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Rodney Croteau - One of the best experts on this subject based on the ideXlab platform.
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Strategies for transgenic manipulation of Monoterpene biosynthesis in plants.
2002Co-Authors: Soheil S. Mahmoud, Rodney CroteauAbstract:Monoterpenes, the C(10) isoprenoids, are a large family of natural products that are best known as constituents of the essential oils and defensive oleoresins of aromatic plants. In addition to ecological roles in pollinator attraction, allelopathy and plant defense, Monoterpenes are used extensively in the food, cosmetic and pharmaceutical industries. The importance of these plant products has prompted the definition of many Monoterpene biosynthetic pathways, the cloning of the relevant genes and the development of genetic transformation techniques for agronomically significant Monoterpene-producing plants. Metabolic engineering of Monoterpene biosynthesis in the model plant peppermint has resulted in yield increase and compositional improvement of the essential oil, and also provided strategies for manipulating flavor and fragrance production, and plant defense.
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regulation of Monoterpene accumulation in leaves of peppermint
2000Co-Authors: Jonathan Gershenzon, Marie E Mcconkey, Rodney CroteauAbstract:Plants 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 by 14 CO 2 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.
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floral scent production in clarkia onagraceae i localization and developmental modulation of Monoterpene emission and linalool synthase activity
1994Co-Authors: Eran Pichersky, Robert A Raguso, Efraim Lewinsohn, Rodney CroteauAbstract:The flowers of many plants emit volatile compounds as a means of attracting pollinators. We have previously shown that the strong, sweet fragrance of Clarkia breweri (Onagraceae), an annual plant native to California, consists of approximately 8 to 12 volatile compounds[mdash]three Monoterpenes and nine benzoate derivatives (R.A. Raguso and E. Pichersky [1994] Plant Syst Evol [in press]). Here we report that the Monoterpene alcohol linalool is synthesized and emitted mostly by petals but to a lesser extent also by the pistil and stamens. Two linalool oxides are produced and emitted almost exclusively by the pistil. These three Monoterpenes are first discernible in mature unopened buds, and their tissue levels are highest during the first 2 to 3 d after anthesis. Levels of emission by the different floral parts throughout the life span of the flower were correlated with levels of these Monoterpenes in the respective tissues, suggesting that these Monoterpenes are emitted soon after their synthesis. Activity of linalool synthase, an enzyme that converts the ubiquitous C10 isoprenoid intermediate geranyl pyrophosphate to linalool, was highest in petals, the organ that emits most of the linalool. However, linalool synthase activity on a fresh weight basis was highest in stigma and style (i.e. the pistil). Most of the linalool produced in the pistil is apparently converted into linalool oxides. Lower levels (0.1%) of Monoterpene emission and linalool synthase activity are found in the stigma of Clarkia concinna, a nonscented relative of C. breweri, suggesting that Monoterpenes may have other functions in the flower in addition to attracting pollinators.
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comparison of two Monoterpene cyclases isolated from higher plants γ terpinene synthase from thymus vulgaris and limonene synthase from mentha x piperita
1992Co-Authors: W R Alonso, Rodney CroteauAbstract:Monoterpenes are the C10 members of the terpenoid family of natural products, and they diverge from higher isoprenoid biosynthesis at the level of geranyl pyrophosphate. γ-Terpinene synthase and limonene synthase catalyze the divalent metal ion-dependent cyclization of geranyl pyrophosphate to cyclic Monoterpenes of the p-menthane type; however, γ-terpinene synthase generates a diverse assortment of minor Monoterpene co-products from geranyl pyrophosphate whereas limonene synthase produces a single product. The basic physical and chemical characteristics of these two Monoterpene cyclases are described and compared to properties of other terpene cyclases.
Joerg Bohlmann - One of the best experts on this subject based on the ideXlab platform.
