bluuebunny/crossref_metadata_2025_split huggingface dataset:
Altered Growth of Transgenic Tobacco Lacking Leaf Cytosolic Pyruvate Kinase1
Authors: Knowles Vicki L. , McHugh Sylvia G. , Hu Zhiyuan , Dennis David T. , Miki Brian L. , Plaxton William C. 
Published: July 2002

Abstract
Previously, we reported that transformation of tobacco (Nicotiana tabacum L.) with a vector containing a potato cytosolic pyruvate kinase (PKc) cDNA generated two plant lines specifically lacking leaf PKc (PKc−) as a result of co-suppression. PKc deficiency in these primary transformants did not appear to alter plant development, although root growth was not examined. Here we report a striking reduction in root growth of homozygous progeny of both PKc− lines throughout development under moderate (600 μE m−2 s−1) or low (100 μE m−2 s−1) light intensities. When both PKc− lines were cultivated under low light, shoot and flower development were also delayed and leaf indentations were apparent. Leaf PK activity in the transformants was significantly decreased at all time points examined, whereas root activities were unaffected. Polypeptides corresponding to PKc were undetectable on immunoblots of PKc− leaf extracts, except in 6-week-old low-light-grown PKc− plants, in which leaf PKc expression appeared to be greatly reduced. The metabolic implications of the kinetic characteristics of partially purified PKc from wild-type tobacco leaves are discussed. Overall, the results suggest that leaf PKc deficiency leads to a perturbation in source-sink relationships.
Fruit Development in Trillium1
Authors: Lapointe Line 
Published: July 2002

AbstractLeaves are the main source of carbon for fruit maturation in most species. However, in plants seeing contrasting light conditions such as some spring plants, carbon fixed during the spring could be used to support fruit development in the summer, when photosynthetic rates are low. We monitored carbohydrate content in the rhizome (a perennating organ) and the aboveground stem of trillium (Trillium erectum) over the entire growing season (May–November). At the beginning of the fruiting stage, stems carrying a developing fruit were harvested, their leaves were removed, and the leafless stems were maintained in aqueous solution under controlled conditions up to full fruit maturation. These experiments showed that stem carbohydrate content was sufficient to support fruit development in the absence of leaves and rhizome. This is the first reported case, to our knowledge, of complete fruit development sustained only by a temporary carbohydrate reservoir. This carbohydrate accumulation in the stem during the spring enables the plant to make better use of the high irradiances occurring at that time. Many other species might establish short-term carbohydrate reservoirs in response to seasonal changes in growing conditions.
Aluminum Resistance in the Arabidopsis Mutantalr-104 Is Caused by an Aluminum-Induced Increase in Rhizosphere pH1
Authors: Degenhardt Jörg , Larsen Paul B. , Howell Stephen H. , Kochian Leon V. 
Published: July 2002

AbstractA mechanism that confers increased Al resistance in the Arabidopsis thaliana mutantalr-104 was investigated. A modified vibrating microelectrode system was used to measure H+ fluxes generated along the surface of small Arabidopsis roots. In the absence of Al, no differences in root H+ fluxes between wild type and alr-104 were detected. However, Al exposure induced a 2-fold increase in net H+ influx inalr-104 localized to the root tip. The increased flux raised the root surface pH of alr-104 by 0.15 unit. A root growth assay was used to assess the Al resistance ofalr-104 and wild type in a strongly pH-buffered nutrient solution. Increasing the nutrient solution pH from 4.4 to 4.5 significantly increased Al resistance in wild type, which is consistent with the idea that the increased net H+ influx can account for greater Al resistance in alr-104. Differences in Al resistance between wild type and alr-104 disappeared when roots were grown in pH-buffered medium, suggesting that Al resistance in alr-104 is mediated only by pH changes in the rhizosphere. This mutant provides the first evidence, to our knowledge, for an Al-resistance mechanism based on an Al-induced increase in root surface pH.
Three Mechanisms for the Calcium Alleviation of Mineral Toxicities
Authors: Kinraide Thomas B. 
Published: July 2002

