Biomedical subjects

Heinz Rennenberg

Publications and source records attributed to Heinz Rennenberg.

At least 19 recordsLinked to original sources

PubMed2007

Assessing environmental and physiological controls over water relations in a Scots pine (Pinus sylvestris L.) stand through analyses of stable isotope composition of water and organic matter.

This study investigated the influence of meteorological, pedospheric and physiological factors on the water relations of Scots pine, as characterized by the origin of water taken up, by xylem transport as well as by carbon isotope discrimination (Delta13C) and oxygen isotope enrichment (Delta18O) of newly assimilated organic matter. For more than 1 year, we quantified delta2H and delta18O of potential water sources and xylem water as well as Delta13C and Delta18O in twig and trunk phloem organic matter biweekly, and related these values to continuously measured or modelled meteorological parameters, soil water content, stand transpiration (ST) and canopy stomatal conductance (G(s)). During the growing season, delta18O and delta2H of xylem water were generally in a range comparable to soil water from a depth of 2-20 cm. Long residence time of water in the tracheids uncoupled the isotopic signals of xylem and soil water in winter. Delta18O but not Delta13C in phloem organic matter was directly indicative of recent environmental conditions during the whole year. Delta18O could be described applying a model that included 18O fractionation associated with water exchange between leaf and atmosphere, and with the production of organic matter as well as the influence of transpiration. Phloem Delta13C was assumed to be concertedly influenced by G(s) and photosynthetically active radiation (PAR) (as a proxy for photosynthetic capacity). We conclude that isotope signatures can be used as effective tools (1) to characterize the seasonal dynamics in source and xylem water, and (2) to assess environmental effects on transpiration and G(s) of Scots pine, thus helping to understand and predict potential impacts of climate change on trees and forest ecosystems.

Carbon Isotopes↗

PubMed2006

Plant sulfite oxidase as novel producer of H2O2: combination of enzyme catalysis with a subsequent non-enzymatic reaction step.

Sulfite oxidase (EC 1.8.3.1) from the plant Arabidopsis thaliana is the smallest eukaryotic molybdenum enzyme consisting of a molybdenum cofactor-binding domain but lacking the heme domain that is known from vertebrate sulfite oxidase. While vertebrate sulfite oxidase is a mitochondrial enzyme with cytochrome c as the physiological electron acceptor, plant sulfite oxidase is localized in peroxisomes and does not react with cytochrome c. Here we describe results that identified oxygen as the terminal electron acceptor for plant sulfite oxidase and hydrogen peroxide as the product of this reaction in addition to sulfate. The latter finding might explain the peroxisomal localization of plant sulfite oxidase. 18O labeling experiments and the use of catalase provided evidence that plant sulfite oxidase combines its catalytic reaction with a subsequent non-enzymatic step where its reaction product hydrogen peroxide oxidizes another molecule of sulfite. In vitro, for each catalytic cycle plant SO will bring about the oxidation of two molecules of sulfite by one molecule of oxygen. In the plant, sulfite oxidase could be responsible for removing sulfite as a toxic metabolite, which might represent a means to protect the cell against excess of sulfite derived from SO2 gas in the atmosphere (acid rain) or during the decomposition of sulfur-containing amino acids. Finally we present a model for the metabolic interaction between sulfite and catalase in the peroxisome.

Acid Rain↗

PubMed2006

Exogenous supply of glutamine and active cytokinin to the roots reduces NO3- uptake rates in poplar.

The present study shows for the first time the influence of exogenously applied amino acids and cytokinin on the physiological and molecular aspects of N metabolism in poplar trees. In a short-term feeding experiment, glutamine or trans-zeatin riboside (tZR) was added directly to the nutrient solution. NO3- net uptake declined significantly in response to both treatments. Feeding with glutamine brought about an increase in concentrations of different amino compounds in the roots (glutamine, glutamate, alanine, gamma-amino butyric acid (GABA) and NH4+, which negatively correlated with the net NO3- uptake. The plants showed a reduction of cytosolic glutamine synthetase 1 (GS1) transcript level in the roots. In addition, glutamine feeding changed the root-to-shoot distribution on N assimilation in favour of the leaves and plant internal N cycling. tZR treatment resulted in expansion of zeatin-type (Z-type) cytokinins in the roots and increased nitrate reductase (NR)-mRNA level. The results indicate that both particular amino acids and active cytokinins are involved in the feedback regulation of N uptake and metabolism in poplar. We propose that inhibition of N uptake by cytokinins in poplar is more complex than that mediated by amino compounds, and other effectors are involved in this regulation.

