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Hisashi Kato-noguchi - One of the best experts on this subject based on the ideXlab platform.
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Allelopathic Potential of Pueraria thunbergiana
Biologia Plantarum, 2003Co-Authors: Hisashi Kato-noguchiAbstract:The allelopathic potential of Pueraria thunbergiana was investigated under laboratory conditions. The powder of freeze-dried leaves of P. thunbergiana inhibited the germination and the growth of roots and shoots of cress, lettuce, timothy and ryegrass. Significant reductions in the germination and growth of roots and shoots were observed as the powder concentration increased in all bioassays. The putative compounds causing the inhibitory effect of the powder were isolated and determined by their spectral data as cis.trans- and trans,trans-Xanthoxin
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Allelopathic substances in Pueraria thunbergiana
Phytochemistry, 2003Co-Authors: Hisashi Kato-noguchiAbstract:Abstract Leaves of Pueraria thunbergiana possess allelopathic activity and the putative compounds causing this growth inhibitory effect were isolated from their aqueous methanol extract. The chemical structures of these growth inhibitors were determined by high-resolution MS and 1H NMR spectral data as cis,trans-Xanthoxin and trans,trans-Xanthoxin. cis,trans-Xanthoxin and trans,trans-Xanthoxin inhibited the root growth of cress (Lepidium sativum L.) seedlings at concentrations greater than 0.3 and 3 μM, respectively. The doses required for 50% inhibition on the cress roots were 1.1 and 14 μM for cis,trans- and trans,trans-Xanthoxin, respectively. The concentrations of cis,trans- and trans,trans-Xanthoxin in P. thunbergiana leaves were 51.4 and 72.5 ng g−1 fresh weight, respectively. The effectiveness of cis,trans- and trans,trans-Xanthoxin on the growth inhibition and the occurrence of both Xanthoxins in P. thunbergiana suggest that Xanthoxins may contribute to the growth inhibitory effect of P. thunbergiana, and may play an important role in the allelopathy of P. thunbergiana after being released into the soil.
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RED-LIGHT-INDUCED CHANGES IN THE DISTRIBUTION OF Xanthoxin IN PEA SEEDLINGS
Biologia Plantarum, 1997Co-Authors: Hisashi Kato-noguchiAbstract:The distribution of Xanthoxin (Xan), was determined in light-grown, 20-d-old pea (Pisum sativum L. cv. Progress No. 9) seedlings. The cis,trans-Xanthoxin (c,t-Xan) and the trans,trans-Xanthoxin (t,t-Xan) were more abundant in the young leaves and terminal bud; their concentrations in leaves were 2 - 3 times those in internodes of the same nodes. After the onset of red-light-irradiation, the concentration of both Xan isomers in 7-d-old dark-grown pea seedlings increased after a 12-h lag time. The increased level of Xan was greatest in the terminal bud and decreased to lower parts of the seedlings. The ratio of c,t-Xan to t,t-Xan concentration in the seedlings was about 2:3.
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Activities of growth inhibitors isolated from light-grown dwarf pea shoots
Plant Growth Regulation, 1992Co-Authors: K. Miyamoto, Hisashi Kato-noguchi, T. HashimotoAbstract:The growth inhibitory activities of 6 endogenous growth inhibitors isolated from light-grown dwarf peas (Pisum sativum cv. Progress No. 9) were examined in the epicotyl of dark-grown seedlings of the same cultivar in the dark in order to examine the possible contribution of these compounds to the growth inhibition brought about by red light. The activities of these natural inhibitors, including two A-2α and A-2β of as yet undetermined structure, were compared with those of synthetic growth retardants and benzyladenine. Samples were applied directly into the epicotyls via a glass capillary tube. In 24-h tests doses for a 25% inhibition (I25) were: A-2α, 4.3 × 10-2: cis-Xanthoxin, 1.2 × 10-1 ; A-2β, 1.6 × 10-1; trans-Xanthoxin, 1.2; R,S-dihydromaleimide, 3.5 × 102 and pisatin, 4.0 × 102 nmol plant-1 . In 72-h tests, I25's were: benzyladenine, 1.5; AMO-1618 (ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate), 2.4; R,S-dihydromaleimide, 4.0 × 102 and CCC (chlorocholine chloride), 1.1 × 103 nmol plant-1. β-D-Glucosyl-R-dihydromaleimide had no activity at all. Benzyladenine caused the thickening as well as elongation inhibition of the epicotyls of intact plants. The possible involvement of A-2α and β in the red light growth inhibition of dwarf peas is discussed.
