bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of Acyltransferase Activity in Immature Maize Embryos by Abscisic Acid and the Osmotic Environment
Authors: Pacheco-Moises F. , Valencia-Turcotte L. , Altuzar-Martinez M. , Rodriguez-Sotres R. 
Published: July 2002

Abstract
Maize (Zea mays L.) embryos, isolated from the developing seed and incubated in dilute buffer, show reduced triacylglycerol (TAG) synthesis, and accumulation stops after 24 h. Synthesis and accumulation can be maintained at high levels if the incubation medium contains abscisic acid (ABA) and/or a high osmotic concentration. Radiolabeled free fatty acids accumulate at higher levels in embryos that contain less TAG, and acetyl coenzyme A carboxylase activity remains essentially unchanged under all of the conditions tested. In contrast, the activities of the acyltransferases required for TAG synthesis remain high only in embryos incubated with ABA and/or a high osmotic concentration. Dose-response curves showed that 4 [mu]M of ABA or mannitol at -1.0 MPa elicits a full response; both values are within the range considered to be physiological. The TAG synthesis capacity and diacylglycerol acyltransferases activity lost by pretreatment of the embryos can be restored by re-exposure to ABA or high osmoticum. Germination is not involved because isolated scutellum halves showed the same changes in enzyme activity found in the whole embryo but did not germinate. Our results provide direct evidence for the regulation of TAG-synthesizing activities in maize embryos by ABA and the osmotic potential of the environment.
PNZIP Is a Novel Mesophyll-Specific cDNA That Is Regulated by Phytochrome and a Circadian Rhythm and Encodes a Protein with a Leucine Zipper Motif1
Authors: Chao Zheng Cheng , Porat Ron , Lu Pengzhe , Neill Sharman D. O' 
Published: July 2002

Abstract
We isolated and characterized a novel light-regulated cDNA from the short-day plant Pharbitis nil that encodes a protein with a leucine (Leu) zipper motif, designated PNZIP(Pharbitisnil Leu zipper). The PNZIP cDNA is not similar to any other gene with a known function in the database, but it shares high sequence homology with an Arabidopsis expressed sequence tag and to two other sequences of unknown function from the cyanobacteriumSynechocystis spp. and the red alga Porphyra purpurea, which together define a new family of evolutionarily conserved Leu zipper proteins. PNZIP is a single-copy gene that is expressed specifically in leaf photosynthetically active mesophyll cells but not in other nonphotosynthetic tissues such as the epidermis, trichomes, and vascular tissues. When plants were exposed to continuous darkness, PNZIP exhibited a rhythmic pattern of mRNA accumulation with a circadian periodicity of approximately 24 h, suggesting that its expression is under the control of an endogenous clock. However, the expression of PNZIP was unusual in that darkness rather than light promoted its mRNA accumulation. Accumulation of PNZIP mRNA during the dark is also regulated by phytochrome, since a brief exposure to red light in the middle of the night reduced its mRNA levels. Moreover, a far-red-light treatment at the end of day also reducedPNZIP mRNA accumulation during the dark, and that effect could be inhibited by a subsequent exposure to red light, showing the photoreversible response attributable to control through the phytochrome system.
Short-Lived and Phosphorylated Proteins Contribute to Carrier-Mediated Efflux, but Not to Influx, of Auxin in Suspension-Cultured Tobacco Cells1
Authors: Delbarre Alain , Muller Philippe , Guern Jean 
Published: July 2002