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toxicity of pine Monoterpenes to mountain pine beetle
2017Co-Authors: Christine C Chiu, Christopher I Keeling, Joerg BohlmannAbstract:The mountain pine beetle (Dendroctonus ponderosae; MPB) is an eruptive bark beetle species affecting pine forests of western North America. MPB are exposed to volatile Monoterpenes, which are important host defense chemicals. We assessed the toxicity of the ten most abundant Monoterpenes of lodgepole pine (Pinus contorta), a major host in the current MPB epidemic, against adult MPB from two locations in British Columbia, Canada. Monoterpenes were tested as individual volatiles and included (−)-β-phellandrene, (+)-3-carene, myrcene, terpinolene, and both enantiomers of α-pinene, β-pinene and limonene. Dose-mortality experiments identified (−)-limonene as the most toxic (LC50: 32 μL/L), and (−)-α-pinene (LC50: 290 μL/L) and terpinolene (LC50: >500 μL/L) as the least toxic. MPB body weight had a significant positive effect on the ability to survive most Monoterpene volatiles, while sex did not have a significant effect with most Monoterpenes. This study helps to quantitatively define the effects of individual Monoterpenes towards MPB mortality, which is critical when assessing the variable Monoterpene chemical defense profiles of its host species.
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gene discovery for enzymes involved in limonene modification or utilization by the mountain pine beetle associated pathogen grosmannia clavigera
2014Co-Authors: Ye Wang, Joerg Bohlmann, Lina Madilao, Colette BreuilAbstract:To successfully colonize and eventually kill pine trees, Grosmannia clavigera (Gs cryptic species), the main fungal pathogen associated with the mountain pine beetle (Dendroctonus ponderosae), has developed multiple mechanisms to overcome host tree chemical defenses, of which terpenoids are a major component. In addition to a Monoterpene efflux system mediated by a recently discovered ABC transporter, Gs has genes that are highly induced by Monoterpenes and that encode enzymes that modify or utilize Monoterpenes [especially (+)-limonene]. We showed that pine-inhabiting Ophiostomale fungi are tolerant to Monoterpenes, but only a few, including Gs, are known to utilize Monoterpenes as a carbon source. Gas chromatography-mass spectrometry (GC-MS) revealed that Gs can modify (+)-limonene through various oxygenation pathways, producing carvone, p-mentha-2,8-dienol, perillyl alcohol, and isopiperitenol. It can also degrade (+)-limonene through the C-1-oxygenated pathway, producing limonene-1,2-diol as the most abundant intermediate. Transcriptome sequencing (RNA-seq) data indicated that Gs may utilize limonene 1,2-diol through beta-oxidation and then valine and tricarboxylic acid (TCA) metabolic pathways. The data also suggested that at least two gene clusters, located in genome contigs 108 and 161, were highly induced by Monoterpenes and may be involved in Monoterpene degradation processes. Further, gene knockouts indicated that limonene degradation required two distinct Baeyer-Villiger monooxygenases (BVMOs), an epoxide hydrolase and an enoyl coenzyme A (enoyl-CoA) hydratase. Our work provides information on enzyme-mediated limonene utilization or modification and a more comprehensive understanding of the interaction between an economically important fungal pathogen and its host's defense chemicals.
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Low-density Ceratocystis polonica inoculation of Norway spruce (Picea abies) triggers accumulation of Monoterpenes with antifungal properties
2014Co-Authors: Metka Novak, Joerg Bohlmann, Andreja Urbanek Krajnc, Ljerka Lah, Neja Zupanec, Nada Kraševec, Mitja Križman, Radovan KomelAbstract:Among the most devastating pests of Norway spruce ( Picea abies ) are the European spruce bark beetle ( Ips typographus ) and the associated pathogenic blue-stain fungus Ceratocystis polonica. Following attack and colonization, the beetle and the fungus must cope with induced host chemical defenses, such as Monoterpenes that are generally thought to be toxic to both symbionts. The goal of this study was to better understand the response of Norway spruce following C. polonica inoculation at low density that does not overwhelm the tree and to identify Monoterpenes mobilized toward the fungus. We inoculated healthy mature trees and monitored Monoterpene profiles 2, 3, and 5 months post-inoculation. We also exposed three different C. polonica strains to the most abundant or significantly up-regulated Monoterpenes to determine differences in Monoterpene toxicity and resistance among strains. Total Monoterpene levels, including limonene, were increased at 2 and 3 months after inoculation and had dropped after 5 months. In in vitro assays, all Monoterpenes were inhibitory to C. polonica . Limonene and β-pinene were the most potent inhibitors of fungal growth. The extent of inhibition varied between the three strains tested. These results showed a defense response of Norway spruce to C. polonica , in which limonene may play a critical role in inhibiting the spread of the fungus. We also showed that differences between strains of C. polonica must be taken into account when assessing the role of the fungus in this bark beetle–symbiont system.
