bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Nitrate-Inducible Ferredoxin in Maize Roots (Genomic Organization and Differential Expression of Two Nonphotosynthetic Ferredoxin Isoproteins)
Authors: Matsumura T. , Sakakibara H. , Nakano R. , Kimata Y. , Sugiyama T. , Hase T. 
Published: July 2002

Abstract
We have identified and characterized a nitrate-inducible ferredoxin (Fd) in maize (Zea mays L.) roots by structural analysis of the purified protein and by cloning of its cDNA and gene. In maize Fd isoproteins are encoded by a small multigene family, and the nitrate-inducible Fd was identified as a novel isoprotein, designated Fd VI, which differed from any Fd I to Fd V identified to date. In the roots of seedlings cultured without nitrate, Fd VI was undetectable. However, during the induction of the capacity for nitrate assimilation, the amount of Fd VI increased markedly within 24 h. Concurrently, the level of transcript for Fd VI increased, but more quickly, reaching a maximal level within 2 h with kinetics similar to those of nitrite reductase and Fd-NADP+ reductase. Fd III was constitutively expressed in roots, and no such changes at the protein and mRNA levels were observed during the nitrate induction. In the 5[prime] flanking region of the gene for Fd VI only, we identified NIT-2 motifs, which are widely found in genes for enzymes related to nitrogen metabolism. These data indicate that Fd VI is co-induced with the previously characterized enzymes involved in nitrate assimilation, and they suggest that the novel Fd isoprotein, distinct from the constitutively expressed Fd, might play an important role as an electron carrier from NADPH to nitrite reductase and other Fd-dependent enzymes in root plastids.
L-Ascorbic Acid Metabolism in the Ascorbate-Deficient Arabidopsis Mutant vtc1
Authors: Conklin P. L. , Pallanca J. E. , Last R. L. , Smirnoff N. 
Published: July 2002

Abstract
The biosynthesis of L-ascorbic acid (vitamin C) is not well understood in plants. The ozone-sensitive Arabidopsis thaliana mutant vitamin c-1 (vtc1; formerly known as soz1) is deficient in ascorbic acid, accumulating approximately 30% of wild-type levels. This deficiency could result from elevated catabolism or decreased biosynthesis. No differences that could account for the deficiency were found in the activities of enzymes that catalyze the oxidation or reduction of ascorbic acid. The absolute rate of ascorbic acid turnover is actually less in vtc1 than in wild type; however, the turnover rate relative to the pool of ascorbic acid is not significantly different. The results from [U-14C]Glc labeling experiments suggest that the deficiency is the result of a biosynthetic defect: less L-[14C]ascorbic acid as a percentage of total soluble 14C accumulates in vtc1 than in wild type. The feeding of two putative biosynthetic intermediates, D-glucosone and L-sorbosone, had no positive effect on ascorbic acid levels in either genotype. The vtc1 defect does not appear to be the result of a deficiency in L-galactono-1,4-lactone dehydrogenase, an enzyme able to convert L-galactono-1,4-lactone to ascorbic acid.
Reduction of Light-Induced Anthocyanin Accumulation in Inoculated Sorghum Mesocotyls1
Authors: Lo Sze-Chung Clive , Nicholson Ralph L. 
Published: July 2002

Abstract
Sorghum (Sorghum bicolor L. Moench) accumulates the anthocyanin cyanidin 3-dimalonyl glucoside in etiolated mesocotyls in response to light. Inoculation with the nonpathogenic fungus Cochliobolus heterostrophus drastically reduced the light-induced accumulation of anthocyanin by repressing the transcription of the anthocyanin biosynthesis genes encoding flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase. In contrast to these repression effects, fungal inoculation resulted in the synthesis of the four known 3-deoxyanthocyanidin phytoalexins and a corresponding activation of genes encoding the key branch-point enzymes in the phenylpropanoid pathway, phenylalanine ammonia-lyase and chalcone synthase. In addition, a gene encoding the pathogenesis-related protein PR-10 was strongly induced in response to inoculation. The accumulation of phytoalexins leveled off by 48 h after inoculation and was accompanied by a more rapid increase in the rate of anthocyanin accumulation. The results suggest that the plant represses less essential metabolic activities such as anthocyanin synthesis as a means of compensating for the immediate biochemical and physiological needs for the defense response.
Purification and Characterization of Peroxidases Correlated with Lignification in Poplar Xylem1
Authors: Christensen Jørgen Holst , Bauw Guy , Gjesing Welinder Karen , Van Montagu Marc , Boerjan Wout 
Published: July 2002

