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Thomas D. Sharkey - One of the best experts on this subject based on the ideXlab platform.
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Isoprene synthase genes form a monophyletic clade of acyclic terpene synthases in the TPS-B terpene synthase family.
Evolution; international journal of organic evolution, 2012Co-Authors: Thomas D. Sharkey, Dennis W. Gray, Heather K. Pell, Steven R. Breneman, Lauren A. TopperAbstract:Many plants emit significant amounts of Isoprene, which is hypothesized to help leaves tolerate short episodes of high temperature. Isoprene emission is found in all major groups of land plants including mosses, ferns, gymnosperms, and angiosperms; however, within these groups Isoprene emission is variable. The patchy distribution of Isoprene emission implies an evolutionary pattern characterized by many origins or many losses. To better understand the evolution of Isoprene emission, we examine the phylogenetic relationships among Isoprene synthase and monoterpene synthase genes in the angiosperms. In this study we identify nine new Isoprene synthases within the rosid angiosperms. We also document the capacity of a myrcene synthase in Humulus lupulus to produce Isoprene. Isoprene synthases and (E)-β-ocimene synthases form a monophyletic group within the Tps-b clade of terpene synthases. No asterid genes fall within this clade. The chemistry of Isoprene synthase and ocimene synthase is similar and likely affects the apparent relationships among Tps-b enzymes. The chronology of rosid evolution suggests a Cretaceous origin followed by many losses of Isoprene synthase over the course of evolutionary history. The phylogenetic pattern of Tps-b genes indicates that Isoprene emission from non-rosid angiosperms likely arose independently.
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Isoprene Emission from Plants: Why and How
Annals of botany, 2007Co-Authors: Thomas D. Sharkey, Amy E. Wiberley, Autumn R. DonohueAbstract:BACKGROUND Some, but not all, plants emit Isoprene. Emission of the related monoterpenes is more universal among plants, but the amount of Isoprene emitted from plants dominates the biosphere-atmosphere hydrocarbon exchange. SCOPE The emission of Isoprene from plants affects atmospheric chemistry. Isoprene reacts very rapidly with hydroxyl radicals in the atmosphere making hydroperoxides that can enhance ozone formation. Aerosol formation in the atmosphere may also be influenced by biogenic Isoprene. Plants that emit Isoprene are better able to tolerate sunlight-induced rapid heating of leaves (heat flecks). They also tolerate ozone and other reactive oxygen species better than non-emitting plants. Expression of the Isoprene synthase gene can account for control of Isoprene emission capacity as leaves expand. The emission capacity of fully expanded leaves varies through the season but the biochemical control of capacity of mature leaves appears to be at several different points in Isoprene metabolism. CONCLUSIONS The capacity for Isoprene emission evolved many times in plants, probably as a mechanism for coping with heat flecks. It also confers tolerance of reactive oxygen species. It is an example of isoprenoids enhancing membrane function, although the mechanism is likely to be different from that of sterols. Understanding the regulation of Isoprene emission is advancing rapidly now that the pathway that provides the substrate is known.
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Evolution of the Isoprene Biosynthetic Pathway in Kudzu
Plant physiology, 2005Co-Authors: Thomas D. Sharkey, Amy E. Wiberley, Tanya G. Falbel, Sansun Yeh, Deming Gong, Donna E. FernandezAbstract:Isoprene synthase converts dimethylallyl diphosphate, derived from the methylerythritol 4-phosphate (MEP) pathway, to Isoprene. Isoprene is made by some plants in substantial amounts, which affects atmospheric chemistry, while other plants make no Isoprene. As part of our long-term study of Isoprene synthesis, the genetics of the Isoprene biosynthetic pathway of the Isoprene emitter, kudzu (Pueraria montana), was compared with similar genes in Arabidopsis (Arabidopsis thaliana), which does not make Isoprene. The MEP pathway genes in kudzu were similar to the corresponding Arabidopsis genes. Isoprene synthase genes of kudzu and aspen (Populus tremuloides) were cloned to compare their divergence with the divergence seen in MEP pathway genes. Phylogenetic analysis of the terpene synthase gene family indicated that Isoprene synthases are either within the monoterpene synthase clade or sister to it. In Arabidopsis, the gene most similar to Isoprene synthase is a myrcene/ocimene (acyclic monoterpenes) synthase. Two phenylalanine residues found exclusively in Isoprene synthases make the active site smaller than other terpene synthase enzymes, possibly conferring specificity for the five-carbon substrate rather than precursors of the larger isoprenoids. Expression of the kudzu Isoprene synthase gene in Arabidopsis caused Arabidopsis to emit Isoprene, indicating that whether or not a plant emits Isoprene depends on whether or not it has a terpene synthase capable of using dimethylallyl diphosphate.
