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  • 1
    Language: English
    In: Planta, 2015, Vol.241(3), pp.579-589
    Description: Byline: Bin Liu (1), Heinz Rennenberg (1,2), Jurgen Kreuzwieser (1) Keywords: Nitrate; Nitrate reductase; Nitric oxide emission; Oxygen deficiency; Root-to-shoot transport Abstract: Main conclusion Hypoxia leads to NO formation in poplar roots. Additionally, either NO or a NO derivative is transported from the roots to the shoot causing NO emission from aboveground plant organs. Nitric oxide (NO) is involved in the response of plants to various forms of stress including hypoxia. It also seems to play an important role in stomatal closure during stress exposure. In this study, we investigated the formation of NO in roots of intact poplar (Populus x canescens) plants in response to hypoxia, as well as its dependence on nitrate availability. We further addressed the question if root hypoxia triggers NO emission from aboveground plant parts, i.e., stems and leaves of young poplar trees. Our results indicate that NO is formed in poplar roots in response to hypoxia and that this production depends on the availability of nitrate and its conversion product nitrite. As long as nitrate was available in the nutrient solution, NO emission of roots occurred in the range of the nitrate concentrations (10--100 A[micro]M) tested, NO emission was widely independent on nitrate concentration. However, the time period in which NO was emitted and the total amount of NO emitted strongly depended on the nitrate concentration of the solution. Hypoxia also led to increased NO emissions from the leaves and stems of the trees. There was a tight correlation between leaf and stem NO emission of hypoxia-treated plants. We propose that NO is produced by nitrate reductase in the roots and either NO itself, a metabolic NO precursor, or a NO derivative is transported in the xylem sap of the trees from the roots to the shoot thereby mediating NO emission from aboveground parts of the plant. Author Affiliation: (1) Institut fur Forstwissenschaften, Albert-Ludwigs-Universitat Freiburg, Georges-Kohler-Allee Geb. 053/054, 79110, Freiburg, Germany (2) King Saud University, Riyadh, Saudi Arabia Article History: Registration Date: 31/10/2014 Received Date: 23/07/2014 Accepted Date: 28/10/2014 Online Date: 15/11/2014
    Keywords: Nitrate ; Nitrate reductase ; Nitric oxide emission ; Oxygen deficiency ; Root-to-shoot transport
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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  • 2
    Language: English
    In: Planta, 2016, Vol.243(2), pp.355-368
    Description: To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s00425-015-2411-4 Byline: Rut Sanchez-Bragado (1), Jose Luis Araus (1), Ursula Scheerer (2), Jill E. Cairns (3), Heinz Rennenberg (2), Juan Pedro Ferrio (2,4) Keywords: Corn; Drought tolerance; Grain; Leaf; Organic matter; Stable isotopes; Stem water; Translocational Abstract: Main conclusion This paper provides new insights into source-sink relationships and transpiration processes which will eventually help to interpret [delta] .sup.18 O as a genotype selection and ecophysiological tool for maize adaptation to drought. Oxygen isotope composition ([delt[a].sup.18]O) has been proposed as a phenotyping tool to integrate leaf transpiration in C.sub.4 crops, such as maize. Within this context we hypothesize that [delt[a].sup.18]O in leaves may reflect primarily environmental and genetic variability in evaporative processes, but that this signal may become dampened in transit from source to sink tissues. The aim of this study was to assess the relative importance of transpirative or translocation-related factors affecting [delt[a].sup.18]O in plant tissues of maize. We performed two water regime experiments, one with two varieties under semi-controlled conditions, and another in the field with 100 genotypes during two consecutive years. The [delt[a].sup.18]O in organic matter at the leaf base was strongly correlated with the [delt[a].sup.18]O in stem water, indicating that it could be a good proxy for source water in extensive samplings. Compared to leaves, we observed an 18.sup.O depletion in silks and grains, but not in stem-soluble organic matter. We interpret this as evidence of exchange with unenriched water from source to sink, but mainly occurring within sink tissues. Although grain yield (GY) and physiological variables did not show clear intra-trial patterns against [delt[a].sup.18]O, the only tissues that correlated with GY in the linear regression approach were that of silks, giving an insight of evapotranspirative demand during female flowering and thus of potential maize lines that are better adapted to drought. This finding will eventually help to interpret [delt[a].sup.18]O as a genotype selection and ecophysiological tool for the adaption of maize and other crops to drought, offering insight into source-sink relationships and transpiration processes. Author Affiliation: (1) Unitat de Fisiologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain (2) Chair of Tree Physiology, Institute of Forest Sciences, University of Freiburg, Freiburg im Breisgau, Germany (3) International Maize and Wheat Improvement Center (CIMMYT), Harare, Zimbabwe (4) Department of Crop and Forest Sciences-AGROTECNIO Center, Universitat de Lleida, Avda. Rovira Roure 191, 25198, Lleida, Spain Article History: Registration Date: 19/09/2015 Received Date: 06/08/2015 Accepted Date: 18/09/2015 Online Date: 30/09/2015 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00425-015-2411-4) contains supplementary material, which is available to authorized users.