Abstract
Ca2+ in rooting medium is essential for root elongation, even in the absence of added toxicants. In the presence of rhizotoxic levels of Al3+, H+, or Na+ (or other cationic toxicants), supplementation of the medium with higher levels of Ca2+alleviates growth inhibition. Experiments to determine the mechanisms of alleviation entailed measurements of root elongation in wheat (Triticum aestivum L. cv Scout 66) seedlings in controlled medium. A Gouy-Chapman-Stern model was used to compute the electrical potentials and the activities of ions at the root-cell plasma membrane surfaces. Analysis of root elongation relative to the computed surface activities of ions revealed three separate mechanisms of Ca2+ alleviation. Mechanism I is the displacement of cell-surface toxicant by the Ca2+-induced reduction in cell-surface negativity. Mechanism II is the restoration of Ca2+ at the cell surface if the surface Ca2+has been reduced by the toxicant to growth-limiting levels. Mechanism III is the collective ameliorative effect of Ca2+ beyond mechanisms I and II, and may involve Ca2+-toxicant interactions at the cell surface other than the displacement interactions of mechanisms I and II. Mechanism I operated in the alleviation of all of the tested toxicities; mechanism II was generally a minor component of alleviation; and mechanism III was toxicant specific and operated strongly in the alleviation of Na+toxicity, moderately in the alleviation of H+ toxicity, and not at all in the alleviation of Al3+ toxicity.
Mitochondrial Contribution to the Anoxic Ca2+ Signal in Maize Suspension-Cultured Cells
Authors: Subbaiah Chalivendra C. , Bush Douglas S. , Sachs Martin M. 
Published: July 2002

Abstract
Anoxia induces a rapid elevation of the cytosolic Ca2+concentration ([Ca2+]cyt) in maize (Zea mays L.) cells, which is caused by the release of the ion from intracellular stores. This anoxic Ca2+ release is important for gene activation and survival in O2-deprived maize seedlings and cells. In this study we examined the contribution of mitochondrial Ca2+ to the anoxic [Ca2+]cyt elevation in maize cells. Imaging of intramitochondrial Ca2+ levels showed that a majority of mitochondria released their Ca2+ in response to anoxia and took up Ca2+ upon reoxygenation. We also investigated whether the mitochondrial Ca2+ release contributed to the increase in [Ca2+]cyt under anoxia. Analysis of the spatial association between anoxic [Ca2+]cytchanges and the distribution of mitochondrial and other intracellular Ca2+ stores revealed that the largest [Ca2+]cyt increases occurred close to mitochondria and away from the tonoplast. In addition, carbonylcyanide p-trifluoromethoxyphenyl hydrazone treatment depolarized mitochondria and caused a mild elevation of [Ca2+]cyt under aerobic conditions but prevented a [Ca2+]cyt increase in response to a subsequent anoxic pulse. These results suggest that mitochondria play an important role in the anoxic elevation of [Ca2+]cyt and participate in the signaling of O2 deprivation.
Changes in Cell Wall Composition during Ripening of Grape Berries
Authors: Nunan Kylie J. , Sims Ian M. , Bacic Antony , Robinson Simon P. , Fincher Geoffrey B. 
Published: July 2002

AbstractCell walls were isolated from the mesocarp of grape (Vitis vinifera L.) berries at developmental stages from before veraison through to the final ripe berry. Fluorescence and light microscopy of intact berries revealed no measurable change in cell wall thickness as the mesocarp cells expanded in the ripening fruit. Isolated walls were analyzed for their protein contents and amino acid compositions, and for changes in the composition and solubility of constituent polysaccharides during development. Increases in protein content after veraison were accompanied by an approximate 3-fold increase in hydroxyproline content. The type I arabinogalactan content of the pectic polysaccharides decreased from approximately 20 mol % of total wall polysaccharides to about 4 mol % of wall polysaccharides during berry development. Galacturonan content increased from 26 to 41 mol % of wall polysaccharides, and the galacturonan appeared to become more soluble as ripening progressed. After an initial decrease in the degree of esterification of pectic polysaccharides, no further changes were observed nor were there large variations in cellulose (30–35 mol % of wall polysaccharides) or xyloglucan (approximately 10 mol % of wall polysaccharides) contents. Overall, the results indicate that no major changes in cell wall polysaccharide composition occurred during softening of ripening grape berries, but that significant modification of specific polysaccharide components were observed, together with large changes in protein composition.
Arginase Is Inoperative in Developing Soybean Embryos1
Authors: Goldraij Ariel , Polacco Joe C. 
Published: July 2002

