015, Vol.169(1), pp.560-75
    Description: Isoprene emissions from poplar (Populus spp.) plantations can influence atmospheric chemistry and regional climate. These emissions respond strongly to temperature, [CO2], and drought, but the superimposed effect of these three climate change factors are, for the most part, unknown. Performing predicted climate change scenario simulations (periodic and chronic heat and drought spells [HDSs] applied under elevated [CO2]), we analyzed volatile organic compound emissions, photosynthetic performance, leaf growth, and overall carbon (C) gain of poplar genotypes emitting (IE) and nonemitting (NE) isoprene. We aimed (1) to evaluate the proposed beneficial effect of isoprene emission on plant stress mitigation and recovery capacity and (2) to estimate the cumulative net C gain under the projected future climate. During HDSs, the chloroplastidic electron transport rate of NE plants became impaired, while IE plants maintained high values similar to unstressed controls. During recovery from HDS episodes, IE plants reached higher daily net CO2 assimilation rates compared with NE genotypes. Irrespective of the genotype, plants undergoing chronic HDSs showed the lowest cumulative C gain. Under control conditions simulating ambient [CO2], the C gain was lower in the IE plants than in the NE plants. In summary, the data on the overall C gain and plant growth suggest that the beneficial function of isoprene emission in poplar might be of minor importance to mitigate predicted short-term climate extremes under elevated [CO2]. Moreover, we demonstrate that an analysis of the canopy-scale dynamics of isoprene emission and photosynthetic performance under multiple stresses is essential to understand the overall performance under proposed future conditions.
    Keywords: Climate Change ; Butadienes -- Analysis ; Hemiterpenes -- Analysis ; Pentanes -- Analysis ; Populus -- Chemistry
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 5
    Language: English
    In: Plant physiology, May 2004, Vol.135(1), pp.152-60
    Description: This study was performed to test if alternative carbon sources besides recently photosynthetically fixed CO2 are used for isoprene formation in the leaves of young poplar (Populus x canescens) trees. In a 13CO2 atmosphere under steady state conditions, only about 75% of isoprene became 13C labeled within minutes. A considerable part of the unlabeled carbon may be derived from xylem transported carbohydrates, as may be shown by feeding leaves with [U-13C]Glc. As a consequence of this treatment approximately 8% to 10% of the carbon emitted as isoprene was 13C labeled. In order to identify further carbon sources, poplar leaves were depleted of leaf internal carbon pools and the carbon pools were refilled with 13C labeled carbon by exposure to 13CO2. Results from this treatment showed that about 30% of isoprene carbon became 13C labeled, clearly suggesting that, in addition to xylem transported carbon and CO2, leaf internal carbon pools, e.g. starch, are used for isoprene formation. This use was even increased when net assimilation was reduced, for example by abscisic acid application. The data provide clear evidence of a dynamic exchange of carbon between different cellular precursors for isoprene biosynthesis, and an increasing importance of these alternative carbon pools under conditions of limited photosynthesis. Feeding [1,2-13C]Glc and [3-13C]Glc to leaves via the xylem suggested that alternative carbon sources are probably derived from cytosolic pyruvate/phosphoenolpyruvate equivalents and incorporated into isoprene according to the predicted cleavage of the 3-C position of pyruvate during the initial step of the plastidic deoxyxylulose-5-phosphate pathway.
    Keywords: Carbon -- Pharmacology ; Carbon Dioxide -- Pharmacology ; Hemiterpenes -- Biosynthesis ; Plant Leaves -- Metabolism ; Populus -- Metabolism
    ISSN: 0032-0889
    E-ISSN: 15322548
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  • 6
    Language: English
    In: Plant physiology, August 2004, Vol.135(4), pp.1967-75
    Description: In this study, we investigated the prompt release of acetaldehyde and other oxygenated volatile organic compounds (VOCs) from leaves of Grey poplar [Populus x canescens (Aiton) Smith] following light-dark transitions. Mass scans utilizing the extremely fast and sensitive proton transfer reaction-mass spectrometry technique revealed the following temporal pattern after light-dark transitions: hexenal was emitted first, followed by acetaldehyde and other C(6)-VOCs. Under anoxic conditions, acetaldehyde was the only compound released after switching off the light. This clearly indicated that hexenal and other C(6)-VOCs were released from the lipoxygenase reaction taking place during light-dark transitions under aerobic conditions. Experiments with enzyme inhibitors that artificially increased cytosolic pyruvate demonstrated that the acetaldehyde burst after light-dark transition could not be explained by the recently suggested pyruvate overflow mechanism. The simulation of light fleck situations in the canopy by exposing leaves to alternating light-dark and dark-light transitions or fast changes from high to low photosynthetic photon flux density showed that this process is of minor importance for acetaldehyde emission into the Earth's atmosphere.