Abstract
Lignin is an integral cell wall component of all vascular plants. Peroxidases are widely believed to catalyze the last enzymatic step in the biosynthesis of lignin, the dehydrogenation of the p-coumaryl alcohols. As the first stage in identifying lignin-specific peroxidase isoenzymes, the classical anionic peroxidases found in the xylem of poplar (Populus trichocarpa Trichobel) were purified and characterized. Five different poplar xylem peroxidases (PXP 1, PXP 2, PXP 3–4, PXP 5, and PXP 6) were isolated. All five peroxidases were strongly glycosylated (3.6% to 4.9% N-glucosamine), with apparent molecular masses between 46 and 54 kD and pI values between pH 3.1 and 3.8. Two of the five isolated peroxidases (PXP 3–4 and PXP 5) could oxidize the lignin monomer analog syringaldazine, an activity previously correlated with lignification in poplar. Because these isoenzymes were specifically or preferentially expressed in xylem, PXP 3–4 and PXP 5 are suggested to be involved in lignin polymerization.
Rapid Regulation by Acid pH of Cell Wall Adjustment and Leaf Growth in Maize Plants Responding to Reversal of Water Stress
Authors: Bogoslavsky Lev , Neumann Peter M. 
Published: July 2002

Abstract
The role of acid secretion in regulating short-term changes in growth rate and wall extensibility was investigated in emerging first leaves of intact, water-stressed maize (Zea mays L.) seedlings. A novel approach was used to measure leaf responses to injection of water or solutions containing potential regulators of growth. Both leaf elongation and wall extensibility, as measured with a whole-plant creep extensiometer, increased dramatically within minutes of injecting water, 0.5 mm phosphate, or strong (50 mm) buffer solutions with pH ≤ 5.0 into the cell-elongation zone of water-stressed leaves. In contrast, injecting buffer solutions at pH ≥ 5.5 inhibited these fast responses. Solutions containing 0.5 mm orthovanadate or erythrosin B to inhibit wall acidification by plasma membrane H+-ATPases were also inhibitory. Thus, cell wall extensibility and leaf growth in water-stressed plants remained inhibited, despite the increased availability of (injected) water when accompanying increases in acid-induced wall loosening were prevented. However, growth was stimulated when pH 4.5 buffers were included with the vanadate injections. These findings suggest that increasing the availability of water to expanding cells in water-stressed leaves signals rapid increases in outward proton pumping by plasma membrane H+-ATPases. Resultant increases in cell wall extensibility participate in the regulation of water uptake, cell expansion, and leaf growth.
Myo-Inositol-Dependent Sodium Uptake in Ice Plant1
Authors: Nelson Donald E. , Koukoumanos Michelle , Bohnert Hans J. 
Published: July 2002

Abstract
In salt-stressed ice plants (Mesembryanthemum crystallinum), sodium accumulates to high concentrations in vacuoles, and polyols (myo-inositol,d-ononitol, and d-pinitol) accumulate in the cytosol. Polyol synthesis is regulated by NaCl and involves induction and repression of gene expression (D.E. Nelson, B. Shen, and H.J. Bohnert [1998] Plant Cell 10: 753–764). In the study reported here we found increased phloem transport of myo-inositol and reciprocal increased transport of sodium and inositol to leaves under stress. To determine the relationship between increased translocation and sodium uptake, we analyzed the effects of exogenous application of myo-inositol: The NaCl-inducible ice plant myo-inositol 1-phosphate synthase is repressed in roots, and sodium uptake from root to shoot increases without stimulating growth. Sodium uptake and transport through the xylem was coupled to a 10-fold increase of myo-inositol and ononitol in the xylem. Seedlings of the ice plant are not salt-tolerant, and yet the addition of exogenousmyo-inositol conferred upon them patterns of gene expression and polyol accumulation observed in mature, salt-tolerant plants. Sodium uptake and transport through the xylem was enhanced in the presence of myo-inositol. The results indicate an interdependence of sodium uptake and alterations in the distribution ofmyo-inositol. We hypothesize thatmyo-inositol could serve not only as a substrate for the production of compatible solutes but also as a leaf-to-root signal that promotes sodium uptake.
An in Vitro System from Maize Seedlings for Tryptophan-Independent Indole-3-Acetic Acid Biosynthesis1
Authors: Östin Anders , Ilić Nebojsa , Cohen Jerry D. 
Published: July 2002