    Keywords: Corn ; Drought tolerance ; Grain ; Leaf ; Organic matter ; Stable isotopes ; Stem water ; Translocational
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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  • 3
    Language: English
    In: Planta, 2013, Vol.238(1), pp.217-227
    Description: Increasing H 2 O 2 levels in guard cells in response to environmental stimuli are recently considered a general messenger involved in the signaling cascade for the induction of stomatal closure. But little is known as to whether subsidiary cells participate in the H 2 O 2 -mediated stomatal closure of grass plants. In the present study, 2-week-old seedlings of maize ( Zea mays ) were exposed to different degrees of soil water deficit for 3 weeks. The effects of soil water contents on leaf ABA and H 2 O 2 levels and stomatal aperture were investigated using physiological, biochemical, and histochemical approaches. The results showed that even under well-watered conditions, significant amounts of H 2 O 2 were observed in guard cells, whereas H 2 O 2 concentrations in the subsidiary cells were negligible. Decreasing soil water contents led to a significant increase in leaf ABA levels associated with significantly enhanced O 2 − and H 2 O 2 contents, consistent with reduced degrees of stomatal conductance and aperture. The significant increase in H 2 O 2 appeared in both guard cells and subsidiary cells of the stomatal complex, and H 2 O 2 levels increased with decreasing soil water contents. Drought-induced increase in the activity of antioxidative enzymes could not counteract the significant increase in H 2 O 2 levels in guard cells and subsidiary cells. These results indicate that subsidiary cells participate in H 2 O 2 -mediated stomatal closure, and drought-induced H 2 O 2 accumulation in subsidiary cells is involved in the signaling cascade regulating stomatal aperture of grass plants such as maize.
    Keywords: Drought ; Signaling ; HO ; Stomata ; Subsidiary cells ; Maize ( L.)
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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  • 4
    Language: English
    In: Planta, 2019, Vol.249(2), pp.481-495
    Description: Byline: Leila Arab (1), Stefan Seegmueller (2), Jurgen Kreuzwieser (1), Monika Eiblmeier (1), Heinz Rennenberg (1) Keywords: Amino acid; Carbon dioxide; Cellulose; Carbohydrate; Glutathione reductase; Lignin Abstract: Main conclusion Atmospheric p CO .sub.2 impacts Quercus petraea biomass production and cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhances foliar non-structural carbohydrate levels and sucrose contents in a pCO .sub.2 concentration-dependent manner. Sessile oak (Quercus petraea Liebl.) was grown for ca. half a year from seeds at ambient control (525 ppm), 750, 900, and 1000 ppm atmospheric pCO.sub.2 under controlled conditions. Increasing pCO.sub.2 enhanced biomass production, modified the cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhanced the foliar non-structural carbohydrate level, in particular the sucrose content as well as total N content of leaves by increased levels of all major N fractions, i.e., soluble proteins, total amino acids, and structural N. The enhanced total amino acid level was largely due to 2-ketoglutarate and oxalo acetate-derived compounds. Increasing pCO.sub.2 alleviated oxidative stress in the leaves as indicated by reduced [H.sub.2]O.sub.2 contents. High in vitro glutathione reductase activity at reduced [H.sub.2]O.sub.2 contents suggests enhanced ROS scavenging, but increased lipid peroxidation may also have contributed, as indicated by a negative correlation between malone dialdehyde and [H.sub.2]O.sub.2 contents. Almost all these effects were at least partially reversed, when pCO.sub.2 exceeded 750 or 900 ppm. Apparently, the interaction of atmospheric pCO.sub.2 with leaf structural and physiological traits of Q. petraea seedlings is characterized by a dynamic response depending on the pCO.sub.2 level. Author Affiliation: (1) grid.5963.9, Chair of Tree Physiology, Institute of Forest Sciences, University of Freiburg, Georges-Kohler-Allee 53/54, 79110, Freiburg, Germany (2) Forschungsanstalt fur Waldokologie und Forstwirtschaft, Hauptstra[sz]e 16, 67705, Trippstadt, Germany Article History: Registration Date: 21/09/2018 Received Date: 20/08/2018 Accepted Date: 20/09/2018 Online Date: 26/09/2018 Article note: Electronic supplementary material The online version of this article ( https://doi.org/10.1007/s00425-018-3016-5) contains supplementary material, which is available to authorized users.