Jens Harder - One of the best experts on this subject based on the ideXlab platform.
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Anaerobic Degradation of Bicyclic Monoterpenes in Castellaniella defragrans
2018Co-Authors: Edinson Puentes-cala, Stephanie Markert, Manuel Liebeke, Jens HarderAbstract:The microbial degradation pathways of bicyclic Monoterpenes contain unknown enzymes for carbon–carbon cleavages. Such enzymes may also be present in the betaproteobacterium Castellaniella defragrans, a model organism to study the anaerobic Monoterpene degradation. In this study, a deletion mutant strain missing the first enzyme of the monocyclic Monoterpene pathway transformed cometabolically the bicyclics sabinene, 3-carene and α-pinene into several monocyclic Monoterpenes and traces of cyclic Monoterpene alcohols. Proteomes of cells grown on bicyclic Monoterpenes resembled the proteomes of cells grown on monocyclic Monoterpenes. Many transposon mutants unable to grow on bicyclic Monoterpenes contained inactivated genes of the monocyclic Monoterpene pathway. These observations suggest that the monocyclic degradation pathway is used to metabolize bicyclic Monoterpenes. The initial step in the degradation is a decyclization (ring-opening) reaction yielding monocyclic Monoterpenes, which can be considered as a reverse reaction of the olefin cyclization of polyenes
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microbial Monoterpene transformations a review
2014Co-Authors: Robert Marmulla, Jens HarderAbstract:Isoprene and Monoterpenes constitute a significant fraction of new plant biomass. Emission rates into the atmosphere alone are estimated to be over 500 Tg per year. These natural hydrocarbons are mineralized annually in similar quantities. In the atmosphere, abiotic photochemical processes cause lifetimes of minutes to hours. Microorganisms encounter isoprene, Monoterpenes and other volatiles of plant origin while living in and on plants, in the soil and in aquatic habitats. Below toxic concentrations, the compounds can serve as carbon and energy source for aerobic and anaerobic microorganisms. Besides these catabolic reactions, transformations may occur as part of detoxification processes. Initial transformations of Monoterpenes involve the introduction of functional groups, oxidation reactions and molecular rearrangements catalyzed by various enzymes. Pseudomonas and Rhodococcus strains and members of the genera Castellaniella and Thauera have become model organisms for the elucidation of biochemical pathways. We review here the enzymes and their genes together with microorganisms known for a Monoterpene metabolism, with a strong focus on microorganisms that are taxonomically validly described and currently available from culture collections. Metagenomes of microbiomes with a Monoterpene-rich diet confirmed the ecological relevance of Monoterpene metabolism and raised concerns on the quality of our insights based on the limited biochemical knowledge.
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The oxygen-independent metabolism of cyclic Monoterpenes in Castellaniella defragrans 65Phen.