Abstract
The enzymatic synthesis of indole-3-acetic acid (IAA) from indole by an in vitro preparation from maize (Zea mays L.) that does not use tryptophan (Trp) as an intermediate is described. Light-grown seedlings of normal maize and the maize mutant orange pericarp were shown to contain the necessary enzymes to convert [14C]indole to IAA. The reaction was not inhibited by unlabeled Trp and neither [14C]Trp nor [14C]serine substituted for [14C]indole in this in vitro system. The reaction had a pH optimum greater than 8.0, required a reducing environment, and had an oxidation potential near that of ascorbate. The results obtained with this in vitro enzyme preparation provide strong, additional evidence for the presence of a Trp-independent IAA biosynthesis pathway in plants.
γ-Radiation Induces Leaf Trichome Formation in Arabidopsis1
Authors: Nagata Toshifumi , Todoriki Setsuko , Hayashi Toru , Shibata Yuriko , Mori Masaki , Kanegae Hiromi , Kikuchi Shoshi 
Published: July 2002

Abstract
We observed induction of additional trichome formation on the adaxial surface of mature leaves of Arabidopsis after massive doses (1–3 kilograys) of γ-radiation from cobalt-60. A typical increase in trichome number was observed in the seventh leaf when the full expansion of the fifth leaf was irradiated. Under normal growth conditions, trichome numbers on the adaxial surface of seventh leaf of the Arabidopsis ecotypes Columbia (Col) and Landsberg erecta (Ler) were 122.5 ± 22.7 and 57.5 ± 14.5, respectively. However, γ-radiation induced additional trichome formation and the numbers rose to 207.9 ± 43.7 and 95.0 ± 27.1 in Col and Ler, respectively. In Col the shape of new trichomes was intact and their formation was spatially maintained at equal distances from other trichomes. In Ler trichome morphology was aberrant and the formation was relatively random. Treatment with antioxidants before γ-irradiation suppressed the increase in trichome number, and treatment with methyl viologen and light induced small trichomes. These results suggest that γ-radiation-induced trichome formation is mediated by active oxygen species generated by water radiolysis. γ-Radiation-induced trichome formation was blocked in the trichome mutants ttg-1, gl1-1, andgl2-1. These results suggest that γ-radiation-induced trichome formation is mediated by the normal trichome developmental pathway.
Inhibition of Water Channels by HgCl2 in Intact Wheat Root Cells1
Authors: Zhang Wen-Hao , Tyerman Stephen D. 
Published: July 2002

Abstract
To assess the extent of water flow through channels in the membranes of intact higher plant cells, the effects of HgCl2 on hydraulic conductivity (LP) of wheat (Triticum aestivum L.) root cells were investigated using a pressure probe. The LP of root cells was reduced by 75% in the presence of 100 μm HgCl2. The K+-channel blocker tetraethylammonium had no effect on theLP at concentrations that normally block K+ channels. HgCl2 rapidly depolarized the membrane potential (Vm) of the root cells. The dose-response relationship of inhibition ofLP and depolarization ofVm were not significantly different, with half-maximal inhibition occurring at 4.6 and 7.8 μm, respectively. The inhibition of LP and the depolarization of Vm caused by HgCl2 were partially reversed by β-mercaptoethanol. The inhibition of LP by HgCl2 was similar in magnitude to that caused by hypoxia, and the addition of HgCl2 to hypoxia-treated cells did not result in further inhibition. We compared the LP of intact cells with that predicted from a model of cortical cells incorporating water flow across both the plasma membrane and the tonoplast using measured values of water permeability from isolated membranes, and found that HgCl2 has other effects in addition to the direct inhibition of water channels.
The arcelin-5 Gene of Phaseolus vulgarisDirects High Seed-Specific Expression in TransgenicPhaseolus acutifolius and Arabidopsis Plants1
Authors: Goossens Alain , Dillen Willy , De Clercq Janniek , Van Montagu Marc , Angenon Geert 
Published: July 2002

