bluuebunny/crossref_metadata_2025_split huggingface dataset:
Xanthophyll Cycle Pigment Localization and Dynamics during Exposure to Low Temperatures and Light Stress inVinca major1
Authors: Verhoeven Amy S. , Adams William W. , Demmig-Adams Barbara , Croce Roberta , Bassi Roberto 
Published: July 2002

AbstractThe distribution of xanthophyll cycle pigments (violaxanthin plus antheraxanthin plus zeaxanthin [VAZ]) among photosynthetic pigment-protein complexes was examined in Vinca majorbefore, during, and subsequent to a photoinhibitory treatment at low temperature. Four pigment-protein complexes were isolated: the core of photosystem (PS) II, the major light-harvesting complex (LHC) protein of PSII (LHCII), the minor light-harvesting proteins (CPs) of PSII (CP29, CP26, and CP24), and PSI with its LHC proteins (PSI-LHCI). In isolated thylakoids 80% of VAZ was bound to protein independently of the de-epoxidation state and was found in all complexes. Plants grown outside in natural sunlight had higher levels of VAZ (expressed per chlorophyll), compared with plants grown in low light in the laboratory, and the additional VAZ was mainly bound to the major LHCII complex, apparently in an acid-labile site. The extent of de-epoxidation of VAZ in high light and the rate of reconversion of Z plus A to V following 2.5 h of recovery were greatest in the free-pigment fraction and varied among the pigment-protein complexes. Photoinhibition caused increases in VAZ, particularly in low-light-acclimated leaves. The data suggest that the photoinhibitory treatment caused an enrichment in VAZ bound to the minor CPs caused by de novo synthesis of the pigments and/or a redistribution of VAZ from the major LHCII complex.
N-Acylethanolamines in Seeds. Quantification of Molecular Species and Their Degradation upon Imbibition1
Authors: Chapman Kent D. , Venables Barney , Markovic Robert , Blair Raymond W. , Bettinger Chris 
Published: July 2002

Abstract
N-Acylethanolamines (NAEs) were quantified in seeds of several plant species and several cultivated varieties of a single species (cotton [Gossypium hirstutum]) by gas chromatography-mass spectroscopy. The total NAE content of dry seeds ranged from 490 ± 89 ng g−1fresh weight in pea (Pisum sativum cv early Alaska) to 1,608 ± 309 ng g−1 fresh weight in cotton (cv Stoneville 7A glandless). Molecular species of NAEs in all seeds contained predominantly 16C and 18C fatty acids, withN-linoleoylethanolamine (NAE18:2) being the most abundant (approaching 1,000 ng g−1 fresh weight in cottonseeds). Total NAE levels dropped drastically following 4 h of imbibition in seeds of pea, cotton, and peanut (Arachis hypogea cv Virginia), and this decline was most pronounced for NAE18:2. A novel enzyme activity was identified in cytosolic fractions of imbibed cottonseeds that hydrolyzed NAE18:2 in vitro. NAE degradation was optimal at 35°C in 50 mm MES buffer, pH 6.5, and was inhibited by phenylmethylsulfonyl fluoride and 5,5′-dithio-bis(2-nitrobenzoic acid), which is typical of other amide hydrolases. Amidohydrolase activity in cytosolic fractions exhibited saturation kinetics toward the NAE18:2 substrate, with an apparent Km of 65 μm and aVmax of 83 nmol min−1mg−1 protein. Total NAE amidohydrolase activity increased during seed imbibition, with the highest levels (about four times that in dry seeds) measured 2 h after commencing hydration. NAEs belong to the family of “endocannabinoids,” which have been identified as potent lipid mediators in other types of eukaryotic cells. This raises the possibility that their imbibition-induced metabolism in plants is involved in the regulation of seed germination.
Differential Ion Accumulation and Ion Fluxes in the Mesophyll and Epidermis of Barley
Authors: Karley Alison J. , Leigh Roger A. , Sanders Dale 
Published: July 2002

