bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of Monoterpene Accumulation in Leaves of Peppermint
Authors: Gershenzon Jonathan , McConkey Marie E. , Croteau Rodney B. 
Published: July 2002

AbstractPlants synthesize numerous classes of natural products that accumulate during development and are thought to function as constitutive defenses against herbivores and pathogens. However, little information is available about how the levels of such defenses are regulated. We measured the accumulation of monoterpenes, a model group of constitutive defenses, in peppermint (Mentha ×piperita L.) leaves and investigated several physiological processes that could regulate their accumulation: the rate of biosynthesis, the rate of metabolic loss, and the rate of volatilization. Monoterpene accumulation was found to be restricted to leaves of 12 to 20 d of age, the period of maximal leaf expansion. The rate of monoterpene biosynthesis determined by14CO2 incorporation was closely correlated with monoterpene accumulation, as determined by gas chromatographic analysis, and appeared to be the principal factor controlling the monoterpene level of peppermint leaves. No significant catabolic losses of monoterpenes were detected throughout leaf development, and monoterpene volatilization was found to occur at a very low rate, which, on a monthly basis, represented less than 1% of the total pool of stored monoterpenes. The composition of volatilized monoterpenes differed significantly from that of the total plant monoterpene pool, suggesting that these volatilized products may arise from a separate secretory system. With the demonstration that the rate of biosynthesis is the chief process that determines monoterpene accumulation in peppermint, efforts to improve production in this species can now focus on the genes, enzymes, and cell differentiation processes that regulate monoterpene biosynthesis.
Developmental Regulation of Monoterpene Biosynthesis in the Glandular Trichomes of Peppermint
Authors: McConkey Marie E. , Gershenzon Jonathan , Croteau Rodney B. 
Published: July 2002

Abstract
Monoterpene production in peppermint (Mentha ×piperita L.) glandular trichomes is determined by the rate of biosynthesis, as determined by 14CO2incorporation, and is restricted to leaves 12 to 20 d of age. Using oil glands isolated from peppermint leaves of different ages, in vitro assay of the eight sequential enzymes responsible for the biosynthesis of the principal monoterpene (−)-menthol indicated that all but one biosynthetic enzyme had a very similar developmental profile. Activities were highest in leaves 12 to 20 d of age, with a sharp peak centered at 15 d. The exception, (−)-menthone reductase, the last enzyme of the pathway, exhibited a later peak of activity, which was centered at approximately 21 d. The correlation between in vitro enzyme activity and the rate of biosynthesis measured in vivo suggests that monoterpene formation is controlled mainly by the coordinately regulated activity of the relevant biosynthetic enzymes. Developmental immunoblotting of limonene synthase, which catalyzes the committed step of the pathway, demonstrated a direct correlation between enzyme activity and enzyme protein, suggesting that the dynamic time course for the remaining pathway enzyme activities also reflects the corresponding protein levels. RNA-blot analyses indicated that the genes encoding enzymes of the early pathway steps are transcriptionally activated in a coordinated fashion, with a time course superimposible with activity measurements and immunoblot data. These results demonstrating coincidental temporal changes in enzyme activities, enzyme protein level, and steady-state transcript abundances indicate that most of the monoterpene biosynthetic enzymes in peppermint are developmentally regulated at the level of gene expression.
Toward a Functional Catalog of the Plant Genome. A Survey of Genes for Lipid Biosynthesis
Authors: Mekhedov Sergei , de Ilárduya Oskar Martı́nez , Ohlrogge John 
Published: July 2002