Abstract
Auxin is transported across the plasma membrane of plant cells by diffusion and by two carriers operating in opposite directions, the influx and efflux carriers. Both carriers most likely play an important role in controlling auxin concentration and distribution in plants but little is known regarding their regulation. We describe the influence of modifications of the transmembrane pH gradient and the effect of agents interfering with protein synthesis, protein traffic, and protein phosphorylation on the activity of the auxin carriers in suspension-cultured tobacco (Nicotiana tabacum L.) cells. Carrier-mediated influx and efflux were monitored independently by measuring the accumulation of [14C]2,4-dichlorophenoxyacetic acid and [3H]naphthylacetic acid, respectively. The activity of the influx carrier decreased on increasing external pH and on decreasing internal pH, whereas that of the efflux carrier was only impaired on internal acidification. The efflux carrier activity was inhibited by cycloheximide, brefeldin A, and the protein kinase inhibitors staurosporine and K252a, as shown by the increased capability of treated cells to accumulate [3H]naphthylacetic acid. Kinetics and reversibility of the effect of brefeldin A were consistent with one or several components of the efflux system being turned over at the plasma membrane with a half-time of less than 10 min. Inhibition of efflux by protein kinase inhibitors suggested that protein phosphorylation was essential to sustain the activity of the efflux carrier. On the contrary, the pharmacological agents used in this study failed to inhibit [14C]2,4-dichlorophenoxyacetic acid accumulation, suggesting that rapidly turned-over proteins or proteins activated by phosphorylation are not essential to carrier-mediated auxin influx. Our data support the idea that the efflux carrier in plants constitutes a complex system regulated at multiple levels, in marked contrast with the influx carrier. Physiological implications of the kinetic features of this regulation are discussed.
Heterogeneity and Photoinhibition of Photosystem II Studied with Thermoluminescence1
Authors: Andrée Simone , Weis Engelbert , Krieger Anja 
Published: July 2002

AbstractThermoluminescence (TL) signals were recorded from grana stacks, margins, and stroma lamellae from fractionated, dark-adapted thylakoid membranes of spinach (Spinacia oleracea L.) in the absence and in the presence of 2,6-dichlorphenylindophenol (DCMU). In the absence of DCMU, the TL signal from grana fractions consisted of a homogenous B-band, which originates from recombination of the semi-quinone QB− with the S2 state of the water-splitting complex and reflects active photosystem II (PSII). In the presence of DCMU, the B-band was replaced by the Q-band, which originates from an S2QA−recombination. Margin fractions mainly showed two TL-bands, the B- and C-bands, at approximately 50°C in the absence of DCMU, and Q- and C-bands in the presence of DCMU. The C-band is ascribed to a TyrD+-QA−recombination. In the absence of DCMU, the fractions of stromal lamellae mainly gave rise to a TL emission at 42°C. The intensity of this band was independent of the number of excitation flashes and was shifted to higher temperatures (52°C) after the addition of DCMU. Based on these observations, this band was considered to be a C-band. After photoinhibitory light treatment of uncoupled thylakoid membranes, the TL intensities of the B- and Q-bands decreased, whereas the intensity at 45°C (C-band) slightly increased. It is proposed that the 42 to 52°C band that was observed in marginal and stromal lamellae and in photoinhibited thylakoid membranes reflects inactive PSII centers that are assumed to be equivalent to inactive PSII QB-nonreducing centers.
Expression and Localization of Phosphoenolpyruvate Carboxylase in Developing and Germinating Wheat Grains1
Authors: González Marı́a-Cruz , Osuna Lidia , Echevarrı́a Cristina , Vidal Jean , Cejudo Francisco J. 
Published: July 2002

AbstractPhosphoenolpyruvate carboxylase (PEPC) activity and corresponding mRNA levels were investigated in developing and germinating wheat (Triticum aestivum) grains. During grain development PEPC activity increased to reach a maximum 15 d postanthesis. Western-blot experiments detected two main PEPC polypeptides with apparent molecular masses of 108 and 103 kD. The most abundant 103-kD PEPC subunit remained almost constant throughout the process of grain development and in the scutellum and aleurone layer of germinating grains. The less-abundant 108-kD polypeptide progressively disappeared during the second half of grain development and was newly synthesized in the scutellum and aleurone layer of germinating grains. PEPC mRNA was detected throughout the process of grain development; however, in germinating grains PEPC mRNA accumulated transiently in the scutellum and aleurone layer, showing a sharp maximum 24 h after imbibition. Immunolocalization studies revealed the presence of the enzyme in tissues with a high metabolic activity, as well as in the vascular tissue of the crease area of developing grains. A clear increase in PEPC was observed in the scutellar epithelium of grains 24 h after imbibition. The data suggest that the transiently formed PEPC mRNA in the scutellar epithelium encodes the 108-kD PEPC subunit.
Saline Stress Alters the Temporal Patterns of Xylem Differentiation and Alternative Oxidase Expression in Developing Soybean Roots1
Authors: Hilal Mirna , Zenoff Ana M. , Ponessa Graciela , Moreno Hortensia , Massa Eddy M. 
Published: July 2002