Abstract
The regulatory sequences of many genes encoding seed storage proteins have been used to drive seed-specific expression of a variety of proteins in transgenic plants. Because the levels at which these transgene-derived proteins accumulate are generally quite low, we investigated the utility of the arcelin-5 regulatory sequences in obtaining high seed-specific expression in transgenic plants. Arcelin-5 is an abundant seed protein found in some wild common bean (Phaseolus vulgaris L.) genotypes. Seeds of Arabidopsis and Tepary bean (Phaseolus acutifolius A. Gray) plants transformed with arcelin-5 gene constructs synthesized arcelin-5 to levels of 15% and 25% of the total protein content, respectively. To our knowledge, such high expression levels directed by a transgene have not been reported before. The transgenic plants also showed low plant-to-plant variation in arcelin expression. Complex transgene integration patterns, which often result in gene silencing effects, were not associated with reduced arcelin-5expression. High transgene expression was the result of high mRNA steady-state levels and was restricted to seeds. This indicates that all requirements for high seed-specific expression arecis elements present in the cloned genomicarcelin-5 sequence and trans-acting factors that are available in Arabidopsis and Phaseolusspp., and thus probably in most dicotyledonous plants.
Metabolite Control Overrides Circadian Regulation of Phosphoenolpyruvate Carboxylase Kinase and CO2 Fixation in Crassulacean Acid Metabolism
Authors: Borland Anne M. , Hartwell James , Jenkins Gareth I. , Wilkins Malcolm B. , Nimmo Hugh G. 
Published: July 2002

Abstract
Phosphoenolpyruvate carboxylase (PEPc) catalyzes the primary fixation of CO2 in Crassulacean acid metabolism plants. Flux through the enzyme is regulated by reversible phosphorylation. PEPc kinase is controlled by changes in the level of its translatable mRNA in response to a circadian rhythm. The physiological significance of changes in the levels of PEPc-kinase-translatable mRNA and the involvement of metabolites in control of the kinase was investigated by subjectingKalanchoë daigremontiana leaves to anaerobic conditions at night to modulate the magnitude of malate accumulation, or to a rise in temperature at night to increase the efflux of malate from vacuole to cytosol. Changes in CO2 fixation and PEPc kinase activity reflected those in kinase mRNA. The highest rates of CO2 fixation and levels of kinase mRNA were observed in leaves subjected to anaerobic treatment for the first half of the night and then transferred to ambient air. In leaves subjected to anaerobic treatment overnight and transferred to ambient air at the start of the day, PEPc-kinase-translatable mRNA and activity, the phosphorylation state of PEPc, and fixation of atmospheric CO2 were significantly higher than those for control leaves for the first 3 h of the light period. A nighttime temperature increase from 19°C to 27°C led to a rapid reduction in kinase mRNA and activity; however, this was not observed in leaves in which malate accumulation had been prevented by anaerobic treatment. These data are consistent with the hypothesis that a high concentration of malate reduces both kinase mRNA and the accumulation of the kinase itself.
Interaction Specificity of Arabidopsis Calcineurin B-Like Calcium Sensors and Their Target Kinases
Authors: Kim Kyung-Nam , Cheong Yong Hwa , Gupta Rajeev , Luan Sheng 
Published: July 2002

Abstract
Calcium is a critical component in a number of plant signal transduction pathways. A new family of calcium sensors called calcineurin B-like proteins (AtCBLs) have been recently identified from Arabidopsis. These calcium sensors have been shown to interact with a family of protein kinases (CIPKs). Here we report that each individual member of AtCBL family specifically interacts with a subset of CIPKs and present structural basis for the interaction and for the specificity underlying these interactions. Although the C-terminal region of CIPKs is responsible for interaction with AtCBLs, the N-terminal region of CIPKs is also involved in determining the specificity of such interaction. We have also shown that all three EF-hand motifs in AtCBL members are required for the interaction with CIPKs. Several AtCBL members failed to interact with any of the CIPKs presented in this study, suggesting that these AtCBL members either have other CIPKs as targets or they target distinct proteins other than CIPKs. These results may provide structural basis for the functional specificity of CBL family of calcium sensors and their targets.
Ion Channel-Forming Alamethicin Is a Potent Elicitor of Volatile Biosynthesis and Tendril Coiling. Cross Talk between Jasmonate and Salicylate Signaling in Lima Bean
Authors: Engelberth Jürgen , Koch Thomas , Schüler Göde , Bachmann Nadine , Rechtenbach Jana , Boland Wilhelm 
Published: July 2002