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Development of the capacity for Isoprene emission in kudzu
Plant Cell and Environment, 2005Co-Authors: Amy E. Wiberley, Autumn R. Linskey, Tanya G. Falbel, Thomas D. SharkeyAbstract:Isoprene is a biogenic hydrocarbon that has significant effects on tropospheric chemistry. It is emitted by a number of plant species, including kudzu, a leguminous vine that grows profusely in the south-eastern United States. This study investigated development of the capacity for Isoprene emission in kudzu. Previous studies examined Isoprene emission during leaf development, but a molecular explanation for the observed developmental delay in emission was lacking. This study found that kudzu leaves grown at a high temperature could emit Isoprene at least a week before they were fully expanded and 1 d after becoming photosynthetically competent. When grown at low temperature, however, leaves did not emit Isoprene until 1 week after they became fully expanded and 2 weeks after the onset of photosynthetic competence. Levels of mRNA and protein for Isoprene synthase, which catalyses the final step in Isoprene biosynthesis, were investigated; it was found that transcription and translation of this gene began at the same developmental stage as onset of emission in both growth conditions. Therefore, plant growth conditions, not leaf developmental stage, have primary control over expression of Isoprene synthase and onset of kudzu Isoprene emission. This finding may be useful in modelling early season Isoprene emission rates.
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Rapid regulation of the methylerythritol 4-phosphate pathway during Isoprene synthesis
Plant Physiology, 2004Co-Authors: Michael Wolfertz, Thomas D. Sharkey, Wilhelm Boland, Frank KühnemannAbstract:More volatile organic carbon is lost from plants as Isoprene than any other molecule. This flux of carbon to the atmosphere affects atmospheric chemistry and can serve as a substrate for ozone production in polluted air. Isoprene synthesis may help leaves cope with heatflecks and active oxygen species. Isoprene synthase, an enzyme related to monoterpene synthases, converts dimethylallyl diphosphate derived from the methylerythritol 4-phosphate pathway to Isoprene. We used dideuterated deoxyxylulose (DOX-d2) to study the regulation of the Isoprene biosynthetic pathway. Exogenous DOX-d2 displaced endogenous sources of carbon for Isoprene synthesis without increasing the overall rate of Isoprene synthesis. However, at higher concentrations, DOX-d2 completely suppressed Isoprene synthesis from endogenous sources and increased the overall rate of Isoprene synthesis. We interpret these results to indicate strong feedback control of deoxyxylulose-5-phosphate synthase. We related the emission of labeled Isoprene to the concentration of labeled dimethylallyl diphosphate in order to estimate the in situ Km of Isoprene synthase. The results confirm that Isoprene synthase has a Km 10- to 100-fold higher for its allylic diphosphate substrate than related monoterpene synthases for geranyl diphosphate.
Frederic Bonfils - One of the best experts on this subject based on the ideXlab platform.
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study of chain branching in natural rubber using size exclusion chromatography coupled with a multi angle light scattering detector sec mals
European Polymer Journal, 2009Co-Authors: Chandy Kim, Jerome Sainte Beuve, Stephane Guilbert, Frederic BonfilsAbstract:Abstract The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly( cis -1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly( cis -1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains ( M w cis -1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 M w cis -1,4-Isoprene) and nanoaggregates with rather compact structures.