Abstract
We conducted a coordinated biochemical and morphometric analysis of the effect of saline conditions on the differentiation zone of developing soybean (Glycine max L.) roots. Between d 3 and d 14 for seedlings grown in control or NaCl-supplemented medium, we studied (a) the temporal evolution of the respiratory alternative oxidase (AOX) capacity in correlation with the expression and localization of AOX protein analyzed by tissue-print immunoblotting; (b) the temporal evolution and tissue localization of a peroxidase activity involved in lignification; and (c) the structural changes, visualized by light microscopy and quantified by image digitization. The results revealed that saline stress retards primary xylem differentiation. There is a corresponding delay in the temporal pattern of AOX expression, which is consistent with the xylem-specific localization of AOX protein and the idea that this enzyme is linked to xylem development. An NaCl-induced acceleration of the development of secondary xylem was also observed. However, the temporal pattern of a peroxidase activity localized in the primary and secondary xylem was unaltered by NaCl treatment. Thus, the NaCl-stressed root was specifically affected in the temporal patterns of AOX expression and xylem development.
Does Leaf Position within a Canopy Affect Acclimation of Photosynthesis to Elevated CO2?1
Authors: Osborne Colin P. , Roche Julie La , Garcia Richard L. , Kimball Bruce A. , Wall Gerard W. , Pinter Paul J. , Morte Robert L. La , Hendrey George R. , Long Steve P. 
Published: July 2002

Abstract
Previous studies of photosynthetic acclimation to elevated CO2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation in a vertical profile of leaves through a canopy of wheat (Triticum aestivum L.). The crop was grown at an elevated CO2 partial pressure of 55 Pa within a replicated field experiment using free-air CO2 enrichment. Gas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of ribulose-1,5-bisphosphate-limited photosynthesis. Net photosynthetic CO2 uptake was measured for leaves in situ within the canopy. Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2 uptake remained higher under elevated CO2. Acclimation at elevated CO2 was accompanied by decreases in both Rubisco and total leaf N contents and an increase in LHC content. Elevated CO2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO2 therefore depended on both vertical position within the canopy and the developmental stage.
The Boron Requirement and Cell Wall Properties of Growing and Stationary Suspension-CulturedChenopodium album L. Cells1
Authors: Fleischer Axel , Titel Christine , Ehwald Rudolf 
Published: July 2002

Abstract
Suspension-culturedChenopodium album L. cells are capable of continuous, long-term growth on a boron-deficient medium. Compared with cultures grown with boron, these cultures contained more enlarged and detached cells, had increased turbidity due to the rupture of a small number of cells, and contained cells with an increased cell wall pore size. These characteristics were reversed by the addition of boric acid (≥7 μm) to the boron-deficient cells. C. albumcells grown in the presence of 100 μm boric acid entered the stationary phase when they were not subcultured, and remained viable for at least 3 weeks. The transition from the growth phase to the stationary phase was accompanied by a decrease in the wall pore size. Cells grown without boric acid or with 7 μm boric acid were not able to reduce their wall pore size at the transition to the stationary phase. These cells could not be kept viable in the stationary phase, because they continued to expand and died as a result of wall rupture. The addition of 100 μm boric acid prevented wall rupture and the wall pore size was reduced to normal values. We conclude that boron is required to maintain the normal pore structure of the wall matrix and to mechanically stabilize the wall at growth termination.
Systematic Reverse Genetics of Transfer-DNA-Tagged Lines of Arabidopsis
Authors: Winkler Rodney G. , Frank Michael R. , Galbraith David W. , Feyereisen René , Feldmann Kenneth A. 
Published: July 2002