Jan A D Zeevaart - One of the best experts on this subject based on the ideXlab platform.
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Update on Abscisic Acid Biosynthesis Elucidation of the Indirect Pathway of Abscisic Acid
2013Co-Authors: Biosynthesis Mutants, Steven H. Schwartz, Xiaoqiong Qin, Jan A D ZeevaartAbstract:Abscisic acid (ABA) was discovered independently by several groups in the early 1960s. Originally believed to be involved in the abscission of fruit and dormancy of woody plants, the role of ABA in these processes is still not clear. ABA is, however, necessary for seed development, adaptation to several abiotic stresses, and sugar sensing. The regulation of these processes is in large part mediated by changes in de novo synthesis of ABA. Two pathways have been proposed for the synthesis of ABA. In the “direct pathway, ” which operates in some fungi, ABA is derived from farnesyl diphosphate (Hirai et al., 2000). Because of structural similarities, an “indirect pathway ” in which ABA is produced from the cleavage of carotenoids also had been proposed (Taylor and Smith, 1967). The first committed step for ABA synthesis in plants is the oxidative cleavage of a 9-cis-epoxycarotenoid (C 40) to produce Xanthoxin (C 15) andaC 25 by-product (Fig. 1). The 4�-hydroxyl of Xanthoxin is oxidized to a ketone by an NAD-requiring enzyme. As a consequence, there is a nonenzymatic desaturation of the 2�-3 � bond and opening of the epoxide ring to form abscisic aldehyde. In the final step of the pathway, abscisic aldehyde is oxidized to ABA. Evidence for the indirect pathway in plants had initially come from a variety of biochemical studies, 18 O2-labeling experiments, and the characterization of ABA-deficient mutants. In recent years, the genes encoding enzymes for many steps in the pathway have been identified. Much of the recent work in characterizing these genes has confirmed previous biochemical studies. Advances in the elucidation of the ABA biosynthetic pathway and its regulation also have allowed the manipulation of ABA levels in transgenic plants. Of particular interest is the cloning and characterization of the nine-cis-epoxycarotenoid dioxygenases (NCEDs) that catalyze the rate-limiting step in ABA synthesis. The identification of the NCEDs also has had an impact beyond plant biology
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characterization of the 9 cis epoxycarotenoid dioxygenase gene family and the regulation of abscisic acid biosynthesis in avocado
Plant Physiology, 2000Co-Authors: Jacqueline T Chernys, Jan A D ZeevaartAbstract:Avocado (Persea americana Mill. cv Lula) is a climacteric fruit that exhibits a rise in ethylene as the fruit ripens. This rise in ethylene is followed by an increase in abscisic acid (ABA), with the highest level occurring just after the peak in ethylene production. ABA is synthesized from the cleavage of carotenoid precursors. The cleavage of carotenoid precursors produces Xanthoxin, which can subsequently be converted into ABA via ABA-aldehyde. Indirect evidence indicates that the cleavage reaction, catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED), is the regulatory step in ABA synthesis. Three genes encoding NCED cleavage-like enzymes were cloned from avocado fruit. Two genes, PaNCED1 and PaNCED3, were strongly induced as the fruit ripened. The other gene, PaNCED2, was constitutively expressed during fruit ripening, as well as in leaves. This gene lacks a predicted chloroplast transit peptide. It is therefore unlikely to be involved in ABA biosynthesis. PaNCED1 was induced by water stress, but expression of PaNCED3 was not detectable in dehydrated leaves. Recombinant PaNCED1 and PaNCED3 were capable of in vitro cleavage of 9-cis-xanthophylls into Xanthoxin and C25-apocarotenoids, but PaNCED2 was not. Taken together, the results indicate that ABA biosynthesis in avocado is regulated at the level of carotenoid cleavage. Fruit ripening involves a complex series of biochemical events in which the tissue undergoes programmed changes in texture, aroma, coloration, flavor, and firmness (Brady, 1987). Climacteric species, such as avocado (Persea americana Mill. cv Lula), are characterized by the autocatalytic production of the ripening hormone ethylene and a ripening-related transient burst in CO2 evolution (Biale and Young, 1981). In avocado the increase in ethylene production is followed by an increase in abscisic acid (ABA) levels (Adato et al., 1976). Although ethylene induces the synthesis of many genes involved in fruit ripening (Brady, 1987), it is not known whether the rise in ethylene is related to the increase in ABA in avocado. Further, the role that ABA plays in the ripening process is also unknown. Ripening avocado fruit produces high levels of ABA and thus provides an ideal system in which to study the regulation of ABA biosynthesis.
