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A. Marion-poll - One of the best experts on this subject based on the ideXlab platform.
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Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds.
Planta, 2006Co-Authors: Anne Frey, Bruno Sotta, Jean-pierre Boutin, Raphael Mercier, A. Marion-pollAbstract:Abscisic acid (ABA) is derived from epoxycarotenoid cleavage and regulates seed development and maturation. A detailed carotenoid analysis was undertaken to study the contribution of epoxycarotenoid synthesis to the regulation of ABA accumulation in Nicotiana plumbaginifolia developing seeds. Maximal accumulation of xanthophylls occurred at mid-development in wild type seeds, when total ABA levels also peaked. In contrast, in ABA-deficient mutants xanthophyll synthesis was delayed, in agreement with the retardation in seed maturation. Seed dormancy was restored in mutants impaired in the conversion of Zeaxanthin into violaxanthin by Zeaxanthin Epoxidase (ZEP), by the introduction of the Arabidopsis AtZEP gene under the control of promoters inducing expression during later stages of seed development compared to wild type NpZEP, and in dry and imbibed seeds. Alterations in the timing and level of ZEP expression did not highly affect the temporal regulation of ABA accumulation in transgenic seeds, despite notable perturbations in xanthophyll accumulation. Therefore, major regulatory control of ABA accumulation might occur downstream of epoxycarotenoid synthesis.
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Localisation and expression of Zeaxanthin Epoxidase mRNA in Arabidopsis in response to drought stress and during seed development
Australian Journal of Plant Physiology, 2001Co-Authors: Corinne Audran, S. Liotenberg, M. Gonneau, H. North, A. Frey, K. Tap-waksman, N. Vartanian, A. Marion-pollAbstract:Abscisic acid (ABA) is involved in seed development and plant adaptation to environmental stresses. ABA is synthesized from cleaved xanthophylls and Zeaxanthin Epoxidase (ZEP) is the enzyme responsible for the conversion of Zeaxanthin to violaxanthin. In this study, we have characterized the ABA1 gene (AtZEP) of Arabidopsis thaliana L. and show that this complements the aba1 mutant, defective in Zeaxanthin epoxidation. The molecular basis for two aba1 mutant alleles has been determined and the reduction in their AtZEP transcript levels correlates with the molecular defect identified. As AtZEP mRNA abundance was not affected in two other ABA-deficient mutants (aba2 and aba3) and in two ABA-insensitive mutants (abi1 and abi2), no feedback regulation of ABA biosynthesis seems to occur at the level of ZEP transcription. Steady state transcript levels increased in roots during rapid water stress as well as progressive drought stress, providing evidence that Zeaxanthin epoxidation contributed to the regulation of ABA biosynthesis in roots and consequently to the plant adaptive response to hydric stress. In seeds in situ hybridization analysis detected AtZEP mRNA in the embryo cells from the globular stage to desiccation phase. In contrast, expression of AtZEP in maternal tissues was specific to the maturation phase. These results are discussed in relation to the role of ABA both in response to drought stress and in seed development.
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N. plumbaginifolia Zeaxanthin Epoxidase transgenic lines have unaltered baseline ABA acuumulations in roots and xylem sap, but contrasting sensitivities of ABA accumulation to water deficit
Journal of Experimental Botany, 2001Co-Authors: C. Borel, A. Marion-poll, Corinne Audran, A. Frey, Francois Tardieu, Thierry SimonneauAbstract:A series of transgenic lines of Nicotiana plumbaginifolia with modified expression of Zeaxanthin Epoxidase gene ( ZEP ) provided contrasting ABA accumulation in roots and xylem sap. For mild water stress, concentration of ABA in the xylem sap ([ABA] xylem ) was clearly lower in plants underexpressing ZEP mRNA (complemented mutants and antisense transgenic lines) than in wild‐type. In well‐watered conditions, all lines presented similar [ABA] xylem and similar ABA accumulation rates in detached roots. Plants could, therefore, be grown under normal light intensities and evaporative demand. Both ZEP mRNA abundance and ABA accumulation rate in roots increased with water deficit in all transgenic lines, except in complemented aba2‐s1 mutants in which the ZEP gene was controlled by a constitutive promoter which does not respond to water deficit. These lines presented no change in root ABA content either with time or dehydration. The increase in ZEP mRNA abundance in roots with decreasing RWC was more pronounced in detached roots than in whole plants, suggesting a difference in mechanism. In all transgenic lines, a linear relationship was observed between predawn leaf water potential and [ABA] xylem , which could be reproduced in several experiments in the greenhouse and in the growth chamber. It is therefore possible to represent the effect of the transformation by a single parameter, thereby allowing the use of a quantitative approach to assist understanding of the behaviour of transgenic lines.
