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PubMed2003

Functional characterisation of two cytochrome b5-fusion desaturases from Anemone leveillei: the unexpected identification of a fatty acid Delta6-desaturase.

The Ranunculaceae are known to accumulate a wide range of unusual fatty acids in their seed lipids, and this variability has been advocated as a taxonomic marker. The Anemone species, Anemone leveillei L. and Anemone rivularis Buch.-Ham., have previously been reported to accumulate Delta5-desaturated fatty acids in their seed tissue [K. Aitzetmüller (1995) Plant Syst Evol 9:229-240]. Two cDNAs, AL1 and AL2, with similarity to plant cytochrome b5-fusion "front-end" desaturases were isolated from developing seeds of A. leveillei and their function identified by expression in Saccharomyces cerevisiae. AL2 was characterised as a sphingolipid long-chain-base Delta8-desaturase, while AL1 acted as a fatty acid desaturase. However, AL1 did not produce Delta5-desaturated fatty acids as expected; instead, when expressed in transgenic S. cerevisiae or Arabidopsis thaliana this enzyme was functionally characterised as a Delta6-desaturase. Northern analysis confirmed the expression of this gene in seed tissue and leaf tissue of A. leveillei, though Delta6-desaturated fatty acids were found to accumulate only in the leaf tissue. The unexpected characterisation of a Delta6-desaturase in A. leveillei has implications for the use of fatty acids in chemotaxonomic studies. This is also the first report of a higher-plant Delta6-desaturase from a family other than the Boraginaceae.

Amino Acid Sequence↗
PubMed2005

Senescence is accelerated, and several proteases are induced by carbon "feast" conditions in barley (Hordeum vulgare L.) leaves.

Leaf senescence is characterized by nitrogen remobilization to developing seeds of annual plants, or surviving organs of perennial species. It has been demonstrated that high carbohydrate levels (carbon "feast") are associated with the onset of the senescence process. Therefore, the development of model systems allowing the manipulation of leaf carbohydrates constitutes a logical first step in the investigation of processes important during early phases of senescence, such as plastidial protein degradation. In this study, sugar accumulation was induced either by the incubation of excised, mature barley (Hordeum vulgare L.) leaves under relatively strong light, or by the interruption of sieve tubes at the base of the leaf lamina by "steam-girdling". Accelerated chlorophyll degradation and net proteolysis confirmed successful senescence induction in both model systems, but suggested that girdled leaves are more useful than excised leaves to study proteolysis. Activities or transcript levels of several proteolytic enzymes, including plastidial (aminopeptidases, Clp protease), cytosolic (proteasome) and vacuolar (thiol proteases, an aspartic protease and a serine carboxypeptidase) proteases were clearly induced under these conditions; some of these genes also reacted to other stimuli such as leaf excision. The most interesting finding was the specific induction of a carboxypeptidase gene (cp-mIII) in girdled leaves accumulating high carbohydrate levels. As a previous study from our laboratory, using a genetic approach, has indicated that one or several carboxypeptidases are involved in leaf N remobilization, the detailed characterization of cp-mIII (and, possibly, closely related genes) may considerably improve our understanding of whole-plant N recycling.

Blotting, Northern↗
PubMed1999

Molecular analysis of a null mutant for pea (Pisum sativum L.) seed lipoxygenase-2.

A mutant line of Pisum fulvum was identified that lacked seed lipoxygenase-2 (LOX-2). The mutant phenotype was introgressed into a standard Pisum sativum cv. Birte to provide near-isogenic lines with or without seed LOX-2. Genetic analyses showed the mutation to behave as a single, recessive Mendelian gene. Northern and dot-blot analyses showed a large reduction in LOX-2 mRNA from developing seeds of the LOX-2-null mutant. A restriction fragment length polymorphism associated with the 5' end of the LOX-2 gene(s) co-segregated with the null phenotype, indicating that the reduction of LOX-2 mRNA was neither a consequence of deletion of the LOX genes nor a consequence of the action of a genetically distant regulatory gene. Analysis of the 5'-flanking sequences of LOX-2 genes from Birte and the near-isogenic LOX-2-null mutant revealed a number of insertions, deletions and substitutions within the promoter from the LOX-2-null mutant that could be responsible for the null phenotype. Incubation of crude seed LOX preparations from Birte and the LOX-2-null mutant showed that the latter generated relatively less 13-hydroperoxides and also produced relatively more hydroxy- and ketoacid compounds that have implications for the fresh-frozen pea industry.

