The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform
Lutz A Eichacker - One of the best experts on this subject based on the ideXlab platform.
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Printed in U.S. A. In Vitro Synthesis of Chlorophyll A in the Dark Triggers Accumulation of Chlorophyll A Apoproteins in Barley Etioplasts”
2015Co-Authors: Lutz A Eichacker, Jiirgen Solls, Petra Lauterbachs, Wolfhart Riidigerl, Robert R. Kleinll, John E. MulletAbstract:An in vitro translation system using lysed Etioplasts was developed to test if the accumulation of plastid-encoded chlorophyll a apoproteins is dependent on the de novo synthesis of chlorophyll a. The P700 apopro-teins, CP47 and CP43, were not radiolabeled in pulse-chase translation assays employing lysed Etioplasts in the absence of added chlorophyll precursors. When chlorophyllide a plus phytylpyrophosphate were added to lysed Etioplast translation assays in the dark, chlo-rophyll a was synthesized and radiolabeled P700 apo-proteins, CP47 and CP43, and a protein which comi-grates with D1 accumulated. Chlorophyllide a or pby-tylpyrophosphate added separately to the translation assay in darkness did not induce chlorophyll a forma-tion or chlorophyll a apoprotein accumulation. Chlo
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Assembly of the D1 precursor in monomeric photosystem II reaction center precomplexes precedes chlorophyll a-triggered accumulation of reaction center II in barley Etioplasts.
The Plant cell, 1999Co-Authors: Bernd Müller, Lutz A EichackerAbstract:Assembly of plastid-encoded chlorophyll binding proteins of photosystem II (PSII) was studied in etiolated barley seedlings and isolated Etioplasts and either the absence or presence of de novo chlorophyll synthesis. De novo assembly of reaction center complexes in Etioplasts was characterized by immunological analysis of protein complexes solubilized from inner Etioplast membranes and separated in sucrose density gradients. Previously characterized membrane protein complexes from chloroplasts were utilized as molecular mass standards for sucrose density gradient separation analysis. In etiolated seedlings, induction of chlorophyll a synthesis resulted in the accumulation of D1 in a dimeric PSII reaction center (RCII) complex. In isolated Etioplasts, de novo chlorophyll a synthesis directed accumulation of D1 precursor in a monomeric RCII precomplex that also included D2 and cytochrome b 559 . Chlorophyll a synthesis that was chemically prolonged in darkness neither increased the yield of RCII monomers nor directed assembly of RCII dimers in Etioplasts. We therefore conclude that in Etioplasts, assembly of the D1 precursor in monomeric RCII precomplexes precedes chlorophyll a –triggered accumulation of reaction center monomers.
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light harvesting chlorophyll a b binding protein stably inserts into Etioplast membranes supplemented with zn pheophytin a b
Journal of Biological Chemistry, 1997Co-Authors: Andrea Kuttkat, Lutz A Eichacker, Ingrid Edhofer, Harald PaulsenAbstract:Abstract Light-harvesting chlorophylla/b-binding protein, LHCP, or its precursor, pLHCP, cannot be stably inserted into barley Etioplast membranes in vitro. However, when these Etioplast membranes are supplemented with the chlorophyll analogs Zn-pheophytin a/b, synthesizedin situ from Zn-pheophorbide a/b and digeranyl pyrophosphate, pLHCP is inserted into a protease-resistant state. This proves that chlorophyll is the only component lacking in Etioplast membranes that is necessary for stable LHCP insertion. Synthesis of Zn-pheophytin b alone promotes insertion of LHCP in vitro into a protease-resistant state, whereas synthesis of Zn-pheophytin a alone does not. Insertion of pLHCP into Etioplast membranes can also be stimulated by adding chlorophyll a and chlorophyll b to the membranes, albeit at a significantly lower efficiency as compared with Zn-pheophytin a/b synthesized in situ. When pLHCP is inserted into chlorophyll- or Zn-pheophytin-supplemented Etioplast membranes and then assayed with protease, only the protease digestion product indicative of the monomeric major light-harvesting chlorophyll a/b complex (LHCII) is found but not the one indicating trimeric complexes. In this respect, chlorophyll- or Zn-pheophytin-supplemented Etioplast membranes resemble thylakoid membranes at an early greening stage: pLHCP inserted into plastid membranes from greening barley is assembled into trimeric LHCII only after more than 1 h of greening.