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Engineering seed dormancy by the modification of Zeaxanthin Epoxidase gene expression
Plant molecular biology, 1999Co-Authors: Anne Frey, Bruno Sotta, Corinne Audran, Elena Marin, A. Marion-pollAbstract:Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding Zeaxanthin Epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.
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Expression studies of the Zeaxanthin Epoxidase gene in nicotiana plumbaginifolia
Plant Physiology, 1998Co-Authors: Corinne Audran, Anne Frey, Bruno Sotta, Christian Meyer, Charlotte Borel, Thierry Simonneau, A. Marion-pollAbstract:Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C 40 ) via the C 15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes Zeaxanthin Epoxidase, which catalyzes the conversion of Zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leaves ABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds the ABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of Zeaxanthin Epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors.
Gerhard Sandmann - One of the best experts on this subject based on the ideXlab platform.
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Identification of genes coding for functional Zeaxanthin Epoxidases in the diatom Phaeodactylum tricornutum
Journal of plant physiology, 2016Co-Authors: Ulrike Eilers, Lars Dietzel, Jürgen Breitenbach, Claudia Büchel, Gerhard SandmannAbstract:Phaeodactylum tricornutum like other diatoms synthesizes fucoxanthin and diadinoxanthin as major carotenoid end products. The genes involved have recently been assigned for early pathway steps. Beyond β-carotene, only gene candidates for β-carotene hydroxylase, Zeaxanthin Epoxidase and Zeaxanthin de-Epoxidase have been proposed from the available genome sequence. The two latter enzymes may be involved in the two different xanthophyll cycles which operate in P. tricornutum. The function of three putative Zeaxanthin Epoxidase genes (zep) was addressed by pathway complementation in the Arabidopsis thaliana Zep mutant npq2. Genes zep2 and zep3 were able to restore Zeaxanthin epoxidation and a functional xanthophyll cycle but the corresponding enzymes exhibited different catalytic activities. Zep3 functioned as a Zeaxanthin Epoxidase whereas Zep2 exhibited a broader substrate specificity additionally converting lutein to lutein-5,6-epoxide. Although zep1 was transcribed and the protein could be identified after import into the chloroplast in A. thaliana, Zep1 was found not to be functional in Zeaxanthin epoxidation. The non-photochemical quenching kinetics of wild type A. thaliana was only restored in transformant npq2-zep3.
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Xanthophyll biosynthesis pathway in plants.
2015Co-Authors: Shu Chang, Lianxuan Shi, Teresa Capell, Gerhard Sandmann, Paul Christou, Judit Berman, Yanmin Sheng, Yingdian Wang, Changfu ZhuAbstract:Abbreviations: CYP97C, heme-containing cytochrome P450 carotene ε-ring hydroxylase; HYDB, β-carotene hydroxylase (non-heme di-iron β-carotene hydroxylase (BCH) and heme-containing cytochrome P450 β-ring hydroxylases CYP97A and CYP97B); LYCB, lycopene β-cyclase; LYCE, lycopene ε-cyclase; VDE, violaxanthin de-Epoxidase; ZEP, Zeaxanthin Epoxidase.
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Functional characterization of the Gentiana lutea Zeaxanthin Epoxidase ( GlZEP ) promoter in transgenic tomato plants
Transgenic research, 2012Co-Authors: Qingjie Yang, Dawei Yuan, Lianxuan Shi, Teresa Capell, Chao Bai, Nuan Wen, Gerhard Sandmann, Paul Christou, Changfu ZhuAbstract:The accumulation of carotenoids in plants depends critically on the spatiotemporal expression profiles of the genes encoding enzymes in the carotenogenic pathway. We cloned and characterized the Gentiana lutea Zeaxanthin Epoxidase (GlZEP) promoter to determine its role in the regulation of carotenogenesis, because the native gene is expressed at high levels in petals, which contain abundant chromoplasts. We transformed tomato (Solanum lycopersicum cv. Micro-Tom) plants with the gusA gene encoding the reporter enzyme β-glucuronidase (GUS) under the control of the GlZEP promoter, and investigated the reporter expression profile at the mRNA and protein levels. We detected high levels of gusA expression and GUS activity in chromoplast-containing flowers and fruits, but minimal levels in immature fruits containing green chloroplasts, in sepals, leaves, stems and roots. GlZEP-gusA expression was strictly associated with fruit development and chromoplast differentiation, suggesting an evolutionarily-conserved link between ZEP and the differentiation of organelles that store carotenoid pigments. The impact of our results on current models for the regulation of carotenogenesis in plants is discussed.