2014Co-Authors: Jan Petasch, Eva-maria Disch, Stephanie Markert, Dörte Becher, Thomas Schweder, Bruno Hüttel, Richard Reinhardt, Jens HarderAbstract:Background: The facultatively anaerobic betaproteobacterium Castellaniella defragrans 65Phen utilizes acyclic, monocyclic and bicyclic Monoterpenes as sole carbon source under oxic as well as anoxic conditions. A biotransformation pathway of the acyclic β-myrcene required linalool dehydratase-isomerase as initial enzyme acting on the hydrocarbon. An in-frame deletion mutant did not use myrcene, but was able to grow on monocyclic Monoterpenes. The genome sequence and a comparative proteome analysis together with a random transposon mutagenesis were conducted to identify genes involved in the monocyclic Monoterpene metabolism. Metabolites accumulating in cultures of transposon and in-frame deletion mutants disclosed the degradation pathway. Results: Castellaniella defragrans 65Phen oxidizes the monocyclic Monoterpene limonene at the primary methyl group forming perillyl alcohol. The genome of 3.95 Mb contained a 70 kb genome island coding for over 50 proteins involved in the Monoterpene metabolism. This island showed higher homology to genes of another Monoterpene-mineralizing betaproteobacterium, Thauera terpenica 58Eu T , than to genomes of the family Alcaligenaceae, which harbors the genus Castellaniella. A collection of 72 transposon mutants unable to grow on limonene contained 17 inactivated genes, with 46 mutants located in the two genes ctmAB (cyclic terpene metabolism). CtmA and ctmB were annotated as FAD-dependent oxidoreductases and clustered together with ctmE, a 2Fe-2S ferredoxin gene, and ctmF, coding for a NADH:ferredoxin oxidoreductase. Transposon mutants of ctmA, B or E did not grow aerobically or anaerobically on limonene, but on perillyl alcohol. The next steps in the pathway are catalyzed by the geraniol dehydrogenase GeoA and the geranial dehydrogenase GeoB, yielding perillic acid. Two transposon mutants had inactivated genes of the Monoterpene ring cleavage (mrc) pathway. 2-Methylcitrate synthase and 2-methylcitrate dehydratase were also essential for the Monoterpene metabolism but not for growth on acetate. Conclusions: The genome of Castellaniella defragrans 65Phen is related to other genomes of Alcaligenaceae ,b ut contains a genomic island with genes of the Monoterpene metabolism. Castellaniella defragrans 65Phen degrades limonene via a limonene dehydrogenase and the oxidation of perillyl alcohol. The initial oxidation at the primary methyl group is independent of molecular oxygen.
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the oxygen independent metabolism of cyclic Monoterpenes in castellaniella defragrans 65phen
2014Co-Authors: Jan Petasch, Eva-maria Disch, Stephanie Markert, Dörte Becher, Thomas Schweder, Bruno Hüttel, Richard Reinhardt, Jens HarderAbstract:The facultatively anaerobic betaproteobacterium Castellaniella defragrans 65Phen utilizes acyclic, monocyclic and bicyclic Monoterpenes as sole carbon source under oxic as well as anoxic conditions. A biotransformation pathway of the acyclic β-myrcene required linalool dehydratase-isomerase as initial enzyme acting on the hydrocarbon. An in-frame deletion mutant did not use myrcene, but was able to grow on monocyclic Monoterpenes. The genome sequence and a comparative proteome analysis together with a random transposon mutagenesis were conducted to identify genes involved in the monocyclic Monoterpene metabolism. Metabolites accumulating in cultures of transposon and in-frame deletion mutants disclosed the degradation pathway. Castellaniella defragrans 65Phen oxidizes the monocyclic Monoterpene limonene at the primary methyl group forming perillyl alcohol. The genome of 3.95 Mb contained a 70 kb genome island coding for over 50 proteins involved in the Monoterpene metabolism. This island showed higher homology to genes of another Monoterpene-mineralizing betaproteobacterium, Thauera terpenica 58EuT, than to genomes of the family Alcaligenaceae, which harbors the genus Castellaniella. A collection of 72 transposon mutants unable to grow on limonene contained 17 inactivated genes, with 46 mutants located in the two genes ctmAB (cyclic terpene metabolism). CtmA and ctmB were annotated as FAD-dependent oxidoreductases and clustered together with ctmE, a 2Fe-2S ferredoxin gene, and ctmF, coding for a NADH:ferredoxin oxidoreductase. Transposon mutants of ctmA, B or E did not grow aerobically or anaerobically on limonene, but on perillyl alcohol. The next steps in the pathway are catalyzed by the geraniol dehydrogenase GeoA and the geranial dehydrogenase GeoB, yielding perillic acid. Two transposon mutants had inactivated genes of the Monoterpene ring cleavage (mrc) pathway. 2-Methylcitrate synthase and 2-methylcitrate dehydratase were also essential for the Monoterpene metabolism but not for growth on acetate. The genome of Castellaniella defragrans 65Phen is related to other genomes of Alcaligenaceae, but contains a genomic island with genes of the Monoterpene metabolism. Castellaniella defragrans 65Phen degrades limonene via a limonene dehydrogenase and the oxidation of perillyl alcohol. The initial oxidation at the primary methyl group is independent of molecular oxygen.