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Cryopreservation of Chlorophyll Synthesis and Apoprotein Stabilization in Barley Etioplasts.
Plant physiology, 1996Co-Authors: Lutz A Eichacker, Ingrid Edhofer, Gerhard WannerAbstract:Methods for the cryopreservation of protein import and integration in pea chloroplasts and of protein import or protein synthesis in tobacco mitochondria were modified to yield enzymatically active cryopreserved Etioplasts from barley (Hordeum vulgare L.). The cryoprotectants ethylene glycol and dimethy sulfoxide were about 64 and 77% effective, respectively, for the cryopreservation of Etioplast intactness. Phototransformation of protochlorophyllide a, esterification of chlorophyllide a or zinc-pheophorbide a, and stabilization of the de novo synthesized plastid-encoded chlorophyll-apoproteins P700, CP47, CP43, D2, and D1 were successfully preserved in liquid nitrogen. Cryopreservation of freshly prepared intact Etioplasts completely retained enzymatic activities for accumulation of chlorophyll a or resulted in a slightly decreased yield of zinc-pheophytin a.
D. Di Baccio - One of the best experts on this subject based on the ideXlab platform.
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Impaired carotenogenesis can affect organization and functionality of Etioplast membranes
Physiologia Plantarum, 2004Co-Authors: Isabella Moro, D. Di Baccio, Mike Frank Quartacci, Flavia Navari-izzo, Wolfhart Rudiger, Francesca Dalla Vecchia, Nicoletta La Rocca, Nicoletta RascioAbstract:The effects of impaired carotenogenesis on plastid membrane organization, functionality and stability were studied in etiolated barley plants grown at 20 and 30°C. The plants were treated with norflurazon or amitrole, two herbicides affecting phytoene desaturation and lycopene cyclization, respectively. At 20°C, the amitrole-treated Etioplasts, which accumulated lycopene in their inner membranes, exhibited disorganized prolamellar bodies, containing a prevalent form of non-phototransformable protochlorophyllide (Pchlide). They also showed a certain difficulty in reducing the phototransformable pigment to chlorophyllide when exposed to light, and were unable to reform the active ternary complex [protochlorophyllide-oxidoreductase (POR)-Pchlide-NADPH] when placed back in darkness. No ultrastructural alterations were found in norflurazon-treated Etioplasts, with carotenogenesis inhibited at the phytoene desaturation step. In these latter organelles, Pchlide, whose forms were comparable with those of the control Etioplasts, was photoreduced quickly after illumination and the ternary complex was reformed during a subsequent dark period. Thus, the impaired carotenogenesis leading to the accumulation of lycopene showed greater interference with the Etioplast membrane arrangement and functionality than did the earlier interruption of the biosynthetic pathway at the phytoene level. This might be due to the different interactions of the distinct carotenoid precursors with other membrane components. However, in Etioplasts of norflurazon-treated plants, a rise in growth temperature caused a partial demolition of prolamellar bodies, showing a lowered thermostability of the carotenoid-deficient membranes. This latter effect strengthens the concept that a correct and complete carotenogenesis pathway, leading to the synthesis of polar carotenoids (i.e. xanthophylls), is required for the maintenance of stable plastid membranes.
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Bleaching herbicide effects on plastids of dark‐grown plants: lipid composition of Etioplasts in amitrole and norflurazon‐treated barley leaves
Journal of Experimental Botany, 2002Co-Authors: D. Di Baccio, Mike Frank Quartacci, F. Dalla Vecchia, N. La Rocca, Nicoletta Rascio, Flavia Navari-izzoAbstract:The effects of the bleaching herbicides amitrole (125 mM) and norflurazon (100 mM) on Etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 ∞ Co r 30∞ Ci n darkness. Total lipid, glycolipid and phospholipid contents of control Etioplasts were increased at 30 ∞C in comparison with those at 20 ∞C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated Etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the Etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 ∞C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated Etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 ∞C and norflurazon at 30 ∞C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of Etioplasts and the interaction between the pigment‐protein complex, protochlorophyllide‐ NADPH‐protochlorophyllide oxidoreductase, and polar lipids are discussed.