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study of chain branching in natural rubber using size exclusion chromatography coupled with a multi angle light scattering detector sec mals
European Polymer Journal, 2009Co-Authors: Chandy Kim, Jerome Sainte Beuve, Stephane Guilbert, Frederic BonfilsAbstract:The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly(cis-1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly(cis-1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains (Mw < 1000 kg/mol). Using a master curve of linear standard poly(- cis-1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 < Mw < 10,000 kg/mol) of natural rubber contrary to previous studies. This study showed that the soluble portion of NR samples was composed of almost linear poly(cis- 1,4-Isoprene) and nanoaggregates with rather compact structures. (Resume d'auteur)
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Study of chain branching in natural rubber using size-exclusion chromatography coupled with a multi-angle light scattering detector (SEC-MALS)
European Polymer Journal, 2009Co-Authors: Chandy Kim, Stephane Guilbert, Jérôme Sainte Beuve, Frederic BonfilsAbstract:The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly(cis-1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly(cis-1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains (M(w) < 1000 kg/mol). Using a master curve of linear standard poly(-cis-1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 < M(w) < 10,000 kg/mol) of natural rubber contrary to previous studies. This study showed that the soluble portion of NR samples was composed of almost linear poly(cis-1,4-Isoprene) and nanoaggregates with rather compact structures.
Chandy Kim - One of the best experts on this subject based on the ideXlab platform.
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study of chain branching in natural rubber using size exclusion chromatography coupled with a multi angle light scattering detector sec mals
European Polymer Journal, 2009Co-Authors: Chandy Kim, Jerome Sainte Beuve, Stephane Guilbert, Frederic BonfilsAbstract:Abstract The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly( cis -1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly( cis -1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains ( M w cis -1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 M w cis -1,4-Isoprene) and nanoaggregates with rather compact structures.
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study of chain branching in natural rubber using size exclusion chromatography coupled with a multi angle light scattering detector sec mals
European Polymer Journal, 2009Co-Authors: Chandy Kim, Jerome Sainte Beuve, Stephane Guilbert, Frederic BonfilsAbstract:The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly(cis-1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly(cis-1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains (Mw < 1000 kg/mol). Using a master curve of linear standard poly(- cis-1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 < Mw < 10,000 kg/mol) of natural rubber contrary to previous studies. This study showed that the soluble portion of NR samples was composed of almost linear poly(cis- 1,4-Isoprene) and nanoaggregates with rather compact structures. (Resume d'auteur)
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Study of chain branching in natural rubber using size-exclusion chromatography coupled with a multi-angle light scattering detector (SEC-MALS)
European Polymer Journal, 2009Co-Authors: Chandy Kim, Stephane Guilbert, Jérôme Sainte Beuve, Frederic BonfilsAbstract:The different rheological behaviour of natural rubber (NR) compared to industrial synthetic poly(cis-1,4-Isoprene) (SR) has been attributed to the gel phase and long-chain branching. Previous studies on branching in NR were carried out using the fractionation technique by precipitation to obtain narrow molar mass distribution. In this study, chain branching of poly(cis-1,4-Isoprene) in NR was characterised by size-exclusion chromatography coupled with an online multi-angle light scattering detector (SEC-MALS). The nanoaggregates adsorbed on the column packing interfered with branching characterisation for short and medium chains (M(w) < 1000 kg/mol). Using a master curve of linear standard poly(-cis-1,4-Isoprenes), SEC-MALS revealed no or very little branching in the higher chains (1000 < M(w) < 10,000 kg/mol) of natural rubber contrary to previous studies. This study showed that the soluble portion of NR samples was composed of almost linear poly(cis-1,4-Isoprene) and nanoaggregates with rather compact structures.
Ray Fall - One of the best experts on this subject based on the ideXlab platform.