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Ketocarotenoid formation in transgenic potato
Journal of experimental botany, 2006Co-Authors: Tanja Gerjets, Gerhard SandmannAbstract:Potato has been genetically engineered for the production of commercially important ketocarotenoids including astaxanthin (3,39-dihydroxy 4,49-diketo-bcarotene). To support the formation of 3-hydroxylated and 4-ketolated b-carotene, a transgenic potato line accumulating Zeaxanthin due to inactivated Zeaxanthin Epoxidase was co-transformed with the crtO b-carotene ketolase gene from the cyanobacterium Synechocystis under a constitutive promoter. Plants were generated which exhibited expression of this gene, resulting in an accumulation of echinenone, 39-hydroxyechinenone, and 4-ketoZeaxanthin in leaves, as well as 39hydroxyechinenone, 4-ketoZeaxanthin together with astaxanthin in the tuber. The amount of ketocarotenoids formed represent ~10–12% of total carotenoids in leaves and tubers. Negative effects on photosynthesis due to the presence of the ketocarotenoids in leaves could be excluded by the determination of variable fluorescence.
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cdnas for the synthesis of cyclic carotenoids in petals of gentiana lutea and their regulation during flower development
Biochimica et Biophysica Acta, 2003Co-Authors: Saburo Yamamura, Masashiro Nishihara, Hiroyuki Koiwa, Gerhard SandmannAbstract:Abstract cDNAs encoding lycopene e-cyclase, lycopene β-cyclase, β-carotene hydroxylase and Zeaxanthin Epoxidase were isolated from a Gentiana lutea petal cDNA library. The function of all cDNAs was analyzed by complementation in Escherichia coli . Transcript levels during different stages of flower development of G. lutea were determined and compared to the carotenoid composition. Expression of all genes increased by a factor of up to 2, with the exception of the lycopene e-cyclase gene. The transcript amount of the latter was strongly decreased. These results indicate that during flower development, carotenoid formation is enhanced. Moreover, metabolites are shifted away from the biosynthetic branch to lutein and are channeled into β-carotene and derivatives.
Harry Y. Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Plant lipocalins: violaxanthin de-Epoxidase and Zeaxanthin Epoxidase.
Biochimica et Biophysica Acta, 2000Co-Authors: Arleen D. Hieber, Robert C. Bugos, Harry Y. YamamotoAbstract:Abstract Violaxanthin de-Epoxidase and Zeaxanthin Epoxidase catalyze the interconversions between the carotenoids violaxanthin, antheraxanthin and Zeaxanthin in plants. These interconversions form the violaxanthin or xanthophyll cycle that protects the photosynthetic system of plants against damage by excess light. These enzymes are the first reported lipocalin proteins identified from plants and are only the second examples of lipocalin proteins with enzymatic activity. This review summarizes the discovery and characterization of these two unique lipocalin enzymes and examines the possibility of other potential plant lipocalin proteins.
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xanthophyll cycle enzymes are members of the lipocalin family the first identified from plants
Journal of Biological Chemistry, 1998Co-Authors: Robert C. Bugos, David A Hieber, Harry Y. YamamotoAbstract:Abstract Violaxanthin de-Epoxidase and Zeaxanthin Epoxidase catalyze the addition and removal of epoxide groups in carotenoids of the xanthophyll cycle in plants. The xanthophyll cycle is implicated in protecting the photosynthetic apparatus from excessive light. Two new sequences for violaxanthin de-Epoxidase from tobacco andArabidopsis are described. Although the mature proteins are well conserved, the transit peptides of these proteins are divergent, in contrast to transit peptides from other proteins targeted to the thylakoid lumen. Sequence analyses of both violaxanthin de-Epoxidase and Zeaxanthin Epoxidase establish the xanthophyll cycle enzymes as members of the lipocalin family of proteins. The lipocalin family is a diverse group of proteins that bind small hydrophobic (lipophilic) molecules and share a conserved tertiary structure of eight β-strands forming a barrel configuration. This is the first reported identification of lipocalin proteins in plants.