Cytokinins↗

PubMed2006

Carbon isotopic composition and oxygen isotopic enrichment in phloem and total leaf organic matter of European beech (Fagus sylvatica L.) along a climate gradient.

This study investigated the influence of climate on the carbon isotopic composition (sigma13C) and oxygen isotopic enrichment (delta18O) above the source water of different organic matter pools in European beech. In July and September 2002, sigma13C and delta18O were determined in phloem carbohydrates and in bulk foliage of adult beech trees along a transect from central Germany to southern France, where beech reaches its southernmost distributional limit. The data were related to meteorological and physiological parameters. The climate along the transect stretches from temperate [subcontinental (SC)] to submediterranean (SM). Both sigma13Cleaf and delta18Oleaf were representative of site-specific long-term environmental conditions. sigma13C of leaves collected in September was indicative of stomatal conductance, vapour pressure deficit (VPD) and radiation availability of the current growing season. delta18O was mainly correlated to mean growing season relative humidity (RH) and VPD. In contrast to the leaves, sigma13Cphloem varied considerably between July and September and was well correlated with canopy stomatal conductance (Gs) in a 2 d integral prior to phloem sampling. The relationship between sigma13C and delta18O in both leaves and phloem sap points, however, to a combined influence of stomatal conductance and photosynthetic capacity on the variation of sigma13C along the transect. delta18Ophloem could be described by applying a model that included 18O fractionation associated with water exchange between the leaf and the atmosphere and with the production of organic matter. Hence, isotope signatures can be used as effective tools to assess the water balance of beech, and thus, help predict the effects of climatic change on one of the ecologically and economically most important tree species in Central Europe.

Carbon Isotopes↗

PubMed2005

Impact of short-term and long-term elevated CO2 on emission of carbonyls from adult Quercus petraea and Carpinus betulus trees.

The study aimed to elucidate the effect of elevated CO2 in short- and long-term experiments on the emission potential of carbonyls from mature oak (Quercus petraea) and hornbeam (Carpinus betulus). The trees were investigated using a canopy crane established in a mixed forest in Switzerland. Short-term CO2 experiments were performed on single leaves with a gas exchange measuring unit by increasing CO2 in the enclosure before and during the measurements. Long-term CO2 fumigation was performed for one vegetation period by a webFACE design. Short-term as well as long-term exposure of leaves resulted in no significant changes in carbonyl exchange in neither Q. petraea nor C. betulus. Carbonyl emission was not affected by stomatal closure under elevated CO2 levels. In contrast to the emission of isoprenoids from vegetation which is thought to be reduced at elevated atmospheric CO2, the exchange of carbonyls seems to be generally unaffected under these conditions.

Acetaldehyde↗

PubMed2005

Expression profiling of metabolic genes in response to methyl jasmonate reveals regulation of genes of primary and secondary sulfur-related pathways in Arabidopsis thaliana.

The treatment of Arabidopsis thaliana with methyl jasmonate was used to investigate the reaction of 2467 selected genes of primary and secondary metabolism by macroarray hybridization. Hierarchical cluster analysis allowed distinctions to be made between diurnally and methyl jasmonate regulated genes in a time course from 30 min to 24 h. 97 and 64 genes were identified that were up- or down-regulated more than 2-fold by methyl jasmonate, respectively. These genes belong to 18 functional categories of which sulfur-related genes were by far strongest affected. Gene expression and metabolite patterns of sulfur metabolism were analysed in detail, since numerous defense compounds contain oxidized or reduced sulfur. Genes encoding key reactions of sulfate reduction as well as of cysteine, methionine and glutathione synthesis were rapidly up-regulated, but none of the known sulfur-deficiency induced sulfate transporter genes. In addition, increased expression of genes of sulfur-rich defense proteins and of enzymes involved in glucosinolate metabolism was observed. In contrast, profiling of primary and secondary sulfur metabolites revealed only an increase in the indole glucosinolate glucobrassicin upon methyl jasmonate treatment. The observed rapid mRNA changes were thus regulated by a signal independent of the known sulfur deficiency response. These results document for the first time how comprehensively the regulation of sulfur-related genes and plant defense are connected. This interaction is discussed as a new approach to differentiate between supply- and demand-driven regulation of the sulfate assimilation pathway.