Abstract
Public databases now include vast amounts of recently acquired DNA sequences that are only partially annotated and, furthermore, are often annotated by automated methods that are subject to errors. Maximum information value of these databases can be derived only by further detailed analyses that frequently require careful examination of records in the context of biological functions. In this study we present an example of such an analysis focused on plant glycerolipid synthesis. Public databases were searched for sequences corresponding to 65 plant polypeptides involved in lipid metabolism. Comprehensive search results and analysis of genes, cDNAs and expressed sequence tags (ESTs) are available online (http://www.canr.msu.edu/lgc). Multiple alignments provided a method to estimate the number of genes in gene families. Further analysis of sequences allowed us to tentatively identify several previously undescribed genes in Arabidopsis. For example, two genomic sequences were identified as candidates for the palmitate-specific monogalactosyldiacylglycerol desaturase (FAD5). A candidate genomic sequence for 3-ketoacyl-acyl-carrier protein (ACP) synthase involved in mitochondrial fatty acid biosynthesis was also identified. Biotin carboxyl carrier protein (BCCP) in Arabidopsis is encoded by at least two genes, but the most abundant BCCP transcript so far has not been characterized. The large number (&gt;165,000) of plant ESTs also provides an opportunity to perform “digital northern” comparisons of gene expression levels across many genes. EST abundance in general correlated with biochemical and flux characteristics of the enzymes in Arabidopsis leaf tissue. In a few cases, statistically significant differences in EST abundance levels were observed for enzymes that catalyze similar reactions in fatty acid metabolism. For example, ESTs for the FatB acyl-ACP thioesterase occur 21 times compared with 7 times for FatA acyl-ACP thioesterase, although flux through the FatA reaction is several times higher than through FatB. Such comparisons may provide initial clues toward previously undescribed regulatory phenomena. The abundance of ESTs for ACP compared with that of stearoyl-ACP desaturase and FatB acyl-ACP thioesterase suggests that concentrations of some enzymes of fatty acid synthesis may be higher than their acyl-ACP substrates.
Hypersensitivity of an Arabidopsis Sugar Signaling Mutant toward Exogenous Proline Application
Authors: Hellmann Hanjo , Funck Dietmar , Rentsch Doris , Frommer Wolf B. 
Published: July 2002

Abstract
In transgenic Arabidopsis a patatin class I promoter from potato is regulated by sugars and proline (Pro), thus integrating signals derived from carbon and nitrogen metabolism. In both cases a signaling cascade involving protein phosphatases is involved in induction. Other endogenous genes are also regulated by both Pro and carbohydrates. Chalcone synthase (CHS) gene expression is induced by both, whereas the Pro biosynthetic Δ1-pyrroline-5-carboxylate synthetase (P5CS) is induced by high Suc concentrations but repressed by Pro, and Pro dehydrogenase (ProDH) is inversely regulated. The mutantrsr1-1, impaired in sugar dependent induction of the patatin promoter, is hypersensitive to low levels of external Pro and develops autofluorescence and necroses. Toxicity of Pro can be ameliorated by salt stress and exogenously supplied metabolizable carbohydrates. The rsr1-1 mutant shows a reduced response regarding sugar induction of CHS andP5CS expression. ProDH expression is de-repressed in the mutant but still down-regulated by sugar. Pro toxicity seems to be mediated by the degradation intermediate Δ1-pyrroline-5-carboxylate. Induction of the patatin promoter by carbohydrates and Pro, together with the Pro hypersensitivity of the mutant rsr1-1, demonstrate a new link between carbon/nitrogen and stress responses.
Purification and Characterization of a Membrane-Associated 48-Kilodalton Phospholipase A2 in Leaves of Broad Bean
Authors: Jung Kwang Mook , Kim Dae Kyong 
Published: July 2002

Abstract
Several lines of evidence indicate that phospholipase A2 (PLA2) plays a crucial role in plant cellular responses through production of linolenic acid, the precursor of jasmonic acid, from membrane phospholipids. Here we report the purification and characterization of a 48-kD PLA2 from the membrane fractions of leaves of broad bean (Vicia faba). The plant PLA2 was purified to near homogeneity by sequential column chromatographies from the membrane extracts. The purified 48-kD protein migrated as a single band on a SDS-PAGE gel and its density correlated with the PLA2 activity. It was further confirmed that this 48-kD protein is the PLA2enzyme based on immunoprecipitating the activity with a monoclonal antibody against it and purifying the enzyme to homogeneity with the antibody affinity column. The purified plant PLA2 preferred 2-linolenoyl-sn-glycerol-3-phosphocholine (GPC) to 2-linoleoyl-GPC, 2-palmitoyl-GPC and 2-arachidonyl-GPC as substrates with a pH optimum at pH 7.0 to 8.0. The plant PLA2 was activated by calmodulin and inhibited by pretreatment of 5,8,11,14-eicosatetraynoic acid known as an inhibitor of mammalian PLA2s. The enzyme was characterized as a Ca2+-independent PLA2 different from mammalian PLA2s. This membrane-associated and Ca2+-independent PLA2 is suggested to play an important role in the release of linolenic acid, the precursor of jasmonic acid, through a signal transduction pathway.
Glucose and Disaccharide-Sensing Mechanisms Modulate the Expression of α-amylase in Barley Embryos
Authors: Loreti Elena , Alpi Amedeo , Perata Pierdomenico 
Published: July 2002