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bleaching herbicide effects on plastids of dark grown plants lipid composition of Etioplasts in amitrole and norflurazon treated barley leaves
Journal of Experimental Botany, 2002Co-Authors: D. Di Baccio, Mike Frank Quartacci, N. La Rocca, Nicoletta Rascio, Dalla F Vecchia, F NavariizzoAbstract:The effects of the bleaching herbicides amitrole (125 mM) and norflurazon (100 mM) on Etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 ∞ Co r 30∞ Ci n darkness. Total lipid, glycolipid and phospholipid contents of control Etioplasts were increased at 30 ∞C in comparison with those at 20 ∞C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated Etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the Etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 ∞C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated Etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 ∞C and norflurazon at 30 ∞C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of Etioplasts and the interaction between the pigment‐protein complex, protochlorophyllide‐ NADPH‐protochlorophyllide oxidoreductase, and polar lipids are discussed.
Nicoletta Rascio - One of the best experts on this subject based on the ideXlab platform.
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Impaired carotenogenesis can affect organization and functionality of Etioplast membranes
Physiologia Plantarum, 2004Co-Authors: Isabella Moro, D. Di Baccio, Mike Frank Quartacci, Flavia Navari-izzo, Wolfhart Rudiger, Francesca Dalla Vecchia, Nicoletta La Rocca, Nicoletta RascioAbstract:The effects of impaired carotenogenesis on plastid membrane organization, functionality and stability were studied in etiolated barley plants grown at 20 and 30°C. The plants were treated with norflurazon or amitrole, two herbicides affecting phytoene desaturation and lycopene cyclization, respectively. At 20°C, the amitrole-treated Etioplasts, which accumulated lycopene in their inner membranes, exhibited disorganized prolamellar bodies, containing a prevalent form of non-phototransformable protochlorophyllide (Pchlide). They also showed a certain difficulty in reducing the phototransformable pigment to chlorophyllide when exposed to light, and were unable to reform the active ternary complex [protochlorophyllide-oxidoreductase (POR)-Pchlide-NADPH] when placed back in darkness. No ultrastructural alterations were found in norflurazon-treated Etioplasts, with carotenogenesis inhibited at the phytoene desaturation step. In these latter organelles, Pchlide, whose forms were comparable with those of the control Etioplasts, was photoreduced quickly after illumination and the ternary complex was reformed during a subsequent dark period. Thus, the impaired carotenogenesis leading to the accumulation of lycopene showed greater interference with the Etioplast membrane arrangement and functionality than did the earlier interruption of the biosynthetic pathway at the phytoene level. This might be due to the different interactions of the distinct carotenoid precursors with other membrane components. However, in Etioplasts of norflurazon-treated plants, a rise in growth temperature caused a partial demolition of prolamellar bodies, showing a lowered thermostability of the carotenoid-deficient membranes. This latter effect strengthens the concept that a correct and complete carotenogenesis pathway, leading to the synthesis of polar carotenoids (i.e. xanthophylls), is required for the maintenance of stable plastid membranes.
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Bleaching herbicide effects on plastids of dark‐grown plants: lipid composition of Etioplasts in amitrole and norflurazon‐treated barley leaves
Journal of Experimental Botany, 2002Co-Authors: D. Di Baccio, Mike Frank Quartacci, F. Dalla Vecchia, N. La Rocca, Nicoletta Rascio, Flavia Navari-izzoAbstract:The effects of the bleaching herbicides amitrole (125 mM) and norflurazon (100 mM) on Etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 ∞ Co r 30∞ Ci n darkness. Total lipid, glycolipid and phospholipid contents of control Etioplasts were increased at 30 ∞C in comparison with those at 20 ∞C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated Etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the Etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 ∞C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated Etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 ∞C and norflurazon at 30 ∞C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of Etioplasts and the interaction between the pigment‐protein complex, protochlorophyllide‐ NADPH‐protochlorophyllide oxidoreductase, and polar lipids are discussed.