    Keywords: Light ; Acetaldehyde -- Metabolism ; Organic Chemicals -- Metabolism ; Plant Leaves -- Metabolism ; Populus -- Metabolism
    ISSN: 0032-0889
    E-ISSN: 15322548
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  • 7
    Language: English
    In: Plant physiology, November 2002, Vol.130(3), pp.1406-13
    Description: Cysteine synthesis from sulfide and O-acetyl-L-serine (OAS) is a reaction interconnecting sulfate, nitrogen, and carbon assimilation. Using Lemna minor, we analyzed the effects of omission of CO(2) from the atmosphere and simultaneous application of alternative carbon sources on adenosine 5'-phosphosulfate reductase (APR) and nitrate reductase (NR), the key enzymes of sulfate and nitrate assimilation, respectively. Incubation in air without CO(2) led to severe decrease in APR and NR activities and mRNA levels, but ribulose-1,5-bisphosphate carboxylase/oxygenase was not considerably affected. Simultaneous addition of sucrose (Suc) prevented the reduction in enzyme activities, but not in mRNA levels. OAS, a known regulator of sulfate assimilation, could also attenuate the effect of missing CO(2) on APR, but did not affect NR. When the plants were subjected to normal air after a 24-h pretreatment in air without CO(2), APR and NR activities and mRNA levels recovered within the next 24 h. The addition of Suc and glucose in air without CO(2) also recovered both enzyme activities, with OAS again influenced only APR. (35)SO(4)(2-) feeding showed that treatment in air without CO(2) severely inhibited sulfate uptake and the flux through sulfate assimilation. After a resupply of normal air or the addition of Suc, incorporation of (35)S into proteins and glutathione greatly increased. OAS treatment resulted in high labeling of cysteine; the incorporation of (35)S in proteins and glutathione was much less increased compared with treatment with normal air or Suc. These results corroborate the tight interconnection of sulfate, nitrate, and carbon assimilation.
    Keywords: Oxidoreductases Acting on Sulfur Group Donors ; Araceae -- Metabolism ; Carbon -- Metabolism ; Nitrogen -- Metabolism ; Sulfates -- Metabolism
    ISSN: 0032-0889
    E-ISSN: 15322548
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  • 8
    Language: English
    In: Plant Physiology, 1 November 1996, Vol.112(3), pp.1071-1078
    Description: Internode stem fragments of the poplar hybrid Populus tremula × Populus alba were transformed with a bacterial gene (gshI) for γ-glutamylcysteine synthetase (γ-ECS) targeted to the cytosol. Lines overexpressing γ-ECS were identified by northern analysis, and the transformant with the highest enzyme activity was used to investigate the control of glutathione synthesis. Whereas foliar γ-ECS activity was below the limit of detection in untransformed plants, activities of up to 8.7 nmol mg -1 protein min -1 were found in the transformant, in which the foliar contents of γ-glutamylcysteine (γ-EC) and glutathione were increased approximately 10- and 3-fold, respectively, without affecting either the reduction state of the glutathione pool or the foliar cysteine content. A supply of exogenous cysteine to leaf discs increased the glutathione content from both transformed and untransformed poplars, and caused the γ-EC content of the transformant discs to increase still further. The following conclusions are drawn: (a) the native γ-ECS of untransformed poplars exists in quantities that are limiting for foliar glutathione synthesis; (b) foliar glutathione synthesis in untransformed poplars is limited by cysteine availability; (c) in the transformant interactions between glutathione synthesis and cysteine synthesis operate to sustain the increased formation of γ-EC and glutathione; and (d) the foliar glutathione content of the transformant is restricted by cysteine availability and by the activity of glutathione synthetase.