Abstract
In barley (Hordeum vulgare L.) leaves, differential ion accumulation commonly results in inorganic phosphate (Pi) being confined to the mesophyll and Ca2+ to the epidermis, with preferential epidermal accumulation of Cl−, Na+, and some other ions. The pattern was confirmed in this study for major inorganic anions and cations by analysis of barley leaf protoplasts. The work focused on the extent to which differences in plasma membrane ion transport processes underlie these observations. Ion transport across the plasma membrane of barley epidermal and mesophyll protoplasts was investigated electrophysiologically (by microelectrode impalement and patch clamping) and radiometrically. Data from both approaches suggested that similar types of ion-selective channels and membrane transporters, which catalyze the transport of Ca2+, K+, Na+, and Pi, exist in the plasma membrane of the two cell types. In general, the simple presence or absence of ion transporters could not explain cell-type-specific differences in ion accumulation. However, patch-clamp data suggested that differential regulation of instantaneously activating ion channels in the plasma membrane could explain the preferential accumulation of Na+ in the epidermis.
Sodium-Dependent Nitrate Transport at the Plasma Membrane of Leaf Cells of the Marine Higher PlantZostera marinaL.
Authors: Garcı́a-Sánchez Marı́a J. , Jaime M. Paz , Ramos Alberto , Sanders Dale , Fernández JoséA. 
Published: July 2002

AbstractNO3 −is present at micromolar concentrations in seawater and must be absorbed by marine plants against a steep electrochemical potential difference across the plasma membrane. We studied NO3 − transport in the marine angiospermZostera marina L. to address the question of how NO3 − uptake is energized. Electrophysiological studies demonstrated that micromolar concentrations of NO3 − induced depolarizations of the plasma membrane of leaf cells. Depolarizations showed saturation kinetics (K m = 2.31 ± 0.78 μm NO3 −) and were enhanced in alkaline conditions. The addition of NO3 − did not affect the membrane potential in the absence of Na+, but depolarizations were restored when Na+ was resupplied. NO3 −-induced depolarizations at increasing Na+ concentrations showed saturation kinetics (K m = 0.72 ± 0.18 mmNa+). Monensin, an ionophore that dissipates the Na+ electrochemical potential, inhibited NO3 −-evoked depolarizations by 85%, and NO3 − uptake (measured by depletion from the external medium) was stimulated by Na+ ions and by light. Our results strongly suggest that NO3 − uptake in Z. marina is mediated by a high-affinity Na+-symport system, which is described here (for the first time to our knowledge) in an angiosperm. Coupling the uptake of NO3 − to that of Na+ enables the steep inwardly-directed electrochemical potential for Na+to drive net accumulation of NO3 − within leaf cells.
Activation Tagging in Arabidopsis
Authors: Weigel Detlef , Ahn Ji Hoon , Blázquez Miguel A. , Borevitz Justin O. , Christensen Sioux K. , Fankhauser Christian , Ferrándiz Cristina , Kardailsky Igor , Malancharuvil Elizabeth J. , Neff Michael M. , Nguyen Jasmine Thuy , Sato Shusei , Wang Zhi-Yong , Xia Yiji , Dixon Richard A. , Harrison Maria J. , Lamb Chris J. , Yanofsky Martin F. , Chory Joanne 
Published: July 2002