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Genetic control of abscisic acid biosynthesis in maize
Proceedings of the National Academy of Sciences of the United States of America, 1997Co-Authors: Bao-cai Tan, Jan A D Zeevaart, Steven H. Schwartz, Donald R. MccartyAbstract:Abscisic acid (ABA), an apocarotenoid synthesized from cleavage of carotenoids, regulates seed maturation and stress responses in plants. The viviparous seed mutants of maize identify genes involved in synthesis and perception of ABA. Two alleles of a new mutant, viviparous14 (vp14), were identified by transposon mutagenesis. Mutant embryos had normal sensitivity to ABA, and detached leaves of mutant seedlings showed markedly higher rates of water loss than those of wild type. The ABA content of developing mutant embryos was 70% lower than that of wild type, indicating a defect in ABA biosynthesis. vp14 embryos were not deficient in epoxy-carotenoids, and extracts of vp14 embryos efficiently converted the carotenoid cleavage product, Xanthoxin, to ABA, suggesting a lesion in the cleavage reaction. vp14 was cloned by transposon tagging. The VP14 protein sequence is similar to bacterial lignostilbene dioxygenases (LSD). LSD catalyzes a double-bond cleavage reaction that is closely analogous to the carotenoid cleavage reaction of ABA biosynthesis. Southern blots indicated a family of four to six related genes in maize. The Vp14 mRNA is expressed in embryos and roots and is strongly induced in leaves by water stress. A family of Vp14-related genes evidently controls the first committed step of ABA biosynthesis. These genes are likely to play a key role in the developmental and environmental control of ABA synthesis in plants.
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Specific Oxidative Cleavage of Carotenoids by VP14 of Maize
Science (New York N.Y.), 1997Co-Authors: Steven H. Schwartz, Jan A D Zeevaart, Bao-cai Tan, Douglas A. Gage, Donald R. MccartyAbstract:The plant growth regulator abscisic acid (ABA) is formed by the oxidative cleavage of an epoxy-carotenoid. The synthesis of other apocarotenoids, such as vitamin A in animals, may occur by a similar mechanism. In ABA biosynthesis, oxidative cleavage is the first committed reaction and is believed to be the key regulatory step. A new ABA-deficient mutant of maize has been identified and the corresponding gene, Vp14 , has been cloned. The recombinant VP14 protein catalyzes the cleavage of 9- cis -epoxy-carotenoids to form C 25 apo-aldehydes and Xanthoxin, a precursor of ABA in higher plants.
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Biochemical Characterization of the aba2 and aba3 Mutants in Arabidopsis thaliana
Plant physiology, 1997Co-Authors: Steven H. Schwartz, Karen M. Léon-kloosterziel, Maarten Koornneef, Jan A D ZeevaartAbstract:Abscisic acid (ABA)-deficient mutants in a variety of species have been identified by screening for precocious germination and a wilty phenotype. Mutants at two new loci, aba2 and aba3, have recently been isolated in Arabidopsis thaliana (L.) Heynh. (K.M. Leon-Kloosterziel, M. Alvarez-Gil, G.J. Ruijs, S.E. Jacobsen, N.E. Olszewski, S.H. Schwartz, J.A.D. Zeevaart, M. Koornneef [1996] Plant J 10: 655–661), and the biochemical characterization of these mutants is presented here. Protein extracts from aba2 and aba3 plants displayed a greatly reduced ability to convert Xanthoxin to ABA relative to the wild type. The next putative intermediate in ABA synthesis, ABA-aldehyde, was efficiently converted to ABA by extracts from aba2 but not by extracts from aba3 plants. This indicates that the aba2 mutant is blocked in the conversion of Xanthoxin to ABA-aldehyde and that aba3 is impaired in the conversion of ABA-aldehyde to ABA. Extracts from the aba3 mutant also lacked additional activities that require a molybdenum cofactor (Moco). Nitrate reductase utilizes a Moco but its activity was unaffected in extracts from aba3 plants. Moco hydroxylases in animals require a desulfo moiety of the cofactor. A sulfido ligand can be added to the Moco by treatment with Na2S and dithionite. Treatment of aba3 extracts with Na2S restored ABA-aldehyde oxidase activity. Therefore, the genetic lesion in aba3 appears to be in the introduction of S into the Moco.