Gary J. Blomquist - One of the best experts on this subject based on the ideXlab platform.
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Unique animal prenyltransferase with Monoterpene synthase activity.
2009Co-Authors: Albert B. Gilg, Claus Tittiger, Gary J. BlomquistAbstract:Monoterpenes are structurally diverse natural compounds that play an essential role in the chemical ecology of a wide array of organisms. A key enzyme in Monoterpene biosynthesis is geranyl diphosphate synthase (GPPS). GPPS is an isoprenyl diphosphate synthase that catalyzes a single electrophilic condensation reaction between dimethylallyl diphosphate (C5) and isopentenyl diphosphate (C5) to produce geranyl diphosphate (GDP; C10). GDP is the universal precursor to all Monoterpenes. Subsequently, Monoterpene synthases are responsible for the transformation of GDP to a variety of acyclic, monocyclic, and bicyclic Monoterpene products. In pheromone-producing male Ips pini bark beetles (Coleoptera: Scolytidae), the acyclic Monoterpene myrcene is required for the production of the major aggregation pheromone component, ipsdienol. Here, we report Monoterpene synthase activity associated with GPPS of I. pini. Enzyme assays were performed on recombinant GPPS to determine the presence of Monoterpene synthase activity, and the reaction products were analyzed by coupled gas chromatography–mass spectrometry. The functionally expressed recombinant enzyme produced both GDP and myrcene, making GPPS of I. pini a bifunctional enzyme. This unique insect isoprenyl diphosphate synthase possesses the functional plasticity that is characteristic of terpene biosynthetic enzymes of plants, contributing toward the current understanding of product specificity of the isoprenoid pathway.
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isolation and functional expression of an animal geranyl diphosphate synthase and its role in bark beetle pheromone biosynthesis
2005Co-Authors: Albert B. Gilg, Claus Tittiger, Jeremy C Bearfield, William Welch, Gary J. BlomquistAbstract:Geranyl diphosphate synthase (GPPS) catalyzes the condensation of dimethylallyl diphosphate and isopentenyl diphosphate to form geranyl diphosphate. Geranyl diphosphate is the precursor of Monoterpenes, a large family of natural occurring C10 compounds predominately found in plants. Similar to plants but unique to animals, some bark beetle genera (Coleoptera: Scolytidae) produce Monoterpenes that function in intraspecific chemical communication as aggregation and dispersion pheromones. The release of Monoterpene aggregation pheromone mediates host colonization and mating. It has been debated whether these Monoterpene pheromone components are derived de novo through the mevalonate pathway or result from simple modifications of dietary precursors. The data reported here provide conclusive evidence for de novo biosynthesis of Monoterpene pheromone components from bark beetles. We describe GPPS in the midgut tissue of pheromone-producing male Ips pini. GPPS expression levels are regulated by juvenile hormone III, similar to other mevalonate pathway genes involved in pheromone biosynthesis. In addition, GPPS transcript is almost exclusively expressed in the anterior midgut of male I. pini, the site of aggregation pheromone biosynthesis. The recombinant enzyme was functionally expressed and produced geranyl diphosphate as its major product. The three-dimensional model structure of GPPS shows that the insect enzyme has the sequence structural motifs common to E-isoprenyl diphosphate synthases.