Abstract
We have developed an efficient reverse-genetics protocol that uses expedient pooling and hybridization strategies to identify individual transfer-DNA insertion lines from a collection of 6000 independently transformed lines in as few as 36 polymerase chain reactions. We have used this protocol to systematically isolate Arabidopsis lines containing insertional mutations in individual cytochrome P450 genes. In higher plants P450 genes encode enzymes that perform an exceptionally wide range of functions, including the biosynthesis of primary metabolites necessary for normal growth and development, the biosynthesis of secondary products, and the catabolism of xenobiotics. Despite their importance, progress in assigning enzymatic function to individual P450 gene products has been slow. Here we report the isolation of the first 12 such lines, including one (CYP83B1-1) that displays a runt phenotype (small plants with hooked leaves), and three insertions in abundantly expressed genes. The DNAs used in this study are publicly available and can be used to systematically isolate mutants in Arabidopsis.
Potentiation of the Oxidative Burst and Isoflavonoid Phytoalexin Accumulation by Serine Protease Inhibitors
Authors: Guo Ze-Jian , Lamb Chris , Dixon Richard A. 
Published: July 2002

AbstractTreatment of soybean (Glycine max L. cv Williams 82) cell-suspension cultures withPseudomonas syringae pv glycinea(Psg) harboring an avirulence gene (avrA) or with yeast elicitor resulted in an oxidative burst characterized by the accumulation of H2O2. This burst, and the resultant induction of glutathione S-transferase transcripts, occurred more rapidly and was more prolonged if cells were simultaneously treated with serine protease inhibitors such as phenylmethylsulfonyl fluoride (PMSF) or diisopropylfluorophosphate. PMSF and diisopropylfluorophosphate potentiate a large oxidative burst in cells exposed to Psg harboring theavrC avirulence gene, which is not recognized by the soybean cultivar used in this study. The potentiated burst was inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase, and by the protein kinase inhibitor K252a. PMSF treatment of elicited cells or cells exposed to Psg:avrA caused a large increase in the accumulation of the isoflavonoid phytoalexin glyceollin; however, this was not associated with increased levels of transcripts encoding key phytoalexin biosynthetic enzymes. Glyceollin accumulation was inhibited by diphenylene iodonium; however, the oxidative burst in cells treated with Psg:avrC and PMSF was not followed by phytoalexin accumulation. We conclude that active oxygen species from the oxidative burst are necessary but not sufficient for inducing isoflavonoid phytoalexin accumulation in soybean cells.
Age-Induced Protein Modifications and Increased Proteolysis in Potato Seed-Tubers1
Authors: Kumar G.N. Mohan , Houtz Robert L. , Knowles N. Richard 
Published: July 2002

Abstract
Long-term aging of potato (Solanum tuberosum) seed-tubers resulted in a loss of patatin (40 kD) and a cysteine-proteinase inhibitor, potato multicystatin (PMC), as well as an increase in the activities of 84-, 95-, and 125-kD proteinases. Highly active, additional proteinases (75, 90, and 100 kD) appeared in the oldest tubers. Over 90% of the total proteolytic activity in aged tubers was sensitive totrans-epoxysuccinyl-l-leucylamido (4-guanidino) butane or leupeptin, whereas pepstatin was the most effective inhibitor of proteinases in young tubers. Proteinases in aged tubers were also inhibited by crude extracts or purified PMC from young tubers, suggesting that the loss of PMC was responsible for the age-induced increase in proteinase activity. Nonenzymatic oxidation, glycation, and deamidation of proteins were enhanced by aging. Aged tubers developed “daughter” tubers that contained 3-fold more protein than “mother” tubers, with a polypeptide profile consistent with that of young tubers. Although PMC and patatin were absent from the older mother tubers, both proteins were expressed in the daughter tubers, indicating that aging did not compromise the efficacy of genes encoding PMC and patatin. Unlike the mother tubers, proteinase activity in daughter tubers was undetectable. Our results indicate that tuber aging nonenzymatically modifies proteins, which enhances their susceptibility to breakdown; we also identify a role for PMC in regulating protein turnover in potato tubers.
Purification and cDNA Cloning of Isochorismate Synthase from Elicited Cell Cultures of Catharanthus roseus
Authors: van Tegelen Léon J.P. , Moreno Paolo R.H. , Croes Anton F. , Verpoorte Robert , Wullems George J. 
Published: July 2002