Abstract
Alamethicin (ALA), a voltage-gated, ion channel-forming peptide mixture from Trichoderma viride, is a potent elicitor of the biosynthesis of volatile compounds in lima bean (Phaseolus lunatus). Unlike elicitation with jasmonic acid or herbivore damage, the blend of substances emitted comprises only the two homoterpenes, 4,11-dimethylnona-1,3,7-triene and 4,8,12-trimethyltrideca-1,3,7,11-tetraene, and methyl salicylate. Inhibition of octadecanoid signaling by aristolochic acid and phenidone as well as mass spectrometric analysis of endogenous jasmonate demonstrate that ALA induces the biosynthesis of volatile compounds principally via the octadecanoid-signaling pathway (20-fold increase of jasmonic acid). ALA also up-regulates salicylate biosynthesis, and the time course of the production of endogenous salicylate correlates well with the appearance of the methyl ester in the gas phase. The massive up-regulation of the SA-pathway (90-fold) interferes with steps in the biosynthetic pathway downstream of 12-oxophytodienoic acid and thereby reduces the pattern of emitted volatiles to compounds previously shown to be induced by early octadecanoids. ALA also induces tendril coiling in various species like Pisum, Lathyrus, and Bryonia, but the response appears to be independent from octadecanoid biosynthesis, because inhibitors of lipoxygenase and phospholipase A2 do not prevent the coiling reaction.
Altered Patterns of Sucrose Synthase Phosphorylation and Localization Precede Callose Induction and Root Tip Death in Anoxic Maize Seedlings
Authors: Subbaiah Chalivendra C. , Sachs Martin M. 
Published: July 2002

Abstract
Root extracts made from maize (Zea mays) seedlings submerged for 2 h showed an increased 32P-labeling of a 90-kD polypeptide in a Ca2+-dependent manner. This protein was identified as sucrose synthase (SS) by immunoprecipitation and mutant analysis. Metabolic labeling with32Pi indicated that the aerobic levels of SS phosphorylation were maintained up to 2 h of anoxia. In contrast, during prolonged anoxia the protein was under-phosphorylated, and by 48 h most of the protein existed in the unphosphorylated form. In seedlings submerged for 2 h or longer, a part of SS became associated with the microsomal fraction and this membrane localization of SS was confined only to the root tip. This redistribution of SS in the root tip preceded callose induction, an indicator of cell death. The sh1 mutants showed sustained SS phosphorylation and lacked the anoxia-induced relocation of SS, indicating that it was the SH1 form of the enzyme that was redistributed during anoxia. Thesh1 mutants also showed less callose deposition and greater tolerance to prolonged anoxia than their non-mutant siblings. EGTA accentuated anoxic effects on membrane localization of SS and callose accumulation, whereas Ca2+ addition reversed the EGTA effects. These results indicate that the membrane localization of SS is an important early event in the anoxic root tip, probably associated with the differential anoxic tolerance of the two SS mutants. We propose that beside the transcriptional control of genes encoding SS, the reversible phosphorylation of SS provides a potent regulatory mechanism of sugar metabolism in response to developmental and environmental signals.
Altered Middle Lamella Homogalacturonan and Disrupted Deposition of (1→5)-α-l-Arabinan in the Pericarp ofCnr, a Ripening Mutant of Tomato
Authors: Orfila Caroline , Seymour Graham B. , Willats William G.T. , Huxham I. Max , Jarvis Michael C. , Dover Colin J. , Thompson Andrew J. , Knox J. Paul 
Published: July 2002

AbstractCnr (colorless non-ripening) is a pleiotropic tomato (Lycopersicon esculentum) fruit ripening mutant with altered tissue properties including weaker cell-to-cell contacts in the pericarp (A.J. Thompson, M. Tor, C.S. Barry, J. Vrebalov, C. Orfila, M.C. Jarvis, J.J. Giovannoni, D. Grierson, G.B. Seymour [1999] Plant Physiol 120: 383–390). Whereas the genetic basis of theCnr mutation is being identified by molecular analyses, here we report the identification of cell biological factors underlying the Cnr texture phenotype. In comparison with wild type, ripe-stage Cnr fruits have stronger, non-swollen cell walls (CW) throughout the pericarp and extensive intercellular space in the inner pericarp. Using electron energy loss spectroscopy imaging of calcium-binding capacity and anti-homogalacturonan (HG) antibody probes (PAM1 and JIM5) we demonstrate that maturation processes involving middle lamella HG are altered in Cnr fruit, resulting in the absence or a low level of HG-/calcium-based cell adhesion. We also demonstrate that the deposition of (1→5)-α-l-arabinan is disrupted in Cnr pericarp CW and that this disruption occurs prior to fruit ripening. The relationship between the disruption of (1→5)-α-l-arabinan deposition in pericarp CW and theCnr phenotype is discussed.