Takayuki Oritani - One of the best experts on this subject based on the ideXlab platform.
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microbial hydroxylation of and 2z 4e 5 1 2 epoxy 2 6 6 trimethylcyclohexyl 3 methyl 2 4 pentadienoic acid into and Xanthoxin acid by cunninghamella echinulata
Bioscience Biotechnology and Biochemistry, 2001Co-Authors: Ryou Okazaki, Takayuki Oritani, Yoshihiro Hara, Hirotaka YamamotoAbstract:Microbial hydroxylation of (±)-(2Z,4E)-5-(1',2'-epoxy-2',6',6'-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid (3a) with Cercospora cruenta, a fungus producing (+)-abscisic acid, gave a four- stereoisomeric mixture consisting of (+)- and (−)-Xanthoxin acid (4a), and (+)- and (−)-epi-Xanthoxin acid (5a) by an HPLC analysis with a chiral column. Screening of the microorganisms capable of oxidizing (±)-3a showed that Cunninghamella echinulata stereoselectively oxidized (±)-3a to Xanthoxin acid (4a) with the some degree of enantioselectivity as (−)-3a to (−)-4a.
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Microbial hydroxylation of (+/-)- and (-)-(2Z,4E)-5-(1',2'-epoxy-2',6',6'-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid into (+/-)- and (-)-Xanthoxin acid by Cunninghamella echinulata.
Bioscience biotechnology and biochemistry, 2001Co-Authors: Ryou Okazaki, Takayuki Oritani, Yoshihiro Hara, Hirotaka YamamotoAbstract:Microbial hydroxylation of (±)-(2Z,4E)-5-(1',2'-epoxy-2',6',6'-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid (3a) with Cercospora cruenta, a fungus producing (+)-abscisic acid, gave a four- stereoisomeric mixture consisting of (+)- and (−)-Xanthoxin acid (4a), and (+)- and (−)-epi-Xanthoxin acid (5a) by an HPLC analysis with a chiral column. Screening of the microorganisms capable of oxidizing (±)-3a showed that Cunninghamella echinulata stereoselectively oxidized (±)-3a to Xanthoxin acid (4a) with the some degree of enantioselectivity as (−)-3a to (−)-4a.
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Isomeric Ratio and Level of Xanthoxin in Tomato Plants Measured by a New Analytical Method
Bioscience Biotechnology and Biochemistry, 1997Co-Authors: Hirotaka Yamamoto, Takayuki OritaniAbstract:The isomeric ratio and level of natural Xanthoxin (XAN) in tomato plants (Lycopersicon esculentum) were examined by a more reliable analytical method than has been reported before. Efforts were made to avoid artificial isomerization between c-XAN and t-XAN throughout the isolation, derivatization and GC-MS procedures. Natural XAN was separated from contaminating chlorophylls before rev. HPLC purification, derivatized to abscisic acid methyl ester (MeABA) in four chemical steps, and quantified with the deuterium-labeled internal standards on clear and reproducible full GC-EI-MS. It was revealed that the isomeric composition of natural XAN was exclusively shifted to c-XAN. The level of c-XAN was higher and more significantly induced by water stress in older plants. The significant role of c-XAN as an ABA biosynthetic precursor is suggested.