Base Sequence↗
PubMed2000

Retention and changes of soy isoflavones and carotenoids in immature soybean seeds (Edamame) during processing.

Isoflavones and carotenoids in four experimental genotypes and Hutcheson cultivar soybeans were evaluated as a function of processing treatments and maturity. Total isoflavone and carotenoid contents were affected by genotypes and maturity stages (p < 0.0001). Total isoflavones ranged from 472 microg/g (in NTCPR93-40) to 2280 microg/g (in Hutcheson). Lutein contents ranged from 895 (in NTCPR93-286) to 2119 (in Honey Brown), and beta-carotene ranged from 291 (in Hutcheson) to 491 (in NICPR92-40) microg/100 g. Mean total isoflavone retention percentages in immature Hutcheson soybeans were 46% (boiling), 53% (freezing), and 40% (freeze-drying). Mean retentions of lutein and beta-carotene, respectively, were 92 and 73% in frozen, 62 and 62% in boiled, and 34 and 27% in freeze-dried soybeans. Boiling caused a substantial increase in daidzin, genistin, and genistein. The results show that post-harvest changes in total isoflavones and carotenoids in soybeans are influenced by processing methods, but genotype has an effect on isoflavone and carotenoid profiles during seed development.

Carotenoids↗
PubMed1996

Vicilin and Napin Storage-Protein Gene Promoters Are Responsive to Abscisic Acid in Developing Transgenic Tobacco Seed but Lose Sensitivity following Premature Desiccation.

In transgenic tobacco (Nicotiana tabacum L.) seed, expression of chimeric [beta]-glucuronidase (GUS) genes containing the vicilin or napin storage-protein gene promoters is responsive to premature drying and declines upon rehydration (L. Jiang, W.L. Downing, C.L. Baszczynski, A.R. Kermode [1995] Plant Physiol 107: 1439-1449). Desiccation may cause changes in the content of or sensitivity to abscisic acid (ABA), partially or wholly removing the effects of this "modulator" of developmental gene expression. We studied the enhancement of GUS reporter enzyme activities in transgenic tobacco by exogenous ABA before and after drying. A racemic mixture of ABA at 10 [mu]M caused a 2- to 3-fold increase in GUS activity in developing transgenic seed expressing chimeric genes containing the vicilin or napin gene promoters. However, when these seeds were prematurely dried prior to their culture on ABA medium, enhancement of GUS activity was virtually abolished. Use of optically pure ABAs revealed that the enhancement in GUS activity in developing fresh seed was due largely to the natural (+) form of ABA. Chimeric constructs containing a viral 35S promoter did not respond to ABA whether or not premature drying was applied. Thus, vicilin and napin chimeric genes, initially sensitive to ABA, become relatively insensitive to the hormone following drying. A decline in ABA sensitivity may be an important factor in the cessation of storage-protein gene expression.

Journal Article↗
PubMed2001

Characterization of a soybean

Kunitz trypsin inhibitor, an abundant soybean [Glycine max (L.) Merr.] seed protein, has a molecular mass of 21500 Da and is specific for serine proteases. A soybean mutant (P.I. 196168) was characterized to determine the molecular basis for reduced Kunitz trypsin inhibitor levels during seed development. Western blot analysis revealed that P.I. 196168, in comparison to Amsoy 71, accumulated low amounts of Kunitz trypsin inhibitor protein. Non-denaturing polyacrylamide enzyme activity gels indicated that Amsoy 71 seeds contained at least five distinct zones of trypsin inhibitor activity. However, P.I. 196168 contained only four zones of enzyme inhibition. The coding region of the most abundant trypsin inhibitor gene (KTi3) was isolated from Amsoy 71 and P.I. 196168 by PCR. DNA sequence comparisons of the Kunitz trypsin inhibitor coding regions revealed two deletions and one G to T transversion have occurred. These mutations introduced four stop codons in the reading frame, resulting in a truncated protein. Northern blot analysis revealed that P.I. 196168 accumulated drastically lower amounts of KTi3 mRNA when compared with Amsoy 71.

Journal Article↗
PubMed2000

Formation of conjugated delta8,delta10-double bonds by delta12-oleic-acid desaturase-related enzymes: biosynthetic origin of calendic acid.