Abstract
Arginase (EC 3.5.3.1) transcript level and activity were measured in soybean (Glycine maxL.) embryos from the reserve deposition stage to postgermination. Using a cDNA probe for a small soybean arginase gene family, no transcript was detected in developing embryos. However, arginase transcripts increased sharply on germination, reaching a maximum at 3 to 5 d after germination. There was low but measurable in vitro arginase specific activity in developing embryos (less than 6% of seedling maximum). During germination arginase specific activity increased in parallel with the sharply increasing arginase transcript level. Seedling arginase activity was largely localized in cotyledons. Arginase activity was assayed in vivo by measuring urea accumulation in a urease-deficient mutant. No urea was detected in developing embryos, whereas accumulated urea paralleled arginase specific activity and transcript level in germinating seedlings. As in planta embryos, cultured cotyledons did not accumulate urea when arginine (Arg) was provided with other amino acids in a “mock” seed-coat exudate. Arg as the sole nitrogen source was converted to urea but did not support cotyledon growth. There appeared to be a lack of recruitment of the low-level arginase activity to hydrolyze free Arg in developing embryos, thus avoiding a futile urea cycle.
Thermotolerance of Leaf Discs from Four Isoprene-Emitting Species Is Not Enhanced by Exposure to Exogenous Isoprene1
Authors: Logan Barry A. , Monson Russell K. 
Published: July 2002

Abstract
The effects of exogenously supplied isoprene on chlorophyll fluorescence characteristics were examined in leaf discs of four isoprene-emitting plant species, kudzu (Pueraria lobata[Willd.] Ohwi.), velvet bean (Mucunasp.), quaking aspen (Populus tremuloidesMichx.), and pussy willow (Salix discolor Muhl). Isoprene, supplied to the leaves at either 18 μL L−1 in compressed air or 21 μL L−1 in N2, had no effect on the temperature at which minimal fluorescence exhibited an upward inflection during controlled increases in leaf-disc temperature. During exposure to 1008 μmol photons m−2s−1 in an N2 atmosphere, 21 μL L−1 isoprene had no effect on the thermally induced inflection of steady-state fluorescence. The maximum quantum efficiency of photosystem II photochemistry decreased sharply as leaf-disc temperature was increased; however, this decrease was unaffected by exposure of leaf discs to 21 μL L−1 isoprene. Therefore, there were no discernible effects of isoprene on the occurrence of symptoms of high-temperature damage to thylakoid membranes. Our data do not support the hypothesis that isoprene enhances leaf thermotolerance.
The SLENDER Gene of Pea Encodes a Gibberellin 2-Oxidase
Authors: Martin David N. , Proebsting William M. , Hedden Peter 
Published: July 2002

Abstract
The amount of active gibberellin (GA) in plant tissues is determined in part by its rate of catabolism through oxidation at C-2. In pea (Pisum sativumL.) seeds, GA 2-oxidation is controlled by the SLN(SLENDER) gene, a mutation of which produces seedlings characterized by a slender or hyper-elongated phenotype. We cloned a GA 2-oxidase cDNA from immature pea seeds by screening an expression library for enzyme activity. The clone contained a full-length open reading frame encoding a protein of 327 amino acids. Lysate of bacterial cultures expressing the protein converted the C19-GAs, GA1, GA4, GA9, and GA20 to the corresponding 2β-hydroxy products. GA9 and GA20 were also converted to GA51 and GA29 catabolites, respectively. The gene appeared to be one member of a small family of GA 2-oxidases in pea. Transcript was found predominantly in roots, flowers, young fruits, and testae of seeds. The corresponding transcript fromsln pea contained a point mutation and did not produce active enzyme when expressed heterologously. RFLP analysis of a seedling population segregating for SLN andsln alleles showed the homozygous mutant allele co-segregating with the characteristic slender phenotype. We conclude that SLN encodes GA 2-oxidase.
Characterization and Expression of Four Proline-Rich Cell Wall Protein Genes in Arabidopsis Encoding Two Distinct Subsets of Multiple Domain Proteins
Authors: Fowler Thomas J. , Bernhardt Christine , Tierney Mary L. 
Published: July 2002