Francesco Loreto - One of the best experts on this subject based on the ideXlab platform.
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Impact of ozone on Monoterpene emissions and evidence for an isoprene-like antioxidant action of Monoterpenes emitted by Quercus ilex leaves.
2004Co-Authors: Francesco Loreto, Paola Pinelli, Fausto Manes, Hannes KollistAbstract:Quercus ilex (L.) leaves emit Monoterpenes, particularly alpha-pinene, beta-pinene and sabinene. Apart from the Monoterpene pools that are stored in specialized structures and have a clear defensive or attractive role, the function of Monoterpenes in Q. ilex leaves is unknown. We tested whether Monoterpenes have an antioxidant role, as has previously been found for isoprene in isoprene-emitting leaves. We exposed Q. ilex leaves to either mild and repeated ozone exposure (Experiment I) or to a single acute ozone exposure (Experiment II) at temperatures ranging between 20 and 32 degrees C. Both ozone treatments rapidly stimulated Monoterpene synthesis, but had no effect on photosynthesis and caused no visible damage to leaves maintained at 25, 30 or 32 degrees C. Ozone inhibited both photosynthesis and Monoterpene synthesis in leaves maintained at 20 degrees C. To characterize the relationship between Monoterpenes and ozone-induced damage, we fed detached leaves fosmidomycin, a selective inhibitor of isoprene synthesis. Fosmidomycin caused rapid and complete inhibition of Monoterpene emissions in leaves maintained at 30 degrees C, confirming that Monoterpenes are synthesized by the same biochemical pathway as isoprene. However, over the experimental period, fosmidomycin did not affect concentrations of compounds that are formed from chloroplastic isoprenoids and that might have conferred antioxidant protection, either directly (carotenoids) or indirectly (chlorophylls, xanthophylls). In leaves whose Monoterpene synthesis had been inhibited by fosmidomycin, ozone rapidly and significantly inhibited photosynthesis and increased the production of hydrogen peroxide and malonyldialdehyde. We conclude that Monoterpenes produced by Q. ilex leaves share the same biosynthetic pathway and function as isoprene. Furthermore, all volatile isoprenoids may have similar antioxidant properties and may be stimulated by the same stress-inducing conditions.
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Monoterpene emission and Monoterpene synthase activities in the Mediterranean evergreen oak Quercus ilex L. grown at elevated CO2 concentrations
2001Co-Authors: Francesco Loreto, Jörg-peter Schnitzler, Paolo Ciccioli, Enzo Brancaleoni, Robert Fischbach, Carlo Calfapietra, Guenther SeufertAbstract:Monoterpene emissions, Monoterpene synthase activities, photosynthesis, fluorescence yield in the dark and drought stress indicators (stomatal conductance and mid-day water potential) were concurrently measured under similar temperature and illumination in current-year leaves of Quercus ilex L. of plants grown in open-top chambers at ambient (350 ppm) and elevated (700 ppm) CO2. The study was undertaken to understand the effect of CO2 on Monoterpene biosynthesis, and to predict and parameterize the biogenic emissions at growing CO2 concentrations. The results of the 1998 and 1999 studies show that at elevated CO2, and in the absence of persistent environmental stresses, photosynthesis was stimulated with respect to ambient CO2, but that the emission of the three most abundantly emitted Monoterpenes (a-pinene, sabinene and b-pinene) was inhibited by approximately 68%. The enzyme activities of the Monoterpene synthases catalysing the formation of the three Monoterpenes were also inhibited at elevated CO2 and an excellent relationship was found between Monoterpene emission and activity of the corresponding enzyme both at ambient and elevated CO2. Interestingly, however, limonene emission was enhanced in conditions of elevated CO2 as it was also the corresponding synthase. The ratio between enzyme activity and emission of the three main Monoterpenes was high (above 20) at ambient CO2 but it was below 10 at elevated CO2 and, for limonene, on both treatments. Our results indicate that the overall emission of Monoterpenes at elevated CO2 will be inhibited because of a concurrent, strong down-regulation of Monoterpene synthase activities. When the enzyme activity does not change, as for limonene, the high photosynthetic carbon availability at elevated CO2 conditions may even stimulate emission. The results of the 1997 study show that severe and persistent drought, as commonly occurs in the Mediterranean, may inhibit both photosynthesis and Monoterpene (a-pinene) emission, particularly at ambient CO2. Thus, emission is probably limited by photosynthetic carbon availability; the effect of elevated CO2 per se is not apparent if drought, and perhaps other environmental stresses, are also present.