Divergent forms of the plant Delta(12)-oleic-acid desaturase (FAD2) have previously been shown to catalyze the formation of acetylenic bonds, epoxy groups, and conjugated Delta(11),Delta(13)-double bonds by modification of an existing Delta(12)-double bond in C(18) fatty acids. Here, we report a class of FAD2-related enzymes that modifies a Delta(9)-double bond to produce the conjugated trans-Delta(8),trans-Delta(10)-double bonds found in calendic acid (18:3Delta(8trans,10trans,12cis)), the major component of the seed oil of Calendula officinalis. Using an expressed sequence tag approach, cDNAs for two closely related FAD2-like enzymes, designated CoFADX-1 and CoFADX-2, were identified from a C. officinalis developing seed cDNA library. The deduced amino acid sequences of these polypeptides share 40-50% identity with those of other FAD2 and FAD2-related enzymes. Expression of either CoFADX-1 or CoFADX-2 in somatic soybean embryos resulted in the production of calendic acid. In embryos expressing CoFADX-2, calendic acid accumulated to as high as 22% (w/w) of the total fatty acids. In addition, expression of CoFADX-1 and CoFADX-2 in Saccharomyces cerevisiae was accompanied by calendic acid accumulation when induced cells were supplied exogenous linoleic acid (18:2Delta(9cis,12cis)). These results are thus consistent with a route of calendic acid synthesis involving modification of the Delta(9)-double bond of linoleic acid. Regiospecificity for Delta(9)-double bonds is unprecedented among FAD2-related enzymes and further expands the functional diversity found in this family of enzymes.

Amino Acid Sequence↗
PubMed2005

Genetic analysis of two Arabidopsis DNA polymerase epsilon subunits during early embryogenesis.

Accurate DNA replication is one of the most important events in the life of a cell. To perform this task, the cell utilizes several DNA polymerase complexes. We investigated the role of DNA polymerase epsilon during gametophyte and seed development using forward and reverse genetic approaches. In Arabidopsis, the catalytic subunit of this complex is encoded by two genes, AtPOL2a and AtPOL2b, whereas the second largest regulatory subunit AtDPB2 is present as a unique complete copy. Disruption of AtPOL2a or AtDPB2 resulted in a sporophytic embryo-defective phenotype, whilst mutations in AtPOL2b produced no visible effects. Loss of AtDPB2 function resulted in a severe reduction in nuclear divisions, both in the embryo and in the endosperm. Mutations in AtPOL2a allowed several rounds of mitosis to proceed, often with aberrant planes of division. Moreover, AtDPB2 was not expressed during development of the female gametophyte, which requires three post-meiotic nuclear divisions. Since a consensus binding site for E2F transcription factors was identified in the promoter region of both genes, the promoter-reporter fusion technique was used to show that luciferase activity was increased at specific phases of the cell cycle in synchronized tobacco BY-2 cells. Our results support the idea that fertilization may utilize the mechanisms of cell cycle transcriptional regulation of genes to reactivate the divisions of the oosphere and central cell.

Arabidopsis↗
PubMed1978

Labelling of glycerolipids in the cotyledons of developing oilseeds by [1-14C] acetate and [2-3H] glycerol.

1. 3-sn-Phosphatidylcholine was identified as the major lipid in cotyledons from the developing seeds of soya bean, linseed and safflower when tissue was steamed before lipid extraction. The proportion of oleate in this lipid decreased markedly and that of the polyunsaturated C(18) fatty acids increased when detached developing cotyledons were incubated for up to 3h. Similar but less pronounced changes occurred in diacylglycerol, which had a fatty acid composition resembling that of the 3-sn-phosphatidylcholine from cotyledons of the same species. 2. [1-(14)C]Acetate supplied to detached cotyledons was incorporated into the acyl moieties of mainly 3-sn-phosphatidylcholine, 1,2-diacylglycerol and triacylglycerol. Initially label was predominantly in oleate, but subsequently entered at accelerating rates the linoleoyl moieties of the above lipids in soya-bean and safflower cotyledons and the linoleoyl and linolenyl moieties of these lipids in linseed cotyledons. In pulse-chase experiments label was rapidly lost from the oleate of 3-sn-phosphatidylcholine and accumulated in the linoleoyl and linolenoyl moieties of this phospholipid and of the di- and tri-acylglycerols. 3. [2-(3)H]Glycerol was incorporated into the glycerol moieties of mainly 3-sn-phosphatidylcholine and di- and tri-acylglycerols of developing linseed and soya-bean cotyledons. The label entered the phospholipid and diacylglycerol at rates essentially linear with time from the moment the substrate was supplied, and entered the triacylglycerol at an accelerating rate. With linseed cotyledons the labelled glycerol was incorporated initially mainly into species of 3-sn-phosphatidylcholine and diacylglycerol that contained oleate, but accumulated with time in more highly unsaturated species. In pulse-chase experiments with linseed cotyledons, label was lost from both 3-sn-phosphatidylcholine and diacylglycerol, preferentially from the dioleoyl species, and accumulated in triacylglycerol, mainly in species containing two molecules of linolenate. 4. The results suggest a rapid turnover of 3-sn-phosphatidylcholine during triacylglycerol accumulation in developing oilseeds, and are consistent with the operation of a biosynthetic route whereby oleate initially esterified to the phospholipid is first desaturated, then polyunsaturated fatty acids transferred to triacylglycerol, via diacylglycerol. The possible role of oleoyl phosphatidylcholine as a substrate for oleate desaturation is discussed.