    Keywords: Amino acid ; Carbon dioxide ; Cellulose ; Carbohydrate ; Glutathione reductase ; Lignin
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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  • 5
    Language: English
    In: Planta, 1982, Vol.154(6), pp.516-524
    Description: H 2 S emission from cucumber ( Cucumis sativus L.) leaf discs supplied with L-cysteine in the dark is inhibited 80–90% by aminooxyacetic acid (AOA), an inhibitor of pyridoxal-phosphate dependent enzymes. Exposure to L-cysteine in the light enhanced the emission of H 2 S in response to this sulfur source. Turning off the light reduced the emission of H 2 S to the rate observed in continuous dark; turning on the light enhanced the emission of H 2 S to the rate observed in continuous light. Therefore, in the light H 2 S emission in response to L-cysteine becomes a partially light-dependent process. Treatment with cyanazine, an inhibitor of photosynthetic electron transport, reduced H 2 S emission in the light to the rate observed in continuous dark, but did not affect H 2 S emission in the dark. In leaf discs pre-exposed to L-cysteine in the light, treatment with cyanazine+ AOA inhibited the emission of H 2 S in response to L-cysteine completely. Therefore, only part of the H 2 S emitted in response to this sulfur source is derived from a light-independent, but pyridoxal-phosphate-dependent process; the balance of the H 2 S emitted is derived from a light-dependent process that can be inhibited by cyanazine. When cucumber leaf discs were supplied with a pulse of L-[ 35S ]cysteine, radioactively labeled H 2 S was emitted in two waves, one during the first hour of exposure to L-cysteine, and a second after 3–4 h; unlabeled H 2 S, however, was emitted continuously. The second wave of emission of labeled H 2 S was not observed in pulse-chase experiments in which sulfate or cyanazine were added to the treatment solution after 3 h of exposure to L-cysteine, or when the lights was turned off. The labeling pattern of sulfur compounds inside cucumber cells supplied with a pulse of L-[ 35 S]cysteine showed that the labeled H 2 S released from L-cysteine partially enters first the sulfite, then the sulfate pool of the cells. The radioactively labeled sulfate, however, is not incorporated into L-cysteine, but enters the H 2 S pool of the cells again. These observations are consistent with the idea of an intracellular sulfur cycle in plant cells. The L-cysteine taken up by the leaf discs seems to be desulfhydrated in a light-independent, but pyridoxal-phosphate-dependent process. The H 2 S synthesized this way may be partially released into the atmosphere; the other part of the H 2 S produced in response to L-cysteine may be oxidized to sulfite, then to sulfate, which is subsequently reduced via the light-depent sulfate assimilation pathway. In the presence of excess L-cysteine, synthesis of additional cysteine may be inhibited, and the sulfide moiety may be split off carrier bound sulfide to enter the H 2 S pool of the cells again. It is suggested that the function of this sulfur cycle may be regulation of the free cysteine pool.
    Keywords: Cucumis ; Cysteine ; Hydrogen sulfide emission ; Sulfur cycle and metabolism
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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  • 6
    Language: English
    In: Planta, 1988, Vol.176(1), pp.68-74
    Description: Photoheterotrophic and heterotrophic suspension cultures of tobacco ( Nicotiana tabacum L.) were grown with 1 mM glutathione (reduced; GSH) as sole source of sulfur. Addition of sulfate to both cultures did not alter the rate of exponential growth, but affected the removal of GSH and sulfate in different ways. In photoheterotrophic suspensions, addition of sulfate caused a decline in the net uptake of GSH, whereas sulfate was taken up by the green cells immediately. In heterotrophic suspensions, however, addition of sulfate did not affect the net uptake of GSH and sulfate was only taken up by the cells after the GSH supply in the medium had been exhausted. Apparently, GSH uptake in photoheterotrophic cells is inhibited by sulfate, whereas sulfate uptake is inhibited by GSH in heterotrophic cells. The differences in the effect of GSH on sulfate uptake in photoheterotrophic and heterotrophic tobacco suspensions cannot be attributed to differences in the kinetic properties of sulfate carriers. In short-time transport experiments, both cultures took up sulfate almost entirely by an active-transport system as shown by experiments with metabolic inhibitors; sulfate transport of both cultures obeyed monophasic Michaelis-Menten kinetics with similar app. K m (photoheterotrophic cells: 16.0±2.0 μM; heterotrophic cells: 11.8±1.8 μM) and V max (photoheterotrophic cells: 323±50 nmol·min -1 ·g -1 dry weight; heterotrophic cells: 233±3 nmol·min -1 ·g -1 dry weight). Temperature- and pH-dependence of sulfate transport showed almost identical patterns. However, the cultures exhibited remarkable differences in the inhibition of sulfur influx by GSH in short-time transport experiments. Whereas 1 mM GSH inhibited sulfate transport into heterotrophic tobacco cells completely, sulfate transport into photoheterotrophic cells proceeded at more than two-thirds of its maximum velocity at this GSH concentration. The mode of action of GSH on sulfate transport in chloroplast-free tobacco cell does not appear to be direct: a 14-h exposure to 1 mM GSH was found to be necessary to completely block sulfate transport; a 4-h time of exposure did not affect this process. Consequently, glutathione does not seem to be a product of sulfur metabolism acting on sulfate-carrier entities by negative feedback control. When transferred to the whole plant, the observed differences in sulfate and glutathione influx into green and chloroplast-free cells may be interpreted as a regulatory device to prevent the uptake of excess sulfate by plants.
    Keywords: Glutathione (transport, regulation) ; Nicotiana ; Solanaceae ; Sultate (transport, regulation) ; Sulfur nutrition
    ISSN: 0032-0935
    E-ISSN: 1432-2048
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