Abstract
Activation tagging using T-DNA vectors that contain multimerized transcriptional enhancers from the cauliflower mosaic virus (CaMV) 35S gene has been applied to Arabidopsis plants. New activation-tagging vectors that confer resistance to the antibiotic kanamycin or the herbicide glufosinate have been used to generate several tens of thousands of transformed plants. From these, over 30 dominant mutants with various phenotypes have been isolated. Analysis of a subset of mutants has shown that overexpressed genes are almost always found immediately adjacent to the inserted CaMV 35S enhancers, at distances ranging from 380 bp to 3.6 kb. In at least one case, the CaMV 35S enhancers led primarily to an enhancement of the endogenous expression pattern rather than to constitutive ectopic expression, suggesting that the CaMV 35S enhancers used here act differently than the complete CaMV 35S promoter. This has important implications for the spectrum of genes that will be discovered by this method.
Immunolocalization of a Cysteine Protease in Vacuoles, Vesicles, and Symbiosomes of Pea Nodule Cells
Authors: Vincent Jason L. , Brewin Nicholas J. 
Published: July 2002

Abstract
PsCYP15A is a cysteine protease from pea (Pisum sativum L.). It was first recognized as an up-regulated transcript in wilted shoots and subsequently in root nodules containingRhizobium. Proteolytic activity of PsCYP15A in nodule extracts is now reported following immunopurification with polyclonal antiserum raised against recombinant antigen. Western-blot analysis indicated two forms of PsCYP15A, a pro-form (approximately 38 kD) and a mature form (approximately 30 kD). Both forms were present in most tissue samples, but only the mature form was isolated from cell-fractionated symbiosomes containing nitrogen-fixing bacteroids. Immunolabeling of nodule sections showed localization of PsCYP15A antigen in large vacuolar bodies, cytoplasmic vesicles, and the perisymbiont space. Immunolabeling of tissue sections from wilted shoots also indicated the presence of PsCYP15A in vacuoles and cytoplasmic vesicles. This protease may be involved in the adaptation to changes in cell turgor, both in wilted shoots and in nodule tissue. Additionally, the protease may be involved in protein turnover in the symbiosome compartment.
Purification and Characterization of Bifunctional Lysine-Ketoglutarate Reductase/Saccharopine Dehydrogenase from Developing Soybean Seeds
Authors: Miron Daphna , Ben-Yaacov Sari , Reches Dalit , Schupper Avigail , Galili Gad 
Published: July 2002

Abstract
Both in mammals and plants, excess lysine (Lys) is catabolized via saccharopine into α-amino adipic semialdehyde and glutamate by two consecutive enzymes, Lys-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH), which are linked on a single bifunctional polypeptide. To study the control of metabolite flux via this bifunctional enzyme, we have purified it from developing soybean (Glycine max) seeds. LKR activity of the bifunctional LKR/SDH possessed relatively high K m for its substrates, Lys and α-ketoglutarate, suggesting that this activity may serve as a rate-limiting step in Lys catabolism. Despite their linkage, the LKR and SDH enzymes possessed significantly different pH optima, suggesting that SDH activity of the bifunctional enzyme may also be rate-limiting in vivo. We have previously shown that Arabidopsis plants contain both a bifunctional LKR/SDH and a monofunctional SDH enzymes (G. Tang, D. Miron, J.X. Zhu-Shimoni, G. Galili [1997] Plant Cell 9: 1–13). In the present study, we found no evidence for the presence of such a monofunctional SDH enzyme in soybean seeds. These results may provide a plausible regulatory explanation as to why various plant species accumulate different catabolic products of Lys.
Differential Interaction of Maize Root Ferredoxin:NADP+ Oxidoreductase with Photosynthetic and Non-Photosynthetic Ferredoxin Isoproteins
Authors: Onda Yayoi , Matsumura Tomohiro , Kimata-Ariga Yoko , Sakakibara Hitoshi , Sugiyama Tatsuo , Hase Toshiharu 
Published: July 2002