Abstract
We have characterized the molecular organization and expression of four proline-rich protein genes from Arabidopsis (AtPRPs). These genes predict two classes of cell wall proteins based on DNA sequence identity, repetitive motifs, and domain organization. AtPRP1 and AtPRP3encode proteins containing an N-terminal PRP-like domain followed by a C-terminal domain that is biased toward P, T, Y, and K.AtPRP2 and AtPRP4 represent a second, novel group of PRP genes that encode two-domain proteins containing a non-repetitive N-terminal domain followed by a PRP-like region rich in P, V, K, and C. Northern hybridization analysis indicated that AtPRP1 and AtPRP3 are exclusively expressed in roots, while transcripts encoding AtPRP2 and AtPRP4 were most abundant in aerial organs of the plant. Histochemical analyses of promoter/β-glucuronidase fusions localized AtPRP3 expression to regions of the root containing root hairs. AtPRP2 and AtPRP4expression was detected in expanding leaves, stems, flowers, and siliques. In addition, AtPRP4 expression was detected in stipules and during the early stages of lateral root formation. These studies support a model for involvement of PRPs in specifying cell-type-specific wall structures, and provide the basis for a genetic approach to dissect the function of PRPs during growth and development.
The Role of Chloroplast Electron Transport and Metabolites in Modulating Rubisco Activity in Tobacco. Insights from Transgenic Plants with Reduced Amounts of Cytochrome b/fComplex or Glyceraldehyde 3-Phosphate Dehydrogenase
Authors: Ruuska Sari A. , Andrews T. John , Badger Murray R. , Price G. Dean , von Caemmerer Susanne 
Published: July 2002

Abstract
Leaf metabolites, adenylates, and Rubisco activation were studied in two transgenic tobacco (Nicotiana tabacum L. cv W38) types. Plants with reduced amounts of cytochrome b/f complex (anti-b/f) have impaired electron transport and a low transthylakoid pH gradient that restrict ATP and NADPH synthesis. Plants with reduced glyceraldehyde 3-phosphate dehydrogenase (anti-GAPDH) have a decreased capacity to use ATP and NADPH in carbon assimilation. The activation of the chloroplast NADP-malate dehydrogenase decreased in anti-b/f plants, indicating a low NADPH/NADP+ ratio. The whole-leaf ATP/ADP in anti-b/f plants was similar to wild type, while it increased in anti-GAPDH plants. In both plant types, the CO2 assimilation rates decreased with decreasing ribulose 1,5-bisphosphate concentrations. In anti-b/f plants, CO2 assimilation was further compromised by reduced carbamylation of Rubisco, whereas in anti-GAPDH plants the carbamylation remained high even at subsaturating ribulose 1,5-bisphosphate concentrations. We propose that the low carbamylation in anti-b/f plants is due to reduced activity of Rubisco activase. The results suggest that light modulation of activase is not directly mediated via the electron transport rate or stromal ATP/ADP, but some other manifestation of the balance between electron transport and the consumption of its products. Possibilities include the transthylakoid pH gradient and the reduction state of the acceptor side of photosystem I and/or the degree of reduction of the thioredoxin pathway.
Removal of Feedback Inhibition of Δ1-Pyrroline-5-Carboxylate Synthetase Results in Increased Proline Accumulation and Protection of Plants from Osmotic Stress
Authors: Hong Zonglie , Lakkineni Karuna , Zhang Zhongming , Verma Desh Pal S. 
Published: July 2002

AbstractThe Δ1-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned) is the rate-limiting enzyme in proline (Pro) biosynthesis in plants and is subject to feedback inhibition by Pro. It has been suggested that the feedback regulation of P5CS is lost in plants under stress conditions. We compared Pro levels in transgenic tobacco (Nicotiana tabacum) plants expressing a wild-type form of Vigna aconitifolia P5CS and a mutated form of the enzyme (P5CSF129A) whose feedback inhibition by Pro was removed by site-directed mutagenesis. Transgenic plants expressing P5CSF129A accumulated about 2-fold more Pro than the plants expressing V. aconitifolia wild-type P5CS. This difference was further increased in plants treated with 200 mm NaCl. These results demonstrated that the feedback regulation of P5CS plays a role in controlling the level of Pro in plants under both normal and stress conditions. The elevated Pro also reduced free radical levels in response to osmotic stress, as measured by malondialdehyde production, and significantly improved the ability of the transgenic seedlings to grow in medium containing up to 200 mm NaCl. These findings shed new light on the regulation of Pro biosynthesis in plants and the role of Pro in reducing oxidative stress induced by osmotic stress, in addition to its accepted role as an osmolyte.
The Expression of D-Cyclin Genes Defines Distinct Developmental Zones in Snapdragon Apical Meristems and Is Locally Regulated by the Cycloidea Gene
Authors: Gaudin Valérie , Lunness Patricia A. , Fobert Pierre R. , Towers Matthew , Riou-Khamlichi Catherine , Murray James A.H. , Coen Enrico , Doonan John H. 
Published: July 2002