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Characterization of Violaxanthin De-Epoxidase
Photosynthesis: Mechanisms and Effects, 1998Co-Authors: Arleen D. Hieber, Robert C. Bugos, Harry Y. YamamotoAbstract:Violaxanthin, antheraxanthin and Zeaxanthin in thylakoids are components of a cyclical carotenoid pathway commonly referred to as the xanthophyll or violaxanthin cycle (1). Two enzymes localized in different regions of the thylakoid catalyze the pathway. The forward half of the cycle, the de-epoxidation of violaxanthin to Zeaxanthin, is catalyzed by violaxanthin de-Epoxidase (VDE) localized in the lumen (2) whereas regeneration of violaxanthin is catalyzed by Zeaxanthin Epoxidase (ZE) localized on the stromal side of the membrane (3,4). Antheraxanthin is a common intermediate in both halves of the cycle (1).
Takaya Moriguchi - One of the best experts on this subject based on the ideXlab platform.
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carotenoid accumulation in japanese apricot prunus mume siebold zucc molecular analysis of carotenogenic gene expression and ethylene regulation
Journal of Agricultural and Food Chemistry, 2007Co-Authors: Masayuki Kita, Yoshinori Ikoma, Masaya Kato, Yusuke Ban, Chikako Honda, Hideaki Yaegaki, Takaya MoriguchiAbstract:To elucidate the regulatory mechanisms of carotenogenesis in Japanese apricot (Prunus mume Siebold & Zucc.), the relationships between carotenoid accumulation and the expression of the carotenogenic genes, phytoene synthase (PmPSY-1), phytoene desaturase (PmPDS), ζ-carotene desaturase (PmZDS), lycopene β-cyclase (PmLCYb), lycopene e-cyclase (PmLCYe), β-carotene hydroxylase (PmHYb), and Zeaxanthin Epoxidase (PmZEP), were analyzed in two cultivars with different ripening traits, ‘Orihime' and ‘Nanko.' In ‘Orihime' fruits, large amounts of carotenoids accumulated on the tree, concomitant with the induction of PmPSY-1 and the downstream carotenogenic genes PmLCYb, PmHYb, and PmZEP. In ‘Nanko' fruits, carotenoids accumulated mainly after harvest, correlating with an appreciable induction of PmPSY-1 expression, but the downstream genes were not notably induced, which may explain the lower total carotenoid content in ‘Nanko' than in ‘Orihime.' In both cultivars, a decrease in PmLCYe expression and increased or c...
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Carotenoid accumulation in Japanese apricot (Prunus mume Siebold & Zucc.): molecular analysis of carotenogenic gene expression and ethylene regulation.
Journal of agricultural and food chemistry, 2007Co-Authors: Masayuki Kita, Yoshinori Ikoma, Masaya Kato, Yusuke Ban, Chikako Honda, Hideaki Yaegaki, Takaya MoriguchiAbstract:To elucidate the regulatory mechanisms of carotenogenesis in Japanese apricot (Prunus mume Siebold & Zucc.), the relationships between carotenoid accumulation and the expression of the carotenogenic genes, phytoene synthase (PmPSY-1), phytoene desaturase (PmPDS), ζ-carotene desaturase (PmZDS), lycopene β-cyclase (PmLCYb), lycopene e-cyclase (PmLCYe), β-carotene hydroxylase (PmHYb), and Zeaxanthin Epoxidase (PmZEP), were analyzed in two cultivars with different ripening traits, ‘Orihime' and ‘Nanko.' In ‘Orihime' fruits, large amounts of carotenoids accumulated on the tree, concomitant with the induction of PmPSY-1 and the downstream carotenogenic genes PmLCYb, PmHYb, and PmZEP. In ‘Nanko' fruits, carotenoids accumulated mainly after harvest, correlating with an appreciable induction of PmPSY-1 expression, but the downstream genes were not notably induced, which may explain the lower total carotenoid content in ‘Nanko' than in ‘Orihime.' In both cultivars, a decrease in PmLCYe expression and increased or c...