Abstract
The aim of this study was to investigate the sugar-sensing processes modulating the expression ofα-amylase in barley (Hordeum vulgaris L. var Himalaya) embryos. The results highlight the existence of independent glucose (Glc) and disaccharides sensing. Glc treatment destabilizes the α-amylase mRNA. Non-metabolizable disaccharides repress α-amylaseinduction, but have no effects on transcript stability. Structure-function analysis indicates that a fructose (Fru) moiety is needed for disaccharide sensing. Lactulose (β-galactose [Gal][1→4]Fru), palatinose (Glc[1→6]Fru), and turanose (Glc[1→3]Fru) are not metabolized but repressα-amylase. Disrupting the fructosyl moiety of lactulose and palatinose, or replacing the Fru moiety of β-Gal[1→4]Fru with Glc or Gal results in molecules unable to repress α-amylase. Comparison of the molecular requirements for sucrose transport with those for disaccharide sensing suggests that these sugars are perceived possibly at the plasma membrane level independently from sucrose transport.
Photodamage of the Photosynthetic Apparatus and Its Dependence on the Leaf Developmental Stage in the npq1 Arabidopsis Mutant Deficient in the Xanthophyll Cycle Enzyme Violaxanthin De-epoxidase
Authors: Havaux Michel , Bonfils Jean-Paul , Lütz Cornelius , Niyogi Krishna K. 
Published: July 2002

Abstract
The npq1 Arabidopsis mutant is deficient in the violaxanthin de-epoxidase enzyme that converts violaxanthin to zeaxanthin in excess light (xanthophyll cycle). We have compared the behavior of mature leaves (ML) and developing leaves of the mutant and the wild type in various light environments. Thermoluminescence measurements indicated that high photon flux densities (&gt;500 μmol m−2 s−1) promoted oxidative stress in the chloroplasts of npq1 ML, which was associated with a loss of chlorophyll and an inhibition of the photochemical activity. Illuminating leaf discs in the presence of eosin, a generator of singlet oxygen, brought about pronounced lipid peroxidation innpq1 ML but not in wild-type leaves. No such effects were seen in young leaves (YL) of npq1, which were quite tolerant to strong light and eosin-induced singlet oxygen. Non-photochemical energy quenching was strongly inhibited innpq1 YL and ML and was not improved with high-light acclimation. Our results confirm that the xanthophyll cycle protects chloroplasts from photooxidation by a mechanism distinct from non-photochemical energy quenching and they reveal that the absence of xanthophyll cycle can be compensated by other protective mechanisms.npq1 YL were observed to accumulate considerable amounts of vitamin E during photoacclimation, suggesting that this lipophilic antioxidant could be involved in the high phototolerance of those leaves.
Differential Subcellular Localization and Expression of ATP Sulfurylase and 5′-Adenylylsulfate Reductase during Ontogenesis of Arabidopsis Leaves Indicates That Cytosolic and Plastid Forms of ATP Sulfurylase May Have Specialized Functions
Authors: Rotte Carmen , Leustek Thomas 
Published: July 2002

Abstract
ATP sulfurylase and 5′-adenylylsulfate (APS) reductase catalyze two reactions in the sulfate assimilation pathway. Cell fractionation of Arabidopsis leaves revealed that ATP sulfurylase isoenzymes exist in the chloroplast and the cytosol, whereas APS reductase is localized exclusively in chloroplasts. During development of Arabidopsis plants the total activity of ATP sulfurylase and APS reductase declines by 3-fold in leaves. The decline in APS reductase can be attributed to a reduction of enzyme during aging of individual leaves, the highest activity occurring in the youngest leaves and the lowest in fully expanded leaves. By contrast, total ATP sulfurylase activity declines proportionally in all the leaves. The distinct behavior of ATP sulfurylase can be attributed to reciprocal expression of the chloroplast and cytosolic isoenzymes. The chloroplast form, representing the more abundant isoenzyme, declines in parallel with APS reductase during aging; however, the cytosolic form increases over the same period. In total, the results suggest that cytosolic ATP sulfurylase plays a specialized function that is probably unrelated to sulfate reduction. A plausible function could be in generating APS for sulfation reactions.
Oxygen Regulation of a Nodule-Located Carbonic Anhydrase in Alfalfa
Authors: Gálvez Susana , Hirsch Ann M. , Wycoff Keith L. , Hunt Stephen , Layzell David B. , Kondorosi Adam , Crespi Martin 
Published: July 2002