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bleaching herbicide effects on plastids of dark grown plants lipid composition of Etioplasts in amitrole and norflurazon treated barley leaves
Journal of Experimental Botany, 2002Co-Authors: D. Di Baccio, Mike Frank Quartacci, N. La Rocca, Nicoletta Rascio, Dalla F Vecchia, F NavariizzoAbstract:The effects of the bleaching herbicides amitrole (125 mM) and norflurazon (100 mM) on Etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 ∞ Co r 30∞ Ci n darkness. Total lipid, glycolipid and phospholipid contents of control Etioplasts were increased at 30 ∞C in comparison with those at 20 ∞C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated Etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the Etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 ∞C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated Etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 ∞C and norflurazon at 30 ∞C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of Etioplasts and the interaction between the pigment‐protein complex, protochlorophyllide‐ NADPH‐protochlorophyllide oxidoreductase, and polar lipids are discussed.
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Amitrole effects on barley Etioplasts.
Journal of Plant Physiology, 1996Co-Authors: Nicoletta Rascio, Francesca Dalla Vecchia, Laura Agnolucci, Roberto Barbato, Vinicio Tassani, Giorgio CasadoroAbstract:Summary The effects of amitrole-inhibited carotenogenesis on the differentiation of Etioplasts have been investigated in barley plants grown either at 20°C or 30°C in darkness. Amitrole drastically impaired carotenoid synthesis in plants grown at 20°C and this effect was paralleled by extensive uitrastructural alterations in the Etioplasts. Protochlorophyllide oxidoreductase was found in the badly arranged membranes together with abnormally high quantities of protochlorophyllide, essentially present as non-phototransformable pigment. Growing plants at 30°C caused a remarkable improvement in the carotenoid synthesis, which was accompanied by a normalization of all the other parameters analysed. The parallelism observed between correct carotenoid synthesis and normal Etioplast development suggests that, as in chloroplasts, also in the dark-grown organelles, the carotenoids carry out a structural function, playing a role in the establishment of the regular organization of the inner membrane system.
Gregory A Armstrong - One of the best experts on this subject based on the ideXlab platform.
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arabidopsis light dependent protochlorophyllide oxidoreductase a pora is essential for normal plant growth and development
Plant Molecular Biology, 2012Co-Authors: Troy Paddock, Klaus Apel, Daniel Lima, Mary E Mason, Gregory A ArmstrongAbstract:During skotomorphogenesis in angiosperms, NADPH:protochlorophyllide oxidoreductase (POR) forms an aggregate of photolabile NADPH-POR-protochlorophyllide (Pchlide) ternary complexes localized to the prolamellar bodies within Etioplasts. During photomorphogenesis, POR catalyzes the light-dependent reduction of Pchlide a to chlorophyllide (Chlide) a, which is subsequently converted to chlorophyll (Chl). In Arabidopsis there are three structurally related POR genes, denoted PORA, PORB and PORC. The PORA and PORB proteins accumulate during skotomorphogenesis. During illumination, PORA is only transiently expressed, whereas PORB and PORC persist and are responsible for bulk Chl synthesis throughout plant development. Here we have tested whether PORA is important for skotomorphogenesis by assisting in Etioplast development, and normal photomorphogenic development. Using reverse genetic approaches, we have identified the porA-1 null mutant, which contains an insertion of the maize Dissociation transposable element in the PORA gene. Additionally, we have characterized PORA RNAi lines. The porA-1 and PORA RNAi lines display severe photoautotrophic growth defects, which can be partially rescued on sucrose-supplemented growth media. Elimination of PORA during skotomorphogenesis results in reductions in the volume and frequency of prolamellar bodies, and in photoactive Pchlide conversion. The porA-1 mutant characterization thus establishes a quantitative requirement for PORA in Etioplast development by demonstrating significant membrane ultrastructural and biochemical defects, in addition to suggesting PORA-specific functions in photomorphogenesis and plant development.