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Stereoselectivity in the biosynthetic conversion of Xanthoxin into abscisic acid
Planta, 1996Co-Authors: Hiroshi Yamomoto, Takayuki OritaniAbstract:All stereoisomers of Xanthoxin (XAN) and abscisic aldehyde (ABA-aldehyde) were prepared from ( R ) and ( S )-4-hydroxy-β-cyclogeraniol via asymmetric epoxidation. Their stomatal closure activities were measured on epidermal strips of Commelina communis L. Natural ( S )-ABA-aldehyde showed strong activity comparable to that of ( S )-abscisic acid (ABA). Natural (1′ S , 2′ R , 4′ S )XAN and (1′ S , 2′ R , 4′ R )- epi -XAN also induced stomatal closure at high concentrations. On the other hand, unnatural (1′ R )-enantiomers of XAN, epi -XAN, and ABA-aldehyde were not effective. To further examine the Stereoselectivity on the biosynthetic pathway to ABA, deuterium-labeled substrates were prepared and fed to Lycopersicon esculentum Mill, under non-stressed or water-stressed conditions. Substantial incorporations into ABA were observed in the cases of natural (1′ S , 2′ R , 4′ S )-XAN, (1′ S , 2′ R , 4′ R )- epi -XAN and both enantiomers of ABA-aldehyde, leading to the following conclusions. The negligible effect of unnatural (1′ R )-enantiomers of XAN, epi -XAN and ABA-aldehyde can be explained by their own biological inactivity and/or their conversion to inactive ( R )-ABA. Even in the isolated epidermal strips, putative aldehyde oxidase activity is apparently sufficient to convert ABA-aldehyde to ABA while the activity of XAN dehydrogenase seems very weak. The stereochemistry of the 1′, 2′-epoxide is very important for the XAN-dehydrogenase while this enzyme is less selective regarding the 4′-hydrdxyl group of XAN and converts both (1′ S , 2′ R , 4′ S )-XAN and (1′ S , 2′ R , 4′ R )- epi -XAN to ( S )-ABA-aldehyde. Abscisic aldehyde oxidase can nonstereoselectively convert both ( S ) and ( R )-ABA-aldehyde to biologically active ( S ) and inactive ( R )-ABA, respectively.
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Derivatization and deuterium labeling of Xanthoxin
Tetrahedron Letters, 1995Co-Authors: Hiroshi Yamamoto, Takayuki OritaniAbstract:Abstract Xanthoxin was derivatized to abscisic acid methyl ester via oxidative esterification. Deuterium labeling by LiAlD 4 and D 2 O provided a useful internal standard for the quantificatin of natural Xanthoxin level on GC-MS in combination with the new derivatization method.
Donald R. Mccarty - One of the best experts on this subject based on the ideXlab platform.
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Characterization of the ABA‐deficient tomato mutant notabilis and its relationship with maize Vp14
The Plant journal : for cell and molecular biology, 1999Co-Authors: Alan Burbidge, Donald R. Mccarty, Teresa Grieve, Alison C. Jackson, Andrew Thompson, Ian TaylorAbstract:The notabilis (not) mutant of tomato has a wilty phenotype due to a deficiency in the levels of the plant hormone abscisic acid (ABA). The mutant appears to have a defect in a key control step in ABA biosynthesis--the oxidative cleavage of a 9-cis xanthophyll precursor to form the C15 intermediate, Xanthoxin. A maize mutant, viviparous 14 (vp14) was recently obtained by transposon mutagenesis. This maize genetic lesion also affects the oxidative cleavage step in ABA synthesis. Degenerate primers for PCR, based on the VP14 predicted amino acid sequence, have been used to provide probes for screening a wilt-related tomato cDNA library. A full-length cDNA clone was identified which is specific to the not gene locus. The ORFs of the tomato cDNA and maize Vp14 are very similar, apart from parts of their N-terminal sequences. The not mutation has been characterized at the DNA level. A specific A/T base pair deletion of the coding sequence has resulted in a frameshift mutation, indicating that not is a null mutant. This observation is discussed in connection with the relatively mild phenotype exhibited by not mutant homozygotes.