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Final Technical Report: Microbial Production of Isoprene
2003Co-Authors: Ray FallAbstract:OAK B135 We have discovered that bacteria produce and emit the hydrocarbon Isoprene (2-methyl-1,3-butadiene), and have suggested that if Isoprene-producing enzymes and their genes can be harnessed, useful hydrocarbon-producing systems might be constructed. The main goal of the proposed work was to establish the biochemical mechanism and regulation of Isoprene formation in the model bacterial system, Bacillus subtilis. In this 3-year project we (a) characterized the physiological regulation of Isoprene formation in B. subtilis and its relationship to Isoprene formation in plant chloroplasts; (b) analyzed genetic controls on Isoprene formation in B. subtilis; and (c) developed models to explain the biochemical rationale for Isoprene formation. We are also pursued (d) new methods for continuous measurement of Isoprene release in bioreactors, and (e) determined the presence of Isoprene-forming Bacillus on plant roots and used B. subtilis as a biocontrol agent for protection of plant roots from plant pathogenic bacteria. We have made significant advances in several areas. These include: (1) establishing the enzymatic basis of Isoprene formation in B. subtilis, and demonstrating throughout growth in a bioreactor that Isoprene synthase activity rises and falls with each of three peaks of Isoprene release (i.e. it appears to be a regulated enzyme). (2)more » We have explored genetic aspects of Isoprene formation, using gene disruption methods to greatly alter the patterns of Isoprene formation in bioreactors. Analysis of these mutants and alteration of cellular levels of dimethylallyl diphosphate (DMAPP), the substrate for Isoprene synthase, has led to the formulation of two models to explain why Isoprene is formed: an isoprenoid overflow model and a signaling model. We have obtained compelling evidence that Isoprene releases in bioreactors result from metabolic overflow. However, we have yet to determine the pattern of Isoprene formation when these bacteria are grown in a more natural state (e.g. as biofilms on surfaces). (3) We successfully used on-line mass spectrometry methods to measure release of volatiles, including Isoprene, from bioreactors during growth of B. subtilis. This methodology, still in its infancy, may provide a new means to assess physiological processes during industrial growth of Bacillus species, and use Isoprene formation as a barometer of carbon flow in these bacteria. (4) We also addressed the question: is Bacillus Isoprene formation analogous to chloroplast processes? This research was initiated because of the continuing interest in the puzzle of Isoprene formation in leaf chloroplasts. In pursuit of linkages between bacterial and plant Isoprene formation, we used our DMAPP assay to demonstrate that leaves of the Isoprene-emitter (cottonwood) show a diurnal cycle, peaking at mid-day in parallel with Isoprene release. Thus it appears that in two different biological systems Isoprene formation is highly regulated, and linked to isoprenoid carbon availability. (5) We developed a new method to detect Bacillus species in plant root samples, and demonstrated that plant roots are a rich source of biofilm-forming B. subtilis. Furthermore, using cultured Arabidopsis roots as a test system, we were able to demonstrate the formation of stable, viable Bacillus biofilms on the roots. Such roots were protected from killing by a root pathogenic Pseudomonas syringae strain. We have now formulated a mechanism to explain how such biocontrol by B. subtilis occurs, and future work will explore the role of Isoprene in signaling between different rhizobacteria and plant roots.« less
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increased co2 uncouples growth from Isoprene emission in an agriforest ecosystem
Nature, 2003Co-Authors: Russell K Monson, Ray Fall, Todd N Rosenstiel, Mark Potosnak, Kevin L GriffinAbstract:The emission of Isoprene from the leaves of forest trees is a fundamental component of biosphere–atmosphere interactions, controlling many aspects of photochemistry in the lower atmosphere1,2,3. As almost all commercial agriforest species emit high levels of Isoprene4, proliferation of agriforest plantations has significant potential to increase regional ozone pollution5,6,7 and enhance the lifetime of methane8, an important determinant of global climate. Here we show that growth of an intact Populus deltoides plantation under increased CO2 (800 µmol mol-1 and 1,200 µmol mol-1) reduced ecosystem Isoprene production by 21% and 41%, while above-ground biomass accumulation was enhanced by 60% and 82%, respectively. Exposure to increased CO2 significantly reduced the cellular content of dimethylallyl diphosphate, the substrate for Isoprene synthesis, in both leaves and leaf protoplasts. We identify intracellular metabolic competition for phosphoenolpyruvate as a possible control point in explaining the suppression of Isoprene emission under increased CO2. Our results highlight the potential for uncoupling Isoprene emission from biomass accumulation in an agriforest species, and show that negative air-quality effects of proliferating agriforests may be offset by increases in CO2.