AbstractIn higher plants ferredoxin (Fd):NADP+ oxidoreductase (FNR) and Fd are each distributed in photosynthetic and non-photosynthetic organs as distinct isoproteins. We have cloned cDNAs for leaf FNR (L-FNR I and L-FNR II) and root FNR (R-FNR) from maize (Zea mays L.), and produced recombinant L-FNR I and R-FNR to study their enzymatic functions through kinetic and Fd-binding analyses. The K m value obtained by assay for a diaphorase activity indicated that R-FNR had a 10-fold higher affinity for NADPH than L-FNR I. When we assayed for NADPH-cytochromec reductase activity using maize photosynthetic Fd (Fd I) and non-photosynthetic Fd (Fd III), the R-FNR showed a marked difference in affinity between these two Fd isoproteins; theK m for Fd III was 3.0 μm and that for Fd I was 29 μm. Consistent with this, the dissociation constant for the R-FNR:Fd III complex was 10-fold smaller than that of the R-FNR:Fd I complex. This differential binding capacity was confirmed by an affinity chromatography of R-FNR on Fd-sepharose with stronger binding to Fd III. L-FNR I showed no such differential interaction with Fd I and Fd III. These data demonstrated that R-FNR has the ability to discriminate between these two types of Fds. We propose that the stronger interaction of R-FNR with Fd III is crucial for an efficient electron flux of NADPH-FNR-Fd cascade, thus supporting Fd-dependent metabolism in non-photosynthetic organs.
Exploiting Secondary Growth in Arabidopsis. Construction of Xylem and Bark cDNA Libraries and Cloning of Three Xylem Endopeptidases
Authors: Zhao Chengsong , Johnson Bobby J. , Kositsup Boonthida , Beers Eric P. 
Published: July 2002

Abstract
The root-hypocotyl of Arabidopsis produces a relatively large amount of secondary vascular tissue when senescence is delayed by the removal of inflorescences, and plants are grown at low population density. Peptidase zymograms prepared from isolated xylem and phloem revealed the existence of distinct proteolytic enzyme profiles within these tissues. cDNA libraries were constructed from isolated xylem and bark of the root-hypocotyl and screened for cDNAs coding for cysteine, serine, and aspartic peptidases. Three cDNAs, two putative papain-type cysteine peptidases (XCP1 and XCP2) and one putative subtilisin-type serine peptidase (XSP1), were identified from the xylem library for further analysis. Using RNA gel blots it was determined that these peptidases were expressed in the xylem and not in the bark. Quantitative reverse transcriptase-polymerase chain reaction confirmed the RNA gel-blot results and revealed high levels of XCP1 and XCP2 mRNA in stems and flowers of the infloresence. A poly-histidine-tagged version of XCP1 was purified from Escherichia coli by denaturing metal-chelate chromatography. Following renaturation, the 40-kD recombinant XCP1 was not proteolytically active. Activation was achieved by incubation of recombinant XCP1 at pH 5.5 and was dependent on proteolytic processing of the 40-kD inactive polypeptide to a 26-kD active peptidase.
Regulation of Sulfur Nutrition in Wild-Type and Transgenic Poplar Over-Expressing γ-Glutamylcysteine Synthetase in the Cytosol as Affected by Atmospheric H2S
Authors: Herschbach Cornelia , van der Zalm Esther , Schneider Andrea , Jouanin Lise , De Kok Luit J. , Rennenberg Heinz 
Published: July 2002

Abstract
This study with poplar (Populus tremula ×Populus alba) cuttings was aimed to test the hypothesis that sulfate uptake is regulated by demand-driven control and that this regulation is mediated by phloem-transported glutathione as a shoot-to-root signal. Therefore, sulfur nutrition was investigated at (a) enhanced sulfate demand in transgenic poplar over-expressing γ-glutamylcysteine (γ-EC) synthetase in the cytosol and (b) reduced sulfate demand during short-term exposure to H2S. H2S taken up by the leaves increased cysteine, γ-EC, and glutathione concentrations in leaves, xylem sap, phloem exudate, and roots, both in wild-type and transgenic poplar. The observed reduced xylem loading of sulfate after H2S exposure of wild-type poplar could well be explained by a higher glutathione concentration in the phloem. In transgenic poplar increased concentrations of glutathione and γ-EC were found not only in leaves, xylem sap, and roots but also in phloem exudate irrespective of H2S exposure. Despite enhanced phloem allocation of glutathione and its accumulation in the roots, sulfate uptake was strongly enhanced. This finding is contradictory to the hypothesis that glutathione allocated in the phloem reduces sulfate uptake and its transport to the shoot. Correlation analysis provided circumstantial evidence that the sulfate to glutathione ratio in the phloem may control sulfate uptake and loading into the xylem, both when the sulfate demand of the shoot is increased and when it is reduced.
Redox Control of ntcA Gene Expression in Synechocystis sp. PCC 6803. Nitrogen Availability and Electron Transport Regulate the Levels of the NtcA Protein
Authors: Alfonso Miguel , Perewoska Irène , Kirilovsky Diana 
Published: July 2002