Acetates↗

PubMed2005

Seasonal patterns of ascorbate in the needles of Scots Pine (Pinus sylvestris L.) trees: correlation analyses with atmospheric O3 and NO2 gas mixing ratios and meteorological parameters.

In the present field study the role of ascorbate in scavenging the harmful atmospheric trace gases O3 and NO2 was examined. For this purpose ascorbate contents were determined in needles of adult Scots pine trees (Pinus sylvestris L.) during three consecutive years. Ascorbate contents were correlated with ambient tropospheric O3 and NO2 concentrations and with meteorological parameters. The results showed a strong correlation of atmospheric O3 but not of atmospheric NO2 concentrations with the apoplastic content of ascorbate during the seasonal course. Ascorbate contents in needle extracts did not correlate with ambient trace gas concentrations. In the apoplastic space, but not in needle extracts ascorbate contents correlate highly significantly with global radiation. From these results it is assumed that apoplastic ascorbate in Scots pine needles is adapted to the actual atmospheric O3 concentration to mediate immediate detoxification of O3, while the atmospheric O3 concentration itself is largely dependent on light intensity.

Air Pollutants↗

PubMed2005

Ability of transgenic poplars with elevated glutathione content to tolerate zinc(2+) stress.

Phytoremediation potentials of four poplar lines, Populus nigra (N-SL clone), Populus canescens, and two transgenic P. canescens clones were investigated using in vitro leaf discs cultures. The transgenic poplars overexpressed a bacterial gene encoding gamma-glutamylcysteine synthetase in the cytosol (11ggs) or in the chlopoplasts (6LgI), and therefore, they contained an elevated level of glutathione. Leaf discs of poplar clones were exposed to different concentrations of ZnSO(4) for 21 days. Zinc(2+) was phytotoxic only at high concentrations (10(-2) to 10(-1) M) at all P. canescens lines, but P. nigra was more sensitive. Transgenic poplars showed elevated heavy metal uptake as compared to the nontransformed clones. Treatments with zinc(2+) strongly induced the activity of glutathione S-transferase enzyme in untransformed poplar lines but to a lesser extent in the transgenic clones. These results suggest that transgenic poplars are more suitable for phytoremediation of soils contaminated with zinc(2+) than wild-type plants.

Adaptation, Physiological↗

PubMed2005

Effects of elevated pCO2 and/or pO3 on C-, N-, and S-metabolites in the leaves of juvenile beech and spruce differ between trees grown in monoculture and mixed culture.

Three and four-year-old saplings of beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) grown in monoculture and mixed culture were exposed in phytotrons to (1) ambient air, (2) elevated pO(3), (3) elevated pCO(2), or (4) elevated pCO(2) plus elevated pO(3). After 5 months, the contents of soluble sugars, starch, soluble amino compounds, non-structural proteins (NSP), as well as reduced (GSH) and oxidized (GSSG) glutathione were determined in the leaves of both species in order to assess the effects of the gaseous regimes on primary metabolism. Elevated pO(3) did not affect sugar and starch levels in beech leaves in monoculture, but significantly increased sugar levels in beech leaves grown in mixed culture. In spruce needles, sugar levels tended to be enhanced in both culture types. Individual and combined exposure of elevated pCO(2) led to an increase in non-structural carbohydrate (soluble sugars plus starch) levels in beech and spruce leaves of both culture types. Differences in the responses of non-structural carbohydrate levels to elevated pCO(2) between beech and spruce were apparent from different contributions of sugars and starch to the increase in carbohydrate levels. Exposure to elevated pCO(2) and/or elevated pO(3) did not affect the levels of soluble amino compounds and NSP in beech leaves, but reduced amino compound levels in spruce needles of both culture types. Elevated pO(3) increased GSH levels in the leaves of both tree species in both culture types, while GSSG levels in monoculture were reduced in beech leaves, but significantly enhanced in spruce needles. Elevated pCO(2) reduced GSSG levels in beech and spruce leaves in monoculture, and GSH levels in spruce needles of both culture types. The combination of elevated pCO(2) and pO(3) increased GSSG levels in beech leaves of both culture types and in spruce needles in monoculture, but reduced GSH levels in spruce needles of both culture types. Apparently, under each gaseous regime, the culture type significantly altered primary metabolism of the leaves of beech and spruce.