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Isoprene synthase activity parallels fluctuations of Isoprene release during growth of Bacillus subtilis.
Biochemical and biophysical research communications, 2002Co-Authors: Tami L Sivy, Megan C. Shirk, Ray FallAbstract:Isoprene is a volatile metabolite of uncertain function in plants, animals, and bacteria. Here, we demonstrate that the Isoprene-producing bacterium, Bacillus subtilis, contains an Isoprene synthase activity that catalyzes dimethylallyl diphosphate-dependent Isoprene formation. Although the enzyme was very labile, it was demonstrated in both permeabilized cells and in partially purified cell extracts. Its activity was optimal at pH 6.2, required low levels of a divalent cation, and appears distinct from chloroplast Isoprene synthases. When grown in a bioreactor, B. subtilis cells released Isoprene in three distinct phases; using permeabilized cells, it was shown that Isoprene synthase activity rose and fell in parallel with each phase. These results suggest that Isoprene synthesis is highly regulated in B. subtilis and further research in this model system may shed light on the role of Isoprene formation in biological systems.
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human breath Isoprene and its relation to blood cholesterol levels new measurements and modeling
Journal of Applied Physiology, 2001Co-Authors: T Karl, Ray Fall, P Prazeller, Dagmar Mayr, Alfons Jordan, Josef Rieder, W LindingerAbstract:Numerous publications have described measurements of breath Isoprene in humans, and there has been a hope that breath Isoprene analyses could be a noninvasive diagnostic tool to assess blood cholesterol levels or cholesterol synthesis rate. However, significant analytic problems in breath Isoprene analysis and variability in Isoprene levels with age, exercise, diet, etc., have limited the usefulness of these measurements. Here, we have applied proton transfer reaction-mass spectrometry to this problem, allowing on-line detection of breath Isoprene. We show that breath Isoprene concentration increases within a few seconds after exercise is started as a result of a rapid increase in heart rate and then reaches a lower steady state when breath rate stabilizes. Additional experiments demonstrated that increases in heart rate associated with standing after reclining or sleeping are associated with increased breath Isoprene concentrations. An Isoprene gas-exchange model was developed and shows excellent fit to breath Isoprene levels measured during exercise. In a preliminary experiment, we demonstrated that atorvastatin therapy leads to a decrease in serum cholesterol and low-density-lipoprotein levels and a parallel decrease in breath Isoprene levels. This work suggests that there is constant endogenous production of Isoprene during the day and night and reaffirms the possibility that breath Isoprene can be a noninvasive marker of cholesterologenesis if care is taken to measure breath Isoprene under standard conditions at constant heart rate.
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Light-Dependent Isoprene Emission (Characterization of a Thylakoid-Bound Isoprene Synthase in Salix discolor Chloroplasts)
Plant physiology, 1996Co-Authors: Mary C Wildermuth, Ray FallAbstract:Isoprene synthase is an enzyme that is responsible for the production of the volatile C5 hydrocarbon, Isoprene, in plant leaves. Isoprene formation in numerous C3 plants is interesting because (a) large quantities of Isoprene are emitted, 5 x 1014 g of C annually, (b) a plant may release 1 to 8% of its fixed C as Isoprene, and (c) the function of plant Isoprene production is unknown. Because of the dependence of foliar Isoprene emission on light, the existence of a plastidic Isoprene synthase has been postulated. To pursue this idea, a method to isolate chloroplasts from Salix discolor was developed and shows a plastidic Isoprene synthase that is tightly bound to the thylakoid membrane and accessible to trypsin inactivation. The thylakoid-bound Isoprene synthase has catalytic properties similar to known soluble Isoprene synthases; however, the relationship between these enzymes is unknown. The discovery of a thylakoid-bound Isoprene synthase with a stromal-facing domain places it in the chloroplast, where it may be subject to numerous direct and indirect light-mediated effects. Implications for the light-dependent regulation of foliar Isoprene production and its function are presented.
Francesco Loreto - One of the best experts on this subject based on the ideXlab platform.
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Isoprene Emission in Darkness by a Facultative Heterotrophic Green Alga.