Abstract
Control of the permeability to oxygen is critical for the function of symbiotic nitrogen fixation in legume nodules. The inner cortex (IC) seems to be a primary site for this regulation. In alfalfa (Medicago sativa) nodules, expression of theMsca1 gene encoding a carbonic anhydrase (CA) was previously found to be restricted to the IC. We have now raised antibodies against recombinant Msca1 protein and used them, together with antibodies raised against potato leaf CA, to demonstrate the presence of two forms of CA in mature nodules. Each antibody recognizes a different CA isoform in nodule tissues. Immunolocalization revealed that leaf-related CAs were localized primarily in the nitrogen-fixing zone, whereas the Msca1protein was restricted exclusively to the IC region, in indeterminate and determinate nodules. In alfalfa nodules grown at various O2 concentrations, an inverse correlation was observed between the external oxygen pressure and Msca1 protein content in the IC, the site of the putative diffusion barrier. ThusMsca1 is a molecular target of physiological processes occurring in the IC cells involved in gas exchange in the nodule.
Microarray Analysis of Developing Arabidopsis Seeds
Authors: Girke Thomas , Todd Jim , Ruuska Sari , White Joe , Benning Christoph , Ohlrogge John 
Published: July 2002

Abstract
To provide a broad analysis of gene expression in developing Arabidopsis seeds, microarrays have been produced that display approximately 2,600 seed-expressed genes. DNA for genes spotted on the arrays were selected from &gt;10,000 clones partially sequenced from a cDNA library of developing seeds. Based on a series of controls, sensitivity of the arrays was estimated at one to two copies of mRNA per cell and cross hybridization was estimated to occur if closely related genes have &gt;70% to 80% sequence identity. These arrays have been hybridized in a series of experiments with probes derived from seeds, leaves, and roots of Arabidopsis. Analysis of expression ratios between the different tissues has allowed the tissue-specific expression patterns of many hundreds of genes to be described for the first time. Approximately 25% of the 2,600 genes were expressed at ratios ≥ 2-fold higher in seeds than leaves or roots and 10% at ratios ≥ 10. Included in this list are a large number of proteins of unknown function, and potential regulatory factors such as protein kinases, phosphatases, and transcription factors. The Arabidopsis arrays were also found to be useful for transcriptional profiling of mRNA isolated from developing oilseed rape (Brassica napus) seeds and expression patterns correlated well between the two species.
Arabidopsis RopGAPs Are a Novel Family of Rho GTPase-Activating Proteins that Require the Cdc42/Rac-Interactive Binding Motif for Rop-Specific GTPase Stimulation
Authors: Wu Guang , Li Hai , Yang Zhenbiao 
Published: July 2002

Abstract
The plant-specific Rop subfamily of Rho GTPases, most closely related to the mammalian Cdc42 and Rac GTPases, plays an important role in the regulation of calcium-dependent pollen tube growth, H2O2-mediated cell death, and many other processes in plants. In a search for Rop interactors using the two-hybrid method, we identified a family of Rho GTPase-activating proteins (GAP) from Arabidopsis, termed RopGAPs. In addition to a GAP catalytic domain, RopGAPs contain a Cdc42/Rac-interactive binding (CRIB) motif known to allow Cdc42/Rac effector proteins to bind activated Cdc42/Rac. This novel combination of a GAP domain with a CRIB motif is widespread in higher plants and is unique to the regulation of the Rop GTPase. A critical role for CRIB in the regulation of in vitro RopGAP activity was demonstrated using point and deletion mutations. Both types of mutants have drastically reduced capacities to stimulate the intrinsic Rop GTPase activity and to bind Rop. Furthermore, RopGAPs preferentially stimulate the GTPase activity of Rop, but not Cdc42 in a CRIB-dependent manner. In vitro binding assays show that the RopGAP CRIB domain interacts with GTP- and GDP-bound forms of Rop, as well as the transitional state of Rop mimicked by aluminum fluoride. The CRIB domain also promotes the association of the GAP domain with the GDP-bound Rop, as does aluminum fluoride. These results reveal a novel CRIB-dependent mechanism for the regulation of the plant-specific family of Rho GAPs. We propose that the CRIB domain facilitates the formation of or enhanced GAP-mediated stabilization of the transitional state of the Rop GTPase.
The ACA4 Gene of Arabidopsis Encodes a Vacuolar Membrane Calcium Pump That Improves Salt Tolerance in Yeast
Authors: Geisler Markus , Frangne Nathalie , Gomès Eric , Martinoia Enrico , Palmgren Michael G. 
Published: July 2002