Abstract
Three D-cyclin genes are expressed in the apical meristems of snapdragon (Antirrhinum majus). The cyclin D1 andD3b genes are expressed throughout meristems, whereascyclin D3a is restricted to the peripheral region of the meristem, especially the organ primordia. During floral development,cyclin D3b expression is: (a) locally modulated in the cells immediately surrounding the base of organ primordia, defining a zone between lateral organs that may act as a developmental boundary; (b) locally modulated in the ventral petals during petal folding; and (c) is specifically repressed in the dorsal stamen by thecycloidea gene. Expression of both cyclin D3 genes is reduced prior to the cessation of cell cycle activity, as judged by histone H4 expression. Expression of all three D-cyclin genes is modulated by factors that regulate plant growth, particularly sucrose and cytokinin. These observations may provide a molecular basis for understanding the local regulation of cell proliferation during plant growth and development.
The Plastidic Phosphoglucomutase from Arabidopsis. A Reversible Enzyme Reaction with an Important Role in Metabolic Control
Authors: Periappuram Cyril , Steinhauer Lee , Barton Dennis L. , Taylor David C. , Chatson Brock , Zou Jitao 
Published: July 2002

Abstract
An Arabidopsis cDNA (AtPGMp) encoding the plastidic phosphoglucomutase (PGM) predicted a 623-amino acid protein with an N-terminal sequence typical of a plastid signal peptide. Expression of a recombinant protein inEscherichia coli confirmed its enzyme activity. The recombinant enzyme had an apparent K m value of 98.5 μm and a V max of 4.48 μmol min−1 (mg protein)−1. The Calvin cycle intermediates fructose-1,6-bisphosphate and ribulose-1,5-bisphosphate exerted an inhibitory effect on PGM activity, supporting its proposed involvement in controlling photosynthetic carbon flow. A point mutation was identified in the AtPGMp gene of the Arabidopsis pgm-1 mutant. The mutation in the mutant transcript generated a stop codon at about one third of the wild-type open reading frame, and thus rendered the polypeptide nonfunctional. Storage lipid analysis of the pgm-1 mutant seeds showed a 40% reduction in oil content compared with that of wild type. Our results indicate that plastidic PGM is an important factor affecting carbon flux in triacylglycerol accumulation in oilseed plants, most likely through its essential role in starch synthesis.
Fruit-Localized Phytochromes Regulate Lycopene Accumulation Independently of Ethylene Production in Tomato
Authors: Alba Rob , Cordonnier-Pratt Marie-Michèle , Pratt Lee H. 
Published: July 2002

Abstract
We show that phytochromes modulate differentially various facets of light-induced ripening of tomato fruit (Solanum lycopersicum L.). Northern analysis demonstrated that phytochrome A mRNA in fruit accumulates 11.4-fold during ripening. Spectroradiometric measurement of pericarp tissues revealed that the red to far-red ratio increases 4-fold in pericarp tissues during ripening from the immature-green to the red-ripe stage. Brief red-light treatment of harvested mature-green fruit stimulated lycopene accumulation 2.3-fold during fruit development. This red-light-induced lycopene accumulation was reversed by subsequent treatment with far-red light, establishing that light-induced accumulation of lycopene in tomato is regulated by fruit-localized phytochromes. Red-light and red-light/far-red-light treatments during ripening did not influence ethylene production, indicating that the biosynthesis of this ripening hormone in these tissues is not regulated by fruit-localized phytochromes. Compression analysis of fruit treated with red light or red/far-red light indicated that phytochromes do not regulate the rate or extent of pericarp softening during ripening. Moreover, treatments with red or red/far-red light did not alter the concentrations of citrate, malate, fructose, glucose, or sucrose in fruit. These results are consistent with two conclusions: (a) fruit-localized phytochromes regulate light-induced lycopene accumulation independently of ethylene biosynthesis; and (b) fruit-localized phytochromes are not global regulators of ripening, but instead regulate one or more specific components of this developmental process.