Acetates↗
PubMed2005

Proteomic analysis of rice embryo: an approach for investigating Galpha protein-regulated proteins.

The rice dwarf1 (d1) mutant, which lacks the alpha subunit of a heterotrimeric G protein (Galpha protein), shows abnormal morphology due to shortened internodes, dark green leaves and grains that are small and round. Proteome analysis was used in this study to aid in determining the function of Galpha protein in rice embryos. Using 2-DE, seven seed embryo proteins were shown to be down-regulated in the d1 mutant as compared with its wild type. These seven proteins included a receptor for activated C-kinase (RACK) and six rice embryo globulin-2 proteins (REG2). The six REG2 have similar molecular masses with minor differences in pI. In addition to the reduced accumulation of RACK in the d1 mutant, the increase in QL/d1, in which a constitutively active form of the Galpha protein is expressed, was significantly higher as compared with wild type. The level of accumulation of these seven proteins during seed development and maturation did not change significantly until the 2nd wk after pollination. Reduced accumulation of these seven proteins started in the d1 mutant at the 3rd wk after pollination, and continued until seed maturation was complete. All seven proteins were completely absent 24 h after imbibition in both d1 mutant and its wild type. However, the phytohormone abscisic acid promoted the expression level of RACK after imbibition in the wild type as compared with d1 mutant. These results suggest that RACK is regulated by Galpha-protein and plays an important role in a basic cellular process as well as in rice embryogenesis and germination.

Down-Regulation↗
PubMed1988

Differential expression of a gene for a methionine-rich storage protein in maize.

A methionine-rich 10 kDa zein storage protein from maize was isolated and the sequence of the N-terminal 30 amino acids was determined. Based on the amino acid sequence, two mixed oligonucleotides were synthesized and used to probe a maize endosperm cDNA library. A full-length cDNA clone encoding the 10 kDa zein was isolated by this procedure. The nucleotide sequence of the cDNA clone predicts a polypeptide of 129 amino acids, preceded by a signal peptide of 21 amino acids. The predicted polypeptide is unique in its extremely high content of methionine (22.5%). The maize inbred line BSSS-53, which has increased seed methionine due to overproduction of this protein, was compared to W23, a standard inbred line. Northern blot analysis showed that the relative RNA levels for the 10 kDa zein were enhanced in developing seeds of BSSS-53, providing a molecular basis for the overproduction of the protein. Southern blot analysis indicated that there are one or two 10 kDa zein genes in the maize genome.

Amino Acid Sequence↗
PubMed2004

Expression of a Stokesia laevis epoxygenase gene.

Epoxy fatty acids have a number of important uses and there is interest in enzymes catalyzing their synthesis from renewable sources. Both cytochrome P450 monooxygenases and divergent forms of di-iron desaturases are known to produce epoxy fatty acids in plants. Degenerate primers based on conserved sequences of delta12 desaturase-like genes led to the isolation of an epoxygenase gene from Stokesia laevis. The cDNA is 1.4 kb and it encodes 378 amino acids. The similarities of this gene at the amino acid sequence level with epoxygenases of Vernonia and Crepis, and the delta12 desaturases of soybean, FAD2-1 and FAD2-2, are 84%, 69%, 49%, and 55%, respectively. When the vector, pYES2, was used to transform yeast, epoxy fatty acid formation was observed in the cells. The effects of electron donors in the yeast expression system were tested but cytochrome b5 and cytochrome b5 reductase genes from Arabidopsis thaliana co-expressed with the epoxygenase had little effect on vernolic acid accumulation in the yeast. Finally, this gene, driven by a seed-specific phaseolin promoter, was cloned into a TDNA-vector and transferred into Arabidopsis plants. The results showed that T2 seeds of transgenic Arabidopsis expressing the Stokesia gene accumulated vernolic acid but no vernolic acid was detected in control plants. Northern blot analysis indicates this S. laevis epoxygenase gene is expressed mainly in developing seeds and no transcript was detected in leaves or roots.