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Genetic control of abscisic acid biosynthesis in maize
Proceedings of the National Academy of Sciences of the United States of America, 1997Co-Authors: Bao-cai Tan, Jan A D Zeevaart, Steven H. Schwartz, Donald R. MccartyAbstract:Abscisic acid (ABA), an apocarotenoid synthesized from cleavage of carotenoids, regulates seed maturation and stress responses in plants. The viviparous seed mutants of maize identify genes involved in synthesis and perception of ABA. Two alleles of a new mutant, viviparous14 (vp14), were identified by transposon mutagenesis. Mutant embryos had normal sensitivity to ABA, and detached leaves of mutant seedlings showed markedly higher rates of water loss than those of wild type. The ABA content of developing mutant embryos was 70% lower than that of wild type, indicating a defect in ABA biosynthesis. vp14 embryos were not deficient in epoxy-carotenoids, and extracts of vp14 embryos efficiently converted the carotenoid cleavage product, Xanthoxin, to ABA, suggesting a lesion in the cleavage reaction. vp14 was cloned by transposon tagging. The VP14 protein sequence is similar to bacterial lignostilbene dioxygenases (LSD). LSD catalyzes a double-bond cleavage reaction that is closely analogous to the carotenoid cleavage reaction of ABA biosynthesis. Southern blots indicated a family of four to six related genes in maize. The Vp14 mRNA is expressed in embryos and roots and is strongly induced in leaves by water stress. A family of Vp14-related genes evidently controls the first committed step of ABA biosynthesis. These genes are likely to play a key role in the developmental and environmental control of ABA synthesis in plants.
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Specific Oxidative Cleavage of Carotenoids by VP14 of Maize
Science (New York N.Y.), 1997Co-Authors: Steven H. Schwartz, Jan A D Zeevaart, Bao-cai Tan, Douglas A. Gage, Donald R. MccartyAbstract:The plant growth regulator abscisic acid (ABA) is formed by the oxidative cleavage of an epoxy-carotenoid. The synthesis of other apocarotenoids, such as vitamin A in animals, may occur by a similar mechanism. In ABA biosynthesis, oxidative cleavage is the first committed reaction and is believed to be the key regulatory step. A new ABA-deficient mutant of maize has been identified and the corresponding gene, Vp14 , has been cloned. The recombinant VP14 protein catalyzes the cleavage of 9- cis -epoxy-carotenoids to form C 25 apo-aldehydes and Xanthoxin, a precursor of ABA in higher plants.
Steven H. Schwartz - One of the best experts on this subject based on the ideXlab platform.
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Update on Abscisic Acid Biosynthesis Elucidation of the Indirect Pathway of Abscisic Acid
2013Co-Authors: Biosynthesis Mutants, Steven H. Schwartz, Xiaoqiong Qin, Jan A D ZeevaartAbstract:Abscisic acid (ABA) was discovered independently by several groups in the early 1960s. Originally believed to be involved in the abscission of fruit and dormancy of woody plants, the role of ABA in these processes is still not clear. ABA is, however, necessary for seed development, adaptation to several abiotic stresses, and sugar sensing. The regulation of these processes is in large part mediated by changes in de novo synthesis of ABA. Two pathways have been proposed for the synthesis of ABA. In the “direct pathway, ” which operates in some fungi, ABA is derived from farnesyl diphosphate (Hirai et al., 2000). Because of structural similarities, an “indirect pathway ” in which ABA is produced from the cleavage of carotenoids also had been proposed (Taylor and Smith, 1967). The first committed step for ABA synthesis in plants is the oxidative cleavage of a 9-cis-epoxycarotenoid (C 40) to produce Xanthoxin (C 15) andaC 25 by-product (Fig. 1). The 4�-hydroxyl of Xanthoxin is oxidized to a ketone by an NAD-requiring enzyme. As a consequence, there is a nonenzymatic desaturation of the 2�-3 � bond and opening of the epoxide ring to form abscisic aldehyde. In the final step of the pathway, abscisic aldehyde is oxidized to ABA. Evidence for the indirect pathway in plants had initially come from a variety of biochemical studies, 18 O2-labeling experiments, and the characterization of ABA-deficient mutants. In recent years, the genes encoding enzymes for many steps in the pathway have been identified. Much of the recent work in characterizing these genes has confirmed previous biochemical studies. Advances in the elucidation of the ABA biosynthetic pathway and its regulation also have allowed the manipulation of ABA levels in transgenic plants. Of particular interest is the cloning and characterization of the nine-cis-epoxycarotenoid dioxygenases (NCEDs) that catalyze the rate-limiting step in ABA synthesis. The identification of the NCEDs also has had an impact beyond plant biology