Carbohydrate Metabolism↗

PubMed2005

Phytoremediation.

Explore the source record for details and available documents.

Biodegradation, Environmental↗

PubMed2005

Irradiance and temperature affect the competitive interference of blackberry on the physiology of European beech seedlings.

The potential negative influence of competition from early successional species like blackberry (Rubus fruticosus) may be decisive for the natural regeneration success of drought-sensitive beech (Fagus sylvatica), especially in the light of climate change. With a split plot glasshouse experiment, we investigated the influence of two air temperature and irradiance levels on the competitive interference of blackberry on the water, nitrogen (N) and carbon (C) balance of beech seedlings under moderate drought. When increased temperature was accompanied by low irradiance the biomass, root-to-shoot ratio, N uptake and assimilation rates of blackberry were lower compared with beech, either grown alone or with blackberry. By contrast, when elevated temperature and high irradiance were combined, the root-to-shoot ratio and specific N uptake rate of blackberry were substantially increased, while the N acquisition of beech was impaired. Under lower temperature, with either full light or shade, the presence of blackberry had no significant effects on beech, for almost all tested parameters. Under elevated air temperature beech was impaired by the presence of blackberry at high irradiance. These findings emphasize the interacting effects between environmental factors and competition on the establishment of beech regeneration, which should be considered for future forest management in the frame of climate change.

Fagus↗

PubMed2005

Does glutathione metabolism have a role in the defence of poplar against zinc excess?

Transition metals such as zinc (Zn) are essential micronutrients for many physiological processes, but they become toxic at elevated levels. Zinc is one of the most abundant trace heavy metals present in agro-ecosystems. Populus spp. have been suggested as good candidates for using to study the removal and/or immobilization of environmental organic and inorganic pollutants. In order to understand the physiological and biochemical bases of this assumption for Zn, plants of Populus deltoides x P. nigra (P. x euramericana) were grown in hydroponics with different concentrations of Zn [1 microm (control), and 1, 5 and 10 mm] in the nutrient solution.Shoot biomass decreased at 5 and 10 mm Zn, while the Zn content of young leaves increased progressively with increasing Zn concentration (1-10 mm). Total glutathione (GSH+GSSG) content was reduced with increasing Zn concentration, while the contribution of oxidized to total glutathione increased. Despite these observations, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that the gene expression of GSH reductase (GR, chloroplastic and cytosolic isoform) and gamma-glutamylcysteine synthetase (gamma-ECS) increased in young leaves of poplars treated with excess Zn. We conclude that GSH synthesis, consumption and redox status play a central role in the response of poplars to high concentrations of Zn.

Crosses, Genetic↗

PubMed2004

Transient release of oxygenated volatile organic compounds during light-dark transitions in Grey poplar leaves.

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.

Acetaldehyde↗

PubMed2004

Control of sulphate assimilation and glutathione synthesis: interaction with N and C metabolism.

Sulphate assimilation is an essential pathway being a source of reduced sulphur for various cellular processes and for the synthesis of glutathione, a major factor in plant stress defence. Many reports have shown that sulphate assimilation is well co-ordinated with the assimilation of nitrate and carbon. It has long been known that, during nitrate deficiency, sulphate assimilation is reduced and that the capacity to reduce nitrate is diminished in plants starved for sulphate. Only recently, however, was it shown that adenosine 5' phosphosulphate reductase (APR), the key enzyme of sulphate assimilation, is regulated by carbohydrates. In plants treated with sucrose or glucose APR was induced, whereas the activity was strongly reduced in plants grown in CO(2)-free air. The availability of cysteine is a crucial factor in glutathione synthesis, but an adequate supply of glutamate and glycine are also important. The molecular mechanisms for the co-ordination of S, N, and C assimilation are not known. O-acetylserine, a precursor of cysteine, was proposed to be the signal regulating sulphate assimilation, but most probably is not the outgoing signal to N and C metabolism. cDNA arrays revealed the induction of genes involved in auxin synthesis upon S-starvation, pointing to a possible role of phytohormones. Clearly, despite significant progress in understanding the regulation of sulphate assimilation and glutathione synthesis, their co-ordination with N and C metabolism achieved, and several potential signal molecules identified, present knowledge is still far from being sufficient.

Carbon↗

PubMed2004

Contribution of different carbon sources to isoprene biosynthesis in poplar leaves.

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.