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regulation of Etioplast pigment protein complexes inner membrane architecture and protochlorophyllide a chemical heterogeneity by light dependent nadph protochlorophyllide oxidoreductases a and b
Plant Physiology, 2000Co-Authors: Fabrice Franck, Ulrich Sperling, Genevieve Frick, Klaus Apel, Babette Pochert, Barbara Van Cleve, Gregory A ArmstrongAbstract:The Etioplast of dark-grown angiosperms is characterized by the prolamellar body (PLB) inner membrane, the absence of chlorophyll, and the accumulation of divinyl and monovinyl derivatives of protochlorophyll(ide) a [Pchl(ide) a]. Either of two structurally related, but differentially expressed light-dependent NADPH:Pchlide oxidoreductases (PORs), PORA and PORB, can assemble the PLB and form dark-stable ternary complexes containing enzymatically photoactive Pchlide-F655. Here we have examined in detail whether these polypeptides play redundant roles in Etioplast differentiation by manipulating the total POR content and the PORA-to-PORB ratio of etiolated Arabidopsis seedlings using antisense and overexpression approaches. POR content correlates closely with PLB formation, the amounts, spectroscopic properties, and photoreduction kinetics of photoactive Pchlide, the ratio of photoactive Pchlide-F655 to non-photoactive Pchl(ide)-F632, and the ratio of divinyl- to monovinyl-Pchl(ide). This last result defines POR as the first endogenous protein factor demonstrated to influence the chemical heterogeneity of Pchl(ide) in angiosperms. It is intriguing that excitation energy transfer between different spectroscopic forms of Pchl(ide) in etiolated cotyledons remains largely independent of POR content. We therefore propose that the PLB contains a minimal structural unit with defined pigment stoichiometries, within which a small amount of non-photoactive Pchl(ide) transfers excitation energy to a large excess of photoactive Pchlide-F655. In addition, our data suggests that POR may bind not only stoichiometric amounts of photoactive Pchlide, but also substoichiometric amounts of non-photoactive Pchl(ide). We conclude that the typical characteristics of Etioplasts are closely related to total POR content, but not obviously to the specific presence of PORA or PORB.
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Etioplast differentiation in arabidopsis both pora and porb restore the prolamellar body and photoactive protochlorophyllide f655 to the cop1 photomorphogenic mutant
The Plant Cell, 1998Co-Authors: Ulrich Sperling, Fabrice Franck, B Van Cleve, Genevieve Frick, Klaus Apel, Gregory A ArmstrongAbstract:The Etioplast plastid type of dark-grown angiosperms is defined by the accumulation of the chlorophyll (Chl) precursor protochlorophyllide (Pchlide) and the presence of the paracrystalline prolamellar body (PLB) membrane. Both features correlate with the presence of NADPH:Pchlide oxidoreductase (POR), a light-dependent enzyme that reduces photoactive Pchlide-F655 to chlorophyllide and plays a key role in chloroplast differentiation during greening. Two differentially expressed and regulated POR enzymes, PORA and PORB, have recently been discovered in angiosperms. To investigate the hypothesis that Etioplast differentiation requires PORA, we have constitutively overexpressed PORA and PORB in the Arabidopsis wild type and in the constitutive photomorphogenic cop1-18 (previously det340) mutant, which is deficient in the PLB and Pchlide-F655. In both genetic backgrounds, POR overexpression increased PLB size, the ratio of Pchlide-F655 to nonphotoactive Pchl[ide]-F632, and the amount of Pchlide-F655. Dramatically, restoration of either PORA or PORB to the cop1 mutant led to the formation of Etioplasts containing an extensive PLB and large amounts of photoactive Pchlide-F655.