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Genetic control of abscisic acid biosynthesis in maize
Proceedings of the National Academy of Sciences of the United States of America, 1997Co-Authors: Bao-cai Tan, Jan A D Zeevaart, Steven H. Schwartz, Donald R. MccartyAbstract:Abscisic acid (ABA), an apocarotenoid synthesized from cleavage of carotenoids, regulates seed maturation and stress responses in plants. The viviparous seed mutants of maize identify genes involved in synthesis and perception of ABA. Two alleles of a new mutant, viviparous14 (vp14), were identified by transposon mutagenesis. Mutant embryos had normal sensitivity to ABA, and detached leaves of mutant seedlings showed markedly higher rates of water loss than those of wild type. The ABA content of developing mutant embryos was 70% lower than that of wild type, indicating a defect in ABA biosynthesis. vp14 embryos were not deficient in epoxy-carotenoids, and extracts of vp14 embryos efficiently converted the carotenoid cleavage product, Xanthoxin, to ABA, suggesting a lesion in the cleavage reaction. vp14 was cloned by transposon tagging. The VP14 protein sequence is similar to bacterial lignostilbene dioxygenases (LSD). LSD catalyzes a double-bond cleavage reaction that is closely analogous to the carotenoid cleavage reaction of ABA biosynthesis. Southern blots indicated a family of four to six related genes in maize. The Vp14 mRNA is expressed in embryos and roots and is strongly induced in leaves by water stress. A family of Vp14-related genes evidently controls the first committed step of ABA biosynthesis. These genes are likely to play a key role in the developmental and environmental control of ABA synthesis in plants.
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Specific Oxidative Cleavage of Carotenoids by VP14 of Maize
Science (New York N.Y.), 1997Co-Authors: Steven H. Schwartz, Jan A D Zeevaart, Bao-cai Tan, Douglas A. Gage, Donald R. MccartyAbstract:The plant growth regulator abscisic acid (ABA) is formed by the oxidative cleavage of an epoxy-carotenoid. The synthesis of other apocarotenoids, such as vitamin A in animals, may occur by a similar mechanism. In ABA biosynthesis, oxidative cleavage is the first committed reaction and is believed to be the key regulatory step. A new ABA-deficient mutant of maize has been identified and the corresponding gene, Vp14 , has been cloned. The recombinant VP14 protein catalyzes the cleavage of 9- cis -epoxy-carotenoids to form C 25 apo-aldehydes and Xanthoxin, a precursor of ABA in higher plants.
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Biochemical Characterization of the aba2 and aba3 Mutants in Arabidopsis thaliana
Plant physiology, 1997Co-Authors: Steven H. Schwartz, Karen M. Léon-kloosterziel, Maarten Koornneef, Jan A D ZeevaartAbstract:Abscisic acid (ABA)-deficient mutants in a variety of species have been identified by screening for precocious germination and a wilty phenotype. Mutants at two new loci, aba2 and aba3, have recently been isolated in Arabidopsis thaliana (L.) Heynh. (K.M. Leon-Kloosterziel, M. Alvarez-Gil, G.J. Ruijs, S.E. Jacobsen, N.E. Olszewski, S.H. Schwartz, J.A.D. Zeevaart, M. Koornneef [1996] Plant J 10: 655–661), and the biochemical characterization of these mutants is presented here. Protein extracts from aba2 and aba3 plants displayed a greatly reduced ability to convert Xanthoxin to ABA relative to the wild type. The next putative intermediate in ABA synthesis, ABA-aldehyde, was efficiently converted to ABA by extracts from aba2 but not by extracts from aba3 plants. This indicates that the aba2 mutant is blocked in the conversion of Xanthoxin to ABA-aldehyde and that aba3 is impaired in the conversion of ABA-aldehyde to ABA. Extracts from the aba3 mutant also lacked additional activities that require a molybdenum cofactor (Moco). Nitrate reductase utilizes a Moco but its activity was unaffected in extracts from aba3 plants. Moco hydroxylases in animals require a desulfo moiety of the cofactor. A sulfido ligand can be added to the Moco by treatment with Na2S and dithionite. Treatment of aba3 extracts with Na2S restored ABA-aldehyde oxidase activity. Therefore, the genetic lesion in aba3 appears to be in the introduction of S into the Moco.