Abstract
In this work we have studied the influence of the cellular redox status in the expression of the Synechocystis sp. PCC 6803 ntcA gene. Two different ntcAtranscripts with different 5′ ends were detected, depending on the different dark/light or nitrogen availability conditions. Accumulation of a 0.8-kb ntcA message was light and nitrogen dependent, whereas a longer 1.2-kb ntcA transcript was neither light nor nitrogen regulated. NtcA protein levels increased concomitantly with the accumulation of the 0.8-kb ntcAtranscript. The light-dependent accumulation of the ntcAgene and the NtcA protein was sensitive to electron transport inhibitors. In addition, Glc-grown Synechocystis sp. cells showed a similar ntcA expression pattern in darkness to that observed under illumination. These data suggested that electron transport, and not light per se may regulatentcA gene expression. Primer extension analysis, together with gel mobility-shift assays, demonstrated that in vitro, the Synechocystis sp. NtcA protein specifically bound to the putative promoter region from the light/nitrogen-dependentntcA transcript but not to that from the constitutive 1.2-kb ntcA mRNA. Band-shift experiments carried out in the presence of thiol oxidizing/modifiying agents and different reducing/oxidizing conditions suggested that NtcA binding to its own promoter was under a thiol-dependent redox mechanism. Our results suggest that the cellular redox status plays a central role in the autoregulatory mechanism of the NtcA protein.
Guard Cell Volume and Pressure Measured Concurrently by Confocal Microscopy and the Cell Pressure Probe,
Authors: Franks Peter J. , Buckley Thomas N. , Shope Joseph C. , Mott Keith A. 
Published: July 2002

Abstract
Guard cell turgor pressures in epidermal peels of broad bean (Vicia faba) were measured and controlled with a pressure probe. At the same time, images of the guard cell were acquired using confocal microscopy. To obtain a clear image of guard cell volume, a fluorescent dye that labels the plasma membrane was added to the solution bathing the epidermal peel. At each pressure, 17 to 20 optical sections (each 2 μm thick) were acquired. Out-of-focus light in these images was removed using blind deconvolution, and volume was estimated using direct linear integration. As pressure was increased from as low as 0.3 MPa to as high as 5.0 MPa, guard cell volume increased in a saturating fashion. The elastic modulus was calculated from these data and was found to range from approximately 2 to 40 MPa. The data allow inference of guard cell osmotic content from stomatal aperture and facilitate accurate mechanistic modeling of epidermal water relations and stomatal functioning.
Active Oxygen Produced during Selective Excitation of Photosystem I Is Damaging Not Only to Photosystem I, But Also to Photosystem II
Authors: Tjus Staffan Erling , Scheller Henrik Vibe , Andersson Bertil , Møller Birger Lindberg 
Published: July 2002