    Keywords: Biological sciences -- Biology -- Botany ; Physical sciences -- Chemistry -- Chemical compounds ; Biological sciences -- Biology -- Botany ; Physical sciences -- Chemistry -- Chemical compounds ; Physical sciences -- Chemistry -- Chemical elements ; Biological sciences -- Biology -- Genetics ; Physical sciences -- Chemistry -- Chemical compounds ; Physical sciences -- Chemistry -- Chemical compounds ; Physical sciences -- Physics -- Mechanics ; Biological sciences -- Biology -- Cytology
    ISSN: 00320889
    E-ISSN: 15322548
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  • 9
    Language: English
    In: Plant physiology, December 2009, Vol.151(4), pp.2110-9
    Description: The consequences of altered abscisic acid (ABA) sensitivity in gray poplar (Populus x canescens [Ait.] Sm.) development were examined by ectopic expression of the Arabidopsis (Arabidopsis thaliana) mutant abi1 (for abscisic acid insensitive1) gene. The expression resulted in an ABA-insensitive phenotype revealed by a strong tendency of abi1 poplars to wilt, impaired responsiveness of their stomata to ABA, and an ABA-resistant bud outgrowth. These plants therefore required cultivation under very humid conditions to prevent drought stress symptoms. Morphological alterations became evident when comparing abi1 poplars with poplars expressing Arabidopsis nonmutant ABI1 or wild-type plants. abi1 poplars showed increased stomatal size, enhanced shoot growth, and retarded leaf and root development. The increased stomatal size and its reversion to the size of wild-type plants by exogenous ABA indicate a role for ABA in regulating stomatal development. Enhanced shoot growth and retarded leaf and root development support the hypothesis that ABA acts independently from drought stress as a negative regulator of growth in shoots and as a positive regulator of growth in leaves and roots. In shoots, we observed an interaction of ABA with ethylene: abi1 poplars exhibited elevated ethylene production, and the ethylene perception inhibitor Ag(+) antagonized the enhanced shoot growth. Thus, we provide evidence that ABA acts as negative regulator of shoot growth in nonstressed poplars by restricting ethylene production. Furthermore, we show that ABA has a role in regulating shoot branching by inhibiting lateral bud outgrowth.
    Keywords: Abscisic Acid -- Pharmacology ; Arabidopsis -- Genetics ; Arabidopsis Proteins -- Genetics ; Mutation -- Genetics ; Phosphoprotein Phosphatases -- Genetics ; Plant Stomata -- Growth & Development ; Populus -- Genetics
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 10
    Language: English
    In: Plant physiology, December 2009, Vol.151(4), pp.1902-17
    Description: Ectomycorrhizas (EMs) alleviate stress tolerance of host plants, but the underlying molecular mechanisms are unknown. To elucidate the basis of EM-induced physiological changes and their involvement in stress adaptation, we investigated metabolic and transcriptional profiles in EM and non-EM roots of gray poplar (Populus x canescens) in the presence and absence of osmotic stress imposed by excess salinity. Colonization with the ectomycorrhizal fungus Paxillus involutus increased root cell volumes, a response associated with carbohydrate accumulation. The stress-related hormones abscisic acid and salicylic acid were increased, whereas jasmonic acid and auxin were decreased in EM compared with non-EM roots. Auxin-responsive reporter plants showed that auxin decreased in the vascular system. The phytohormone changes in EMs are in contrast to those in arbuscular mycorrhizas, suggesting that EMs and arbuscular mycorrhizas recruit different signaling pathways to influence plant stress responses. Transcriptome analyses on a whole genome poplar microarray revealed activation of genes related to abiotic and biotic stress responses as well as of genes involved in vesicle trafficking and suppression of auxin-related pathways. Comparative transcriptome analysis indicated EM-related genes whose transcript abundances were independent of salt stress and a set of salt stress-related genes that were common to EM non-salt-stressed and non-EM salt-stressed plants. Salt-exposed EM roots showed stronger accumulation of myoinositol, abscisic acid, and salicylic acid and higher K(+)-to-Na(+) ratio than stressed non-EM roots. In conclusion, EMs activated stress-related genes and signaling pathways, apparently leading to priming of pathways conferring abiotic stress tolerance.
    Keywords: Gene Expression Profiling ; Adaptation, Physiological -- Genetics ; Metabolome -- Genetics ; Mycorrhizae -- Physiology ; Plant Roots -- Physiology ; Populus -- Genetics ; Stress, Physiological -- Genetics
    ISSN: 00320889
    E-ISSN: 1532-2548
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