Corinne Audran - One of the best experts on this subject based on the ideXlab platform.
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Localisation and expression of Zeaxanthin Epoxidase mRNA in Arabidopsis in response to drought stress and during seed development
Australian Journal of Plant Physiology, 2001Co-Authors: Corinne Audran, S. Liotenberg, M. Gonneau, H. North, A. Frey, K. Tap-waksman, N. Vartanian, A. Marion-pollAbstract:Abscisic acid (ABA) is involved in seed development and plant adaptation to environmental stresses. ABA is synthesized from cleaved xanthophylls and Zeaxanthin Epoxidase (ZEP) is the enzyme responsible for the conversion of Zeaxanthin to violaxanthin. In this study, we have characterized the ABA1 gene (AtZEP) of Arabidopsis thaliana L. and show that this complements the aba1 mutant, defective in Zeaxanthin epoxidation. The molecular basis for two aba1 mutant alleles has been determined and the reduction in their AtZEP transcript levels correlates with the molecular defect identified. As AtZEP mRNA abundance was not affected in two other ABA-deficient mutants (aba2 and aba3) and in two ABA-insensitive mutants (abi1 and abi2), no feedback regulation of ABA biosynthesis seems to occur at the level of ZEP transcription. Steady state transcript levels increased in roots during rapid water stress as well as progressive drought stress, providing evidence that Zeaxanthin epoxidation contributed to the regulation of ABA biosynthesis in roots and consequently to the plant adaptive response to hydric stress. In seeds in situ hybridization analysis detected AtZEP mRNA in the embryo cells from the globular stage to desiccation phase. In contrast, expression of AtZEP in maternal tissues was specific to the maturation phase. These results are discussed in relation to the role of ABA both in response to drought stress and in seed development.
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N. plumbaginifolia Zeaxanthin Epoxidase transgenic lines have unaltered baseline ABA acuumulations in roots and xylem sap, but contrasting sensitivities of ABA accumulation to water deficit
Journal of Experimental Botany, 2001Co-Authors: C. Borel, A. Marion-poll, Corinne Audran, A. Frey, Francois Tardieu, Thierry SimonneauAbstract:A series of transgenic lines of Nicotiana plumbaginifolia with modified expression of Zeaxanthin Epoxidase gene ( ZEP ) provided contrasting ABA accumulation in roots and xylem sap. For mild water stress, concentration of ABA in the xylem sap ([ABA] xylem ) was clearly lower in plants underexpressing ZEP mRNA (complemented mutants and antisense transgenic lines) than in wild‐type. In well‐watered conditions, all lines presented similar [ABA] xylem and similar ABA accumulation rates in detached roots. Plants could, therefore, be grown under normal light intensities and evaporative demand. Both ZEP mRNA abundance and ABA accumulation rate in roots increased with water deficit in all transgenic lines, except in complemented aba2‐s1 mutants in which the ZEP gene was controlled by a constitutive promoter which does not respond to water deficit. These lines presented no change in root ABA content either with time or dehydration. The increase in ZEP mRNA abundance in roots with decreasing RWC was more pronounced in detached roots than in whole plants, suggesting a difference in mechanism. In all transgenic lines, a linear relationship was observed between predawn leaf water potential and [ABA] xylem , which could be reproduced in several experiments in the greenhouse and in the growth chamber. It is therefore possible to represent the effect of the transformation by a single parameter, thereby allowing the use of a quantitative approach to assist understanding of the behaviour of transgenic lines.
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Engineering seed dormancy by the modification of Zeaxanthin Epoxidase gene expression
Plant molecular biology, 1999Co-Authors: Anne Frey, Bruno Sotta, Corinne Audran, Elena Marin, A. Marion-pollAbstract:Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding Zeaxanthin Epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.
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Expression studies of the Zeaxanthin Epoxidase gene in nicotiana plumbaginifolia
Plant Physiology, 1998Co-Authors: Corinne Audran, Anne Frey, Bruno Sotta, Christian Meyer, Charlotte Borel, Thierry Simonneau, A. Marion-pollAbstract:Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C 40 ) via the C 15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes Zeaxanthin Epoxidase, which catalyzes the conversion of Zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leaves ABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds the ABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of Zeaxanthin Epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors.