Abstract
With the aim to specifically study the molecular mechanisms behind photoinhibition of photosystem I, stacked spinach (Spinacia oleracea) thylakoids were irradiated at 4°C with far-red light (&gt;715 nm) exciting photosystem I, but not photosystem II. Selective excitation of photosystem I by far-red light for 130 min resulted in a 40% inactivation of photosystem I. It is surprising that this treatment also caused up to 90% damage to photosystem II. This suggests that active oxygen produced at the reducing side of photosystem I is highly damaging to photosystem II. Only a small pool of the D1-protein was degraded. However, most of the D1-protein was modified to a slightly higher molecular mass, indicative of a damage-induced conformational change. The far-red illumination was also performed using destacked and randomized thylakoids in which the distance between the photosystems is shorter. Upon 130 min of illumination, photosystem I showed an approximate 40% inactivation as in stacked thylakoids. In contrast, photosystem II only showed 40% inactivation in destacked and randomized thylakoids, less than one-half of the inactivation observed using stacked thylakoids. In accordance with this, photosystem II, but not photosystem I is more protected from photoinhibition in destacked thylakoids. Addition of active oxygen scavengers during the far-red photosystem I illumination demonstrated superoxide to be a major cause of damage to photosystem I, whereas photosystem II was damaged mainly by superoxide and hydrogen peroxide.
Nitrogen Starvation-Induced Chlorosis inSynechococcus PCC 7942. Low-Level Photosynthesis As a Mechanism of Long-Term Survival
Authors: Sauer Jörg , Schreiber Ulrich , Schmid Roland , Völker Uwe , Forchhammer Karl 
Published: July 2002

Abstract
Cells of the non-diazotrophic cyanobacteriumSynechococcus sp. strain PCC 7942 acclimate to nitrogen deprivation by differentiating into non-pigmented resting cells, which are able to survive prolonged periods of starvation. In this study, the physiological properties of the long-term nitrogen-starved cells are investigated in an attempt to elucidate the mechanisms of maintenance of viability. Preservation of energetic homeostasis is based on a low level of residual photosynthesis; activities of photosystem II and photosystem I were approximately 0.1% of activities of vegetatively growing cells. The low levels of photosystem I activity were measured by a novel colorimetric assay developed from the activity staining of ferredoxin:NADP+ oxidoreductase. Photosystem II reaction centers, as determined by chlorophyll fluorescence measurements, exhibited normal properties, although the efficiency of light harvesting was significantly reduced compared with that of control cells. Long-term chlorotic cells carried out protein synthesis at a very low, but detectable level, as revealed by in vivo [35S]methionine labeling and two-dimensional gel electrophoresis. In conjunction with the very low levels of total cellular protein contents, this implies a continuous protein turnover during chlorosis. Synthesis of components of the photosynthetic apparatus could be detected, whereas factors of the translational machinery were stringently down-regulated. Beyond the massive loss of protein during acclimation to nitrogen deprivation, two proteins that were identified as SomA and SomB accumulated due to an induced expression following nitrogen reduction.
An Insight into Cell Elasticity and Load-Bearing Ability. Measurement and Theory
Authors: Wei Chunfang , Lintilhac Philip M. , Tanguay Jason J. 
Published: July 2002

Abstract
We have studied the elasticity and load bearing ability of plant tissue at the cellular level, using onion (Allium cepa) epidermal cells. The Young's modulus and Poisson's ratio of the cells were obtained by loading a tensile force on onion epidermal peels of different turgor pressures, and measuring the elongation and the lateral contraction of the peels. The Young's moduli and the Poisson's ratios ranged from 3.5 to 8.0 MPa and 0.18 to 0.30, respectively. To determine the effects of cell elasticity and turgor pressure on the cell's ability to bear load, we loaded a small glass ball onto a cell and measured the projected contact area between the ball and the cell. Unlike previous studies, we considered the cell as a whole entity, and utilized the Boussinesq's solution to derive the relevant equations that related the elastic parameters and cell deformation. For cells with a turgor pressure ≥ 0.34 MPa, the predicted contact area agreed well with the measured area. The equations could also predict cell turgor pressure with a deviation from the measured value of 0.01 MPa. This study gives strong support to ball tonometry, a new method of measuring cell turgor pressure.