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Etioplast Differentiation in Arabidopsis: Both PORA and PORB Restore the Prolamellar Body and Photoactive Protochlorophyllide–F655 to the cop1 Photomorphogenic Mutant
The Plant cell, 1998Co-Authors: Ulrich Sperling, Fabrice Franck, B Van Cleve, Genevieve Frick, Klaus Apel, Gregory A ArmstrongAbstract:The Etioplast plastid type of dark-grown angiosperms is defined by the accumulation of the chlorophyll (Chl) precursor protochlorophyllide (Pchlide) and the presence of the paracrystalline prolamellar body (PLB) membrane. Both features correlate with the presence of NADPH:Pchlide oxidoreductase (POR), a light-dependent enzyme that reduces photoactive Pchlide-F655 to chlorophyllide and plays a key role in chloroplast differentiation during greening. Two differentially expressed and regulated POR enzymes, PORA and PORB, have recently been discovered in angiosperms. To investigate the hypothesis that Etioplast differentiation requires PORA, we have constitutively overexpressed PORA and PORB in the Arabidopsis wild type and in the constitutive photomorphogenic cop1-18 (previously det340) mutant, which is deficient in the PLB and Pchlide-F655. In both genetic backgrounds, POR overexpression increased PLB size, the ratio of Pchlide-F655 to nonphotoactive Pchl[ide]-F632, and the amount of Pchlide-F655. Dramatically, restoration of either PORA or PORB to the cop1 mutant led to the formation of Etioplasts containing an extensive PLB and large amounts of photoactive Pchlide-F655.
Flavia Navari-izzo - One of the best experts on this subject based on the ideXlab platform.
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Impaired carotenogenesis can affect organization and functionality of Etioplast membranes
Physiologia Plantarum, 2004Co-Authors: Isabella Moro, D. Di Baccio, Mike Frank Quartacci, Flavia Navari-izzo, Wolfhart Rudiger, Francesca Dalla Vecchia, Nicoletta La Rocca, Nicoletta RascioAbstract:The effects of impaired carotenogenesis on plastid membrane organization, functionality and stability were studied in etiolated barley plants grown at 20 and 30°C. The plants were treated with norflurazon or amitrole, two herbicides affecting phytoene desaturation and lycopene cyclization, respectively. At 20°C, the amitrole-treated Etioplasts, which accumulated lycopene in their inner membranes, exhibited disorganized prolamellar bodies, containing a prevalent form of non-phototransformable protochlorophyllide (Pchlide). They also showed a certain difficulty in reducing the phototransformable pigment to chlorophyllide when exposed to light, and were unable to reform the active ternary complex [protochlorophyllide-oxidoreductase (POR)-Pchlide-NADPH] when placed back in darkness. No ultrastructural alterations were found in norflurazon-treated Etioplasts, with carotenogenesis inhibited at the phytoene desaturation step. In these latter organelles, Pchlide, whose forms were comparable with those of the control Etioplasts, was photoreduced quickly after illumination and the ternary complex was reformed during a subsequent dark period. Thus, the impaired carotenogenesis leading to the accumulation of lycopene showed greater interference with the Etioplast membrane arrangement and functionality than did the earlier interruption of the biosynthetic pathway at the phytoene level. This might be due to the different interactions of the distinct carotenoid precursors with other membrane components. However, in Etioplasts of norflurazon-treated plants, a rise in growth temperature caused a partial demolition of prolamellar bodies, showing a lowered thermostability of the carotenoid-deficient membranes. This latter effect strengthens the concept that a correct and complete carotenogenesis pathway, leading to the synthesis of polar carotenoids (i.e. xanthophylls), is required for the maintenance of stable plastid membranes.
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Bleaching herbicide effects on plastids of dark‐grown plants: lipid composition of Etioplasts in amitrole and norflurazon‐treated barley leaves
Journal of Experimental Botany, 2002Co-Authors: D. Di Baccio, Mike Frank Quartacci, F. Dalla Vecchia, N. La Rocca, Nicoletta Rascio, Flavia Navari-izzoAbstract:The effects of the bleaching herbicides amitrole (125 mM) and norflurazon (100 mM) on Etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 ∞ Co r 30∞ Ci n darkness. Total lipid, glycolipid and phospholipid contents of control Etioplasts were increased at 30 ∞C in comparison with those at 20 ∞C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated Etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the Etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 ∞C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated Etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 ∞C and norflurazon at 30 ∞C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of Etioplasts and the interaction between the pigment‐protein complex, protochlorophyllide‐ NADPH‐protochlorophyllide oxidoreductase, and polar lipids are discussed.