Frontiers in plant science, 2020Co-Authors: K. G. Srikanta Dani, Giuseppe Torzillo, Marco Michelozzi, Rita Baraldi, Francesco LoretoAbstract:Isoprene is a highly reactive biogenic volatile hydrocarbon that strongly influences atmospheric oxidation chemistry and secondary organic aerosol budget. Many phytoplanktons emit Isoprene like terrestrial pants. Planktonic Isoprene emission is stimulated by light and heat and is seemingly dependent on photosynthesis, as in higher plants. However, prominent Isoprene-emitting phytoplanktons are known to survive also as mixotrophs and heterotrophs. Chlorella vulgaris strain G-120, a unicellular green alga capable of both photoautotrophic and heterotrophic growth, was examined for Isoprene emission using GC-MS and real-time PTR-MS in light (+CO2) and in darkness (+glucose). Chlorella emitted Isoprene at the same rate both as a photoautotroph under light, and as an exclusive heterotroph while feeding on exogenous glucose in complete darkness. By implication, Isoprene synthesis in eukaryotic phytoplankton can be fully supported by glycolytic pathways in absence of photosynthesis, which is not the case in higher plants. Isoprene emission by chlorophyll-depleted mixotrophs and heterotrophs in darkness serves unknown functions and may contribute to anomalies in oceanic Isoprene estimates.
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response of Isoprene emission and carbon metabolism to drought in white poplar populus alba saplings
New Phytologist, 2007Co-Authors: Federico Brilli, Francesco Loreto, Manuel T. Lerdau, Csengele Barta, Alessio Fortunati, Mauro CentrittoAbstract:Summary • The mechanism uncoupling Isoprene emission and photosynthesis under drought was investigated in Populus alba saplings. • Isoprene emission, incorporation of 13C into the Isoprene molecule, Isoprene synthase (ISPS) activity, concentration and gene expression, and photosynthesis were measured as a function of the fraction of transpirable soil water (FTSW) and in plants recovering from drought. • Photosynthesis sharply declined below FTSW30 (a FTSW of 30%) and its inhibition was not caused by metabolic factors. A decline in Isoprene emission was only evident towards the FTSW endpoint. 13C incorporation into Isoprene was lower when photosynthesis was constrained by drought. ISPS activity was inhibited by mild drought, while ISPS gene expression and concentration declined in concert with Isoprene emission at the FTSW endpoint. Following rewatering, Isoprene emission was higher than, and photosynthesis was similar to, prestress values. ISPS activity and concentration, and 13C incorporation into Isoprene, also rapidly recovered to prestress values, while ISPS gene expression remained low in rewatered plants. • Our experiment revealed a larger contribution of alternative carbon sources to Isoprene emission only when photosynthesis was dramatically constrained by drought. Isoprene emission was likely controlled at the posttranscriptional level under severe drought.
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on the relationship between Isoprene emission and thermotolerance in phragmites australis leaves exposed to high temperatures and during the recovery from a heat stress
Plant Cell and Environment, 2005Co-Authors: Violeta Velikova, Francesco LoretoAbstract:Thermotolerance induced by Isoprene has been assessed during heat bursts but there is little information on the ability of endogenous Isoprene to confer thermotolerance under naturally elevated temperature, on the interaction between Isoprene-induced thermotolerance and light stress, and on the persistence of this protection in leaves recovering at lower temperatures. Moderately high temperature treatment (38 ∞ C for 1.5 h) reduced photosynthesis, stomatal conductance, and photochemical efficiency of photosystem II in Isoprene-emitting, but to a significantly lower extent than in Isoprene-inhibited Phragmites australis leaves. Isoprene inhibition and high temperature independently, as well as together, induced lipid peroxidation, increased level of H 2 O 2 , and increased catalase and peroxidase activities. However, leaves in which Isoprene emission was previously inhibited developed stronger oxidative stress under high temperature with respect to Isopreneemitting leaves. The heaviest photosynthetic stress was observed in Isoprene-inhibited leaves exposed to the brightest illumination (1500 m mol m - 2 s - 1 ) and, in general, there was also a clear additive effect of light excess on the formation of reactive oxygen species, antioxidant enzymes, and membrane damage. The increased thermotolerance capability of Isoprene-emitting leaves may be due to Isoprene ability to stabilize membranes or to scavenge reactive oxygen species. Irrespective of the mechanism by which Isoprene reduces thermal stress, Isoprene-emitting leaves are able to quickly recover after the stress. This may be an important feature for plants coping with frequent and transient temperature changes in nature.
