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PubMed1994

Synthesis of trilaurin by developing pisa seeds (Actinodaphne hookeri).

The developing seeds of Actinodaphne hookeri were investigated to delineate their ability to synthesize large amounts of trilaurin. Until 88 days after flowering the embryos contained 71% neutral lipids (NL) and 29% phospholipids (PL) and both these components contained C16:0, C18:0, C18:2, and C18:3 as the major fatty acids (FA). At 102 days after flowering the seeds began to accumulate triacylglycerols (TAG) and to synthesize lauric acid (C12:0). By 165 days after flowering, when the seeds were mature, they contained about 99% NL and 1% PL. At this stage the TAG contained exclusively C12:0, while the PL consisted of long-chain fatty acids (LCFA) only. Leaf lipids in contrast did not contain any C12:0. Experiments on [1-14C]acetate incorporation into developing seed slices showed that at 88 days after flowering only 4% of the label was in TAG, 1% in diacylglycerols (DAG), and 87% in PL. One hundred two days after flowering seeds incorporated only 2% of the label into TAG, 30% into DAG, and 64% into PL. In contrast at 114 days after flowering 71% of the label was incorporated into TAG, 25% into DAG, and only 2% into PL. Analysis of labeled FA revealed that up to 102 days after flowering it was incorporated only into LCFA, whereas at 114 days after flowering it was incorporated exclusively into C12:0. Furthermore, 67% of the label in PL at 114 days after flowering was found to be dilaurylglycerophosphate. Analysis of the label in DAG at this stage showed that it was essentially in dilaurin species. These observations indicate the induction of enzymes of Kennedy pathway for the specific synthesis of trilaurin at about 114 days after flowering. Homogenates of seeds (114 days after flowering) incubated with labeled FA in the presence of glycerol-3-phosphate and coenzymes A and ATP incorporated 84% of C12:0 and 61% of C14:0, but not C16:0, C18:2, and C18:3, into TAG. In contrast the LCFA were incorporated preferentially into PL. It is concluded that, between 102 and 114 days after flowering, a switch occurs in A. hookeri for the synthesis of C12:0 and trilaurin which is tissue specific. Since the seed synthesizes exclusively C12:0 at 114 days after flowering onwards and incorporates specifically into TAG, this system appears to be ideal for identifying the enzymes responsible for medium-chain fatty acid as well as trilaurin synthesis and for exploiting them for genetic engineering.

Acetates↗
PubMed1997

The isolation of a novel metallothionein-related cDNA expressed in somatic and zygotic embryos of Douglas-fir: regulation by ABA, osmoticum, and metal ions.

To isolate genes which are expressed preferentially during embryogenesis, a Douglas-fir embryogenesis cDNA library was constructed and differentially screened with cDNA probes made with mRNA from developing and mature embryos, respectively. The cDNA clone PM 2.1 was isolated based on its abundance in developing seeds and absence in mature seeds, and its predicted amino acid sequence was shown to have structural features characteristic of plant MT-like proteins. Alignment of the PM 2.1 predicted amino acid sequence with other plant MT-like protein sequences revealed a general paucity of Cys and Cys-Xaa-Cys sequences and the presence of novel serine residues within the conserved Cys-Xaa-Cys motifs in the C-terminal domain. The consensus sequence following the Cys-poor spacer in type 2 MT-like proteins, CXCXXXCXCXXCXCX, was modified in PM 2.1 to CXSXXXSXYXX-XCX. Phylogenetic analysis supported PM 2.1 was distinct from other MT and grouped with MT-like proteins from Arabidopsis (OEST), rice (AEST) and kiwifruit (AD1), which do not belong to type 1 or 2. The PM 2.1 gene was expressed in somatic and zygotic embryos, in haploid maternal tissue, as well as in hormone- and metal-treated seeds and seedlings. The PM 2.1 transcripts were detected in the needles of 14-week-old seedlings, but not the root tissue or mature pollen. The expression of the PM 2.1 gene in embryos was dependent upon ABA and osmoticum and in seedlings was differentially modulated by metals, suggesting a role of the PM 2.1 gene product in the control of microelement availability during Douglas-fir seed development and germination. The novel structural features, and the developmental, hormonal and metal modulation of PM 2.1 expression, are evidence for a new type of MT-related protein in plants.

Abscisic Acid↗
PubMed1993

Molecular analysis of the gene encoding a rice starch branching enzyme.