Biological Transport↗

PubMed2004

Regulation of sulphate assimilation by glutathione in poplars (Populus tremula x P. alba) of wild type and overexpressing gamma-glutamylcysteine synthetase in the cytosol.

Glutathione (GSH) is the major low molecular weight thiol in plants with different functions in stress defence and the transport and storage of sulphur. Its synthesis is dependent on the supply of its constituent amino acids cysteine, glutamate, and glycine. GSH is a feedback inhibitor of the sulphate assimilation pathway, the primary source of cysteine synthesis. Sulphate assimilation has been analysed in transgenic poplars (Populus tremula x P. alba) overexpressing gamma-glutamylcysteine synthetase, the key enzyme of GSH synthesis, and the results compared with the effects of exogenously added GSH. Although foliar GSH levels were 3-4-fold increased in the transgenic plants, the activities of enzymes of sulphate assimilation, namely ATP sulphurylase, adenosine 5'-phosphosulphate reductase (APR), sulphite reductase, serine acetyltransferase, and O-acetylserine (thiol)lyase were not affected in three transgenic lines compared with the wild type. Also the mRNA levels of these enzymes were not altered by the increased GSH levels. By contrast, an increase in GSH content due to exogenously supplied GSH resulted in a strong reduction in APR activity and mRNA accumulation. This feedback regulation was reverted by simultaneous addition of O-acetylserine (OAS). However, OAS measurements revealed that OAS cannot be the only signal responsible for the lack of feedback regulation of APR by GSH in the transgenic poplars.

Cloning, Molecular↗

PubMed2004

Differences in the influx of glutamine and nitrate into Viscum album from the xylem sap of its hosts.

The flux of inorganic and organic nitrogen into the mistletoe Viscum album L. from the xylem sap of a deciduous (Populus x euamericana) and a coniferous host (Abies alba Mill.) was analyzed. For this purpose, a perfusion system was developed in which the xylem sap of the host was replaced by an artificial perfusion solution. With this system flux rates into the mistletoe were determined in feeding experiments either with the organic nitrogen source [1,2-13C2]glutamine at high and the inorganic nitrogen source 15NO3- at low concentration or vice versa. Glutamine influx was already saturated at the low concentration in the xylem sap and was--different from nitrate--not enhanced, when a 250-fold higher concentration was applied. Nitrate influx matched glutamine influx only at high inorganic/organic nitrogen ratios in the perfusion solution. This result indicates a preferential influx of glutamine over nitrate from the host xylem into the mistletoe at the concentrations found in the xylem sap of trees. Surprisingly, a high percentage of both N sources were accumulated in the mistletoe stem, indicating excessive N nutrition of the mistletoe leaves. Since 13C isotope signature was significantly reduced in the outflowing perfusion solution, either an upload of organic compounds from the phloem into the xylem, or an efflux of organic compounds from haustorium of mistletoe into the xylem has to be assumed. 15N isotope signatures enriched in the outflowing perfusion solution support the idea of a nitrate uptake system at the host xylem-haustorium interface, which favors the light N isotope of nitrate.

Germany↗

PubMed2004

Root uptake, transport, and metabolism of externally applied glutathione in Phaseolus vulgaris seedlings.

The most abundant thiol in beans (Phaseolus vulgaris L. cv. Saxa) is the tripeptide homoglutathione (hGSH) rather than glutathione (GSH). At the whole-plant level the GSH content is less than 0.5% of the hGSH content. In the present study GSH was supplied to the roots of bean seedlings to test whether GSH can be taken up by roots and transported to the shoot. Therefore, 12-day-old plants were exposed to 1 mmol/L GSH for 4, 8 and 24 h prior to harvest. In response to this GSH exposure, elevated GSH contents were found in all tissues. After 4 h the GSH content increased in the roots from 1 +/- 1 to 22 +/- 2 nmol GSH g(-1) fresh weight (FW), in the leaves from 2 +/- 1 to 9 +/- 4 nmol GSH g(-1) FW, and in the apex from 30 +/- 5 to 75 +/- 4 nmol GSH g(-1) FW. These data indicate that GSH is taken up by bean roots and is transported to above above-ground parts of the plants. Roots exposed to GSH for 24 h contained 2-fold higher cysteine (Cys) and hGSH contents than the controls. Apparently, GSH taken up by the roots is not only loaded into the xylem but also partially degraded and used for hGSH synthesis.

Biological Transport, Active↗