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Isoprene produced by leaves protects the photosynthetic apparatus against ozone damage quenches ozone products and reduces lipid peroxidation of cellular membranes
Plant Physiology, 2001Co-Authors: Francesco Loreto, Violeta VelikovaAbstract:Many plants invest carbon to form Isoprene. The role of Isoprene in plants is unclear, but many experiments showed that Isoprene may have a role in protecting plants from thermal damage. A more general antioxidant action has been recently hypothesized on the basis of the protection offered by exogenous Isoprene in nonemitting plants exposed to acute ozone doses. We inhibited the synthesis of endogenous Isoprene by feeding fosmidomycin and observed that Phragmites australis leaves became more sensitive to ozone than those leaves forming Isoprene. Photosynthesis, stomatal conductance, and fluorescence parameters were significantly affected by ozone only in leaves on which Isoprene was not formed. The protective effect of Isoprene was more evident when the leaves were exposed for a long time (8 h) to relatively low (100 nL L−1) ozone levels than when the exposure was short and acute (3 h at 300 nL L−1). Isoprene quenched the amount of H2O2 formed in leaves and reduced lipid peroxidation of cellular membranes caused by ozone. These results indicate that Isoprene may exert its protective action at the membrane level, although a similar effect could be obtained if Isoprene reacted with ozone before forming active oxygen species. Irrespective of the mechanism, our results suggest that endogenous Isoprene has an important antioxidant role in plants.
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water stress temperature and light effects on the capacity for Isoprene emission and photosynthesis of kudzu leaves
Oecologia, 1993Co-Authors: Thomas D. Sharkey, Francesco LoretoAbstract:Kudzu (Pueraria lobata (Willd) Ohwi.) is a vine which forms large, monospecific stands in disturbed areas of the southeastern United States. Kudzu also emits Isoprene, a hydrocarbon which can significantly affect atmospheric chemistry including reactions leading to tropospheric ozone. We have studied physiological aspects of Isoprene emission from kudzu so the ecological consequences of Isoprene emission can be better understood. We examined: (a) the development of Isoprene emission as leaves developed, (b) the interaction between photon flux density and temperature effects on Isoprene emission, (c) Isoprene emission during and after water stress, and (d) the induction of Isoprene emission from leaves grown at low temperature by water stress or elevated temperature. Isoprene emission under standard conditions of 1000 μmol photons·m-2·s-1 and 30°C developed only after the leaf had reached full expansion, and was not complete until up to two weeks past the point of full expansion of the leaf. The effect of temperature on Isoprene emission was much greater than found for other species, with a 10°C increase in temperature causing a eight-fold increase in the rate of Isoprene emission. Isoprene emission from kudzu was stimulated by increases in photon flux density up to 3000 μmol photons·m-2·s-1. In contrast, photosynthesis of kudzu was saturated at less than 1000 μmol·m-2·s-1 photon flux density and was reduced at high temperature, so that up to 20% of the carbon fixed in photosynthesis was reemitted as Isoprene gas at 1000 μmol photons·m-2·s-1 and 35°C. Withholding water caused photosynthesis to decline nearly to zero after several days but had a much smaller effect on Isoprene emission. Following the relief of water stress, photosynthesis recovered to the prestress level but Isoprene emission increased to about five times the prestress rate. At 1000 μmol photons·m-2·s-1 and 35°C as much as 67% of the carbon fixed in photosynthesis was reemitted as Isoprene eight days after water stress. Leaves grown at less than 20°C did not make Isoprene until an inductive treatment was given. Inductive treatments included growth at 24°C, leaf temperature of 30°C for 5 h, or witholding water from plants. With the new information on temperature and water stress effects on Isoprene emission, we speculate that Isoprene emission may help plants cope with stressful conditions.