The sequence of a rice gene encoding a starch branching enzyme (sbe1) shows extreme divergence from that of the rice gene, that is homologous to bacterial glycogen branching enzyme (sbe2). sbe1 is expressed abundantly and specifically in developing seeds and maximally in the middle stages of seed development. This expression pattern completely coincides with that of the waxy gene, which encodes a granule-bound starch synthase. Three G-box motifs and consensus promoter sequences are present in the 5' flanking region of sbe1. It encodes a putative transit peptide, which is required for transport into the amyloplast. A 2.2 kb intron (intron 2) precedes the border between the regions encoding the transit peptide and the mature protein, and contains a high G/C content with several repeated sequences in its 5' half. Although only a single copy of sbe1 is present in the rice genome, Southern analysis using intron 2 as a probe indicates the presence of several homologous sequences in the rice genome, suggesting that this large intron and also the transit peptide coding region may be acquired from another portion of the genome by duplication and insertion of the sequence into the gene.

1,4-alpha-Glucan Branching Enzyme↗
PubMed2005

Barley Dhn13 encodes a KS-type dehydrin with constitutive and stress responsive expression.

Dehydrins (DHNs) compose a family of intrinsically unstructured proteins that have high water solubility and accumulate during late seed development, low temperature or water deficit conditions, and are thought to play a protective role in freezing and drought tolerance in plants. Twelve Dhn genes were previously described in the barley genome. Here, we report an additional member of this multigene family, Dhn13. The Dhn13 gene is located in chromosome 4 near marker MWG634 and encodes a 107-amino acid KS-type DHN. Semi-quantitative reverse transcriptase PCR data indicated that Dhn13 is constitutively expressed in seedling tissues and embryos of developing seeds. Microarray data were consistent with these results and showed a considerable increase of Dhn13 transcripts when plants were subjected to chilling and freezing temperatures. The highest transcript levels where observed in anthers. The presence of ABRE, MYC, DRE, and POLLEN1LELAT52 regulatory elements in the putative Dhn13 promoter region is in agreement with expression data.

Amino Acid Sequence↗
PubMed2002

What limits production of unusual monoenoic fatty acids in transgenic plants?

Unusual monounsaturated fatty acids are major constituents (greater than 80%) in seeds of Coriandrum sativum L. (coriander) and Thunbergia alata Bojer, as well as in glandular trichomes (greater than 80% derived products) of Pelargonium x hortorum (geranium). These diverged fatty acid structures are produced via distinct plastidial acyl-acyl carrier protein (ACP) desaturases. When expressed in Arabidopsis thaliana (L.) Heynh. under strong seed-specific promoters the unusual acyl-ACP desaturases resulted in accumulation of unusual monoene fatty acids at 1-15% of seed fatty acid mass. In this study, we have examined several factors that potentially limit higher production of unusual monoenes in transgenic oilseeds. (i) Immunoblots indicated that the introduced desaturases were expressed at levels equivalent to or higher than the endogenous delta9 18:0-ACP desaturase. However, the level of unusual fatty acid produced in transgenic plants was not correlated with the level of desaturase expression. (ii) The unusual desaturases were expressed in several backgrounds, including antisense 18:0-ACP desaturase plants, in fab1 mutants, and co-expressed with specialized ACP or ferredoxin isoforms. None of these experiments led to high production of expected products. (iii) No evidence was found for degradation of the unusual fatty acids during seed development. (iv) Petroselinic acid added to developing seeds was incorporated into triacylglycerol as readily as oleic acid, suggesting no major barriers to its metabolism by enzymes of glycerolipid assembly. (v) In vitro and in situ assay of acyl-ACP desaturases revealed a large discrepancy of activity when comparing unusual acyl-ACP desaturases with the endogenous delta9 18:0-ACP desaturase. The combined results, coupled with the sensitivity of acyl-ACP desaturase activity to centrifugation and low salt or detergent suggests low production of unusual monoenes in transgenic plants may be due to the lack of, or incorrect assemble of, a necessary multi-component enzyme association.

Acanthaceae↗
PubMed2002

Differential characteristics and subcellular localization of two starch-branching enzyme isoforms encoded by a single gene in Phaseolus vulgaris L.

Starch-branching enzymes (SBE) have a dominant role for amylopectin structure as they define chain length and frequency of branch points. We have previously shown that one of the SBE isoforms of kidney bean (Phaseolus vulgaris L.), designated PvSBE2, has a molecular mass (82 kDa) significantly smaller than those reported for isologous SBEs from pea (SBEI), maize (BEIIb), and rice (RBE3). Additionally, in contrast to the dual location of the pea SBEI in both the soluble and starch granule fractions, PvSBE2 was found only in the soluble fraction during seed development. Analysis of a pvsbe2 cDNA suggested that PvSBE2 is generated from a larger precursor with a putative plastid targeting sequence of 156 residues. Here we describe the occurrence of a larger 100-kDa form (LF-PvSBE2) of PvSBE2 found both in the soluble and starch granule fractions of the developing seeds. The determined N-terminal sequence, VKSSHDSD, of LF-PvSBE2 corresponded to a peptide sequence located 111 amino acids upstream from the N terminus of purified PvSBE2, suggesting that LF-PvSBE2 and PvSBE2 are products of the same