Abstract
Isochorismate is an important metabolite formed at the end of the shikimate pathway, which is involved in the synthesis of both primary and secondary metabolites. It is synthesized from chorismate in a reaction catalyzed by the enzyme isochorismate synthase (ICS; EC 5.4.99.6). We have purified ICS to homogeneity from elicited Catharanthus roseus cell cultures. Two isoforms with an apparent molecular mass of 64 kD were purified and characterized. The Km values for chorismate were 558 and 319 μm for isoforms I and II, respectively. The isoforms were not inhibited by aromatic amino acids and required Mg2+ for enzyme activity. Polymerase chain reaction on a cDNA library from elicited C. roseus cells with a degenerated primer based on the sequence of an internal peptide from isoform II resulted in an amplification product that was used to screen the cDNA library. This led to the first isolation, to our knowledge, of a plant ICS cDNA. The cDNA encodes a protein of 64 kD with an N-terminal chloroplast-targeting signal. The deduced amino acid sequence shares homology with bacterial ICS and also with anthranilate synthases from plants. Southern analysis indicates the existence of only one ICS gene in C. roseus.
Use of Ubiquitin Fusions to Augment Protein Expression in Transgenic Plants1
Authors: Hondred David , Walker Joseph M. , Mathews Dennis E. , Vierstra Richard D. 
Published: July 2002

Abstract
A major goal of plant biotechnology is the production of genetically engineered crops that express natural or foreign proteins at high levels. To enhance protein accumulation in transgenic plants, we developed a set of vectors that express proteins and peptides as C-terminal translational fusions with ubiquitin (UBQ). Studies of several proteins in tobacco (Nicotiana tabacum) showed that: (a) proteins can be readily expressed in plants as UBQ fusions; (b) by the action of endogenous UBQ-specific proteases (Ubps), these fusions are rapidly and precisely processed in vivo to release the fused protein moieties in free forms; (c) the synthesis of a protein as a UBQ fusion can significantly augment its accumulation; (d) proper processing and localization of a protein targeted to either the apoplast or the chloroplast is not affected by the N-terminal UBQ sequence; and (e) single amino acid substitutions surrounding the cleavage site can inhibit in vivo processing of the fusion by Ubps. Noncleavable UBQ fusions of β-glucuronidase became extensively modified, with additional UBQs in planta. Because multiubiquitinated proteins are the preferred substrates of the 26S proteasome, noncleavable fusions may be useful for decreasing protein half-life. Based on their ability to augment protein accumulation and the sequence specificity of Ubps, UBQ fusions offer a versatile way to express plant proteins.
The Arabidopsis dwarf1 Mutant Is Defective in the Conversion of 24-Methylenecholesterol to Campesterol in Brassinosteroid Biosynthesis1
Authors: Choe Sunghwa , Dilkes Brian P. , Gregory Brian D. , Ross Amanda S. , Yuan Heng , Noguchi Takahiro , Fujioka Shozo , Takatsuto Suguru , Tanaka Atsushi , Yoshida Shigeo , Tax Frans E. , Feldmann Kenneth A. 
Published: July 2002

Abstract
Since the isolation and characterization of dwarf1-1 (dwf1-1) from a T-DNA insertion mutant population, phenotypically similar mutants, including deetiolated2 (det2),constitutive photomorphogenesis and dwarfism(cpd), brassinosteroid insensitive1 (bri1), and dwf4, have been reported to be defective in either the biosynthesis or the perception of brassinosteroids. We present further characterization ofdwf1-1 and additional dwf1 alleles. Feeding tests with brassinosteroid-biosynthetic intermediates revealed that dwf1 can be rescued by 22α-hydroxycampesterol and downstream intermediates in the brassinosteroid pathway. Analysis of the endogenous levels of brassinosteroid intermediates showed that 24-methylenecholesterol in dwf1 accumulates to 12 times the level of the wild type, whereas the level of campesterol is greatly diminished, indicating that the defective step is in C-24 reduction. Furthermore, the deduced amino acid sequence of DWF1 shows significant similarity to a flavin adenine dinucleotide-binding domain conserved in various oxidoreductases, suggesting an enzymatic role for DWF1. In support of this, 7 of 10 dwf1 mutations directly affected the flavin adenine dinucleotide-binding domain. Our molecular characterization of dwf1 alleles, together with our biochemical data, suggest that the biosynthetic defect indwf1 results in reduced synthesis of bioactive brassinosteroids, causing dwarfism.