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fumigation with exogenous Monoterpenes of a non isoprenoid emitting oak quercus suber Monoterpene acquisition translocation and effect on the photosynthetic properties at high temperatures
2000Co-Authors: Sebastiano Delfine, Guenther Seufert, Olav Csiky, Francesco LoretoAbstract:We tested if fumigation with exogenous Monoterpenes might induce thermotolerance in leaves of an oak species (Quercus suber) which does not form and emit isoprenoids. To understand if exogenous Monoterpene fumigation results in internal accumulation of Monoterpenes, a physical method of Monoterpene extraction was used. The internal content of Monoterpenes increased in concert with increasing fumigation doses. This unambiguously demonstrated acquisition of exogenous Monoterpenes. We exposed fumigated Q. suber leaves to two cycles of increasing temperatures from 35 to 55°C at 5°C steps. When leaves were exposed to a low dose of exogenous Monoterpenes, yielding an internal content similar to that endogenously formed in the leaves of the Monoterpene-emitter Q. ilex, no clear improvement in thermotolerance was found. When leaves were exposed to a high dose of exogenous Monoterpenes, yielding an internal content of about five fold the endogenous pool of Q. ilex, but comparable with the expected content following stress-induced stomatal closure, photosynthesis inhibition at high temperatures was attenuated. This effect was observed only at temperatures < 45°C during the first cycle, but at all temperatures between 35 and 55°C when plants were exposed to two cycles of high temperatures. Monoterpenes were still found in the leaves of Q. suber 12 h after ending the fumigation. Monoterpenes were also found in non-fumigated leaves distant up to 45 cm from the fumigated leaves. If Monoterpenes make the photosynthetic apparatus more resistant to high temperatures, the effect might not be limited to the fumigated leaves and might be persistent after fumigation.
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On the Monoterpene emission under heat stress and on the increased thermotolerance of leaves of Quercus ilex L. fumigated with selected Monoterpenes
1998Co-Authors: Francesco Loreto, A. Förster, M. Dürr, Olav Csiky, Guenther SeufertAbstract:Leaves of the Monoterpene emitter Quercus ilex were exposed to a temperature ramp with 5 °C steps from 30 to 55 °C while maintained under conditions in which endogenous emission of Monoterpenes was allowed or suppressed, or under fumigation with selected exogenous Monoterpenes. Fumigation with Monoterpenes reduced the decline of photosynthesis, photorespiration and Monoterpene emission found in non-fumigated leaves exposed to high temperatures. It also substantially increased respiration when photosynthesis and photorespiration were inhibited by low O2 and CO2-free air. These results indicate that, as previously reported for isoprene, Monoterpenes may help plants cope with heat stress. Monoterpenes may enhance membrane stability, thus providing a rather non-specific protection of photosynthetic and respiratory processes. Monoterpene emission was maximal at a temperature of 35 °C and was inhibited at higher temperatures. This is likely to be the result of the temperature dependency of the enzymes involved in Monoterpene synthesis. In contrast to other Monoterpenes, cis- and trans-β-ocimene did not respond to exposure to high temperatures. Cis-β-ocimene also did not respond to low O2 or to fumigation. These results indicate that cis and trans-β-ocimene may have a different pathway of formation that probably does not involve enzymatic synthesis.