Asteraceae↗
PubMed2004

Analysis of an activated ABI5 allele using a new selection method for transgenic Arabidopsis seeds.

The Arabidopsis abscisic acid (ABA) insensitive (ABI)5 transcription factor participates in the ABA-dependent induction of late embryogenesis abundant (LEA) genes in the final stages of seed development. We tested whether the VP16 transcriptional activation domain is sufficient to provide ABI5 with the ability to activate the AtEm LEA genes in vegetative tissues. We took advantage of a new transgenic seed selection assay based on green fluorescent protein (GFP) fluorescence and found that VP16-ABI5 triggered growth retardation and ABA-independent induction of AtEm1 in seedlings. These results indicate that ABI5 activation potential is a limiting step and might be a target for ABA signaling.

Alleles↗
PubMed1997

Regulated expression of a wheat germin gene in tobacco: oxalate oxidase activity and apoplastic localization of the heterologous protein.

Wheat (Triticum aestivum) germin is a homopentameric glycoprotein whose synthesis is allied with seed germination. Germin pentamers show an unusual resistance to dissociation and possess an oxalate oxidase (OxO) activity. In order to increase our knowledge of germin gene expression, the function(s) of germin during development and possible uses in plant genetic engineering, an in vivo expression system is required. To this end, a gene for germin, named gf-2.8, was studied by expressing either promoter-GUS fusions or the intact gene in transgenic tobacco (Nicotiana tabacum) plants. Heterologous gene transcription was monitored in vitro and in vivo by GUS or OxO activity and was found to occur in developing seeds and in seedlings. This transcription was stimulated by auxins, as would be expected because of the presence of putative auxin-responsive elements in the promoter of the gf-2.8 gene. Auxin stimulation also extended to young leaves since OxO activity could be detected in treated but not in untreated leaves. The biochemical characteristics of wheat germin were also conserved in a transgenic host: the OxO activity was present under the form of a doublet co-migrating with germin G and G' isoforms. Also, germin distributed between a soluble and an apoplastic fractions despite the fact that wheat cell wall substantially differs from tobacco cell wall. Therefore, tobacco constitutes a suitable host for in vivo studies of this monocotyledon gene.

Amino Acid Sequence↗
PubMed2005

Divergent mating systems and parental conflict as a barrier to hybridization in flowering plants.

Parental conflicts can lead to antagonistic coevolution of the sexes and of parental genomes. Within a population, the resulting antagonistic effects should balance, but crosses between populations can reveal conflict. Parental conflict is less intense in self-pollinating plants than in outcrossers because outcrossing plants are pollinated by multiple pollen donors unrelated to the seed parent, while a self-pollinating plant is primarily pollinated by one individual (itself). Therefore, in crosses between plants with differing mating systems, outcrossing parents are expected to "overpower" selfing parents. We call this the weak inbreeder/strong outbreeder (WISO) hypothesis. Prezygotically, such overpowering can alter pollination success, and we argue that our hypothesis explains a common pattern of unilateral incompatibility, in which pollen from self-incompatible populations fertilizes ovules of self-compatible individuals but the reciprocal cross fails. A postzygotic manifestation of overpowering is aberrant seed development due to parent-of-origin effects such as genomic imprinting. We evaluate evidence for the WISO hypothesis by reviewing published accounts of crosses between plants of different mating systems. Many, but not all, of such reports support our hypothesis. Since parental conflicts can perturb fertilization and development, such conflicts may strengthen reproductive barriers between populations, contributing to speciation.

Flowers↗
PubMed1986

Relationship between Photosynthesis and Protein Synthesis in Maize: II. Interconversions of the Photoassimilated Carbon in the Ear Leaf and in the Intermediary Organs to Synthesize the Seed Storage Proteins and Starch.