Abstract
Several lines of evidence suggest that regulation of intracellular Ca2+ levels is crucial for adaptation of plants to environmental stress. We have cloned and characterized Arabidopsis auto-inhibited Ca2+-ATPase, isoform 4 (ACA4), a calmodulin-regulated Ca2+-ATPase. Confocal laser scanning data of a green fluorescent protein-tagged version of ACA4 as well as western-blot analysis of microsomal fractions obtained from two-phase partitioning and Suc density gradient centrifugation suggest that ACA4 is localized to small vacuoles. The N terminus of ACA4 contains an auto-inhibitory domain with a binding site for calmodulin as demonstrated through calmodulin-binding studies and complementation experiments using the calcium transport yeast mutant K616. ACA4 and PMC1, the yeast vacuolar Ca2+-ATPase, conferred protection against osmotic stress such as high NaCl, KCl, and mannitol when expressed in the K616 strain. An N-terminally modified form of ACA4 specifically conferred increased NaCl tolerance, whereas full-length ATPase had less effect.
Evidence for Symplastic Phloem Unloading in Sink Leaves of Barley
Authors: Haupt Sophie , Duncan George H. , Holzberg Steve , Oparka Karl J. 
Published: July 2002

Abstract
The pathway of phloem unloading in sink barley (Hordeum vulgare) leaves was studied using a combination of electron microscopy, carboxyfluorescein transport, and systemic movement of barley stripe mosaic virus expressing the green fluorescent protein. Studies of plasmodesmatal frequencies between the phloem and mesophyll indicated a symplastic sieve element- (SE) unloading pathway involving thick-walled and thin-walled SEs. Phloem-translocated carboxyfluorescein was unloaded rapidly from major longitudinal veins and entered the mesophyll cells of sink leaves. Unloading was “patchy” along the length of a vein, indicating that sieve element unloading may be discontinuous along a single vascular bundle. This pattern was mirrored precisely by the unloading of barley stripe mosaic virus expressing the green fluorescent protein. Transverse veins were not utilized in the unloading process. The data collectively indicate a symplastic mechanism of SE unloading in the sink barley leaf.
A Role for Brassinosteroids in Germination in Arabidopsis
Authors: Steber Camille M. , McCourt Peter 
Published: July 2002

Abstract
This paper presents evidence that plant brassinosteroid (BR) hormones play a role in promoting germination. It has long been recognized that seed dormancy and germination are regulated by the plant hormones abscisic acid (ABA) and gibberellin (GA). These two hormones act antagonistically with each other. ABA induces seed dormancy in maturing embryos and inhibits germination of seeds. GA breaks seed dormancy and promotes germination. Severe mutations in GA biosynthetic genes in Arabidopsis, such as ga1-3, result in a requirement for GA application to germinate. Whereas previous work has shown that BRs play a critical role in controlling cell elongation, cell division, and skotomorphogenesis, no germination phenotypes have been reported in BR mutants. We show that BR rescues the germination phenotype of severe GA biosynthetic mutants and of the GA-insensitive mutant sleepy1. This result shows that BR stimulates germination and raises the possibility that BR is needed for normal germination. If true, we would expect to detect a germination phenotype in BR mutants. We found that BR mutants exhibit a germination phenotype in the presence of ABA. Germination of both the BR biosynthetic mutantdet2-1 and the BR-insensitive mutantbri1-1 is more strongly inhibited by ABA than is germination of wild type. Thus, the BR signal is needed to overcome inhibition of germination by ABA. Taken together, these results point to a role for BRs in stimulating germination.
Regulation of Protein Degradation and Protease Expression by Mannose in Maize Root Tips. Pi Sequestration by Mannose May Hinder the Study of Its Signaling Properties
Authors: Brouquisse Renaud , Evrard Adeline , Rolin Dominique , Raymond Philippe , Roby Claude 
Published: July 2002

Abstract
The effects of mannose (Man) and glucose (Glc) on central metabolism, proteolysis, and expression of the root starvation-induced protease (RSIP; F. James, R. Brouquisse, C. Suire, A. Pradet, P. Raymond [1996] Biochem J 320: 283–292) were investigated in maize (Zea mays L. cv DEA) root tips. Changes in metabolite concentrations (sugars, ester-phosphates, adenine nucleotides, and amino acids) were monitored using in vivo and in vitro 13C- and 31P-NMR spectroscopy, in parallel with the changes in respiration rates, protein contents, proteolytic activities, and RSIP amounts. The inhibition of proteolysis, the decrease in proteolytic activities, and the repression of RSIP expression triggered by Man, at concentrations usually used to study sugar signaling (2 and 10 mm), were found to be related to a drop of energy metabolism, primarily due to a Man-induced Pi sequestration. However, when supplied at low concentration (2 mm) and with the adequate phosphate concentration (30 mm), energy metabolism was restored and Man repressed proteolysis similarly to Glc, when provided at the same concentration. These results indicate that Man should be used with caution as a Glc analog to study signalization by sugars in plants because possible signaling effects may be hindered by Pi sequestration.