The mechanisms priming the production, the movement, and the transient and final storage of the photoassimilated carbon in the maize plant were examined at the metabolic level during the formation of the seed, with the ultimate aim to identify metabolic steps restricting grain yield and explaining the delay of formation of the reserve molecules. Under normal field conditions, we show that maize directly supplies the developing seed with the photoassimilated carbon which undergoes numerous interconversions from the ear leaf to the grain. The proteins, either in the leaf or in the seed, are primarily synthesized from incoming amino acids. Nevertheless, a secondary in situ synthesis of amino acids provides the proteins with new amino acids. The amino acids of this second set, slowly synthesized in the seed from the photosynthetic carbon skeletons, are not detected in their free form but immediately and regularly incorporated into the seed proteins, in such a way that, after 4 days of chase, the proportion of the radioactive labeling of the amino acids of the different storage protein groups corresponds to their amino acid composition. In the leaf, the labeling of proteins also arises from different metabolisms, but mainly from the photosynthetic metabolism. Contrary to the seed proteins, the time course of the labeled leaf proteins implies a rapid turnover. The second labeling of starch and proteins in the ear leaf involves a reassimilation of CO(2), a process optimizing the carbon uptake in maize.

Journal Article↗
PubMed2000

On the radioanalytical methods used to assay stainless-steel-encapsulated, ceramic-based 90Sr-90Y intravascular brachytherapy sources.

Very quantitative radiochemical procedures for the destructive assay of stainless-steel-encapsulated, ceramic-based 90Sr-90Y intravascular brachytherapy sources (termed 'seeds') have been devised. These seeds, developed and provided by Bebig Isotopentechnic und Umweltdiagnostik (Berlin, Germany) in collaboration with the Novoste Corporation (Norcross, GA), are intended for use in the prophylactic treatment of restenosis following balloon angioplasty in heart-disease patients. The procedures were applied to the radionuclidic assay of both the bare-ceramic source materials (of proprietary composition) contained within the seeds and to the stainless-steel (SS) sealed sources. The approach consisted of extracting some arbitrary fraction of the 90Sr activity from the ceramic-like material and assaying the resulting solution by 4pi beta liquid scintillation (LS) spectrometry with 3H-standard efficiency tracing. The fraction of extracted activity was determined by ionization current measurements before and after the chemical extraction. All of the ionization current and LS-based activity determinations were made under the experimentally-verified conditional that 90Y was in radioactive equilibrium with 90Sr. For the assay of the SS-jacketed seeds, the encapsulation was initially dissolved and the resultant solution was also assayed by LS spectrometry to determine the amount of activity removed by the SS dissolution step. The developed protocol included provisions for accounting for all possible losses of 90Sr activity in the chemical and source-handling procedures, for the unrecovered activity in the extracted source material and for any residual activity in the solution-transfer and source-handling tools. These destructive assays were required for relating radiochromic-fill measurements of the absorbed dose spatial distributions for the seeds to theoretic dose modelling and for establishing calibration factors for subsequent non-destructive radionuclidic measurements on the seeds.

Brachytherapy↗
PubMed1996

Molecular identification of zeaxanthin epoxidase of Nicotiana plumbaginifolia, a gene involved in abscisic acid biosynthesis and corresponding to the ABA locus of Arabidopsis thaliana.

Abscisic acid (ABA) is a plant hormone which plays an important role in seed development and dormancy and in plant response to environmental stresses. An ABA-deficient mutant of Nicotiana plumbaginifolia, aba2, was isolated by transposon tagging using the maize Activator transposon. The aba2 mutant exhibits precocious seed germination and a severe wilty phenotype. The mutant is impaired in the first step of the ABA biosynthesis pathway, the zeaxanthin epoxidation reaction. ABA2 cDNA is able to complement N.plumbaginifolia aba2 and Arabidopsis thaliana aba mutations indicating that these mutants are homologous. ABA2 cDNA encodes a chloroplast-imported protein of 72.5 kDa, sharing similarities with different mono-oxigenases and oxidases of bacterial origin and having an ADP-binding fold and an FAD-binding domain. ABA2 protein, produced in Escherichia coli, exhibits in vitro zeaxanthin epoxidase activity. This is the first report of the isolation of a gene of the ABA biosynthetic pathway. The molecular identification of ABA2 opens the possibility to study the regulation of ABA biosynthesis and its cellular location.

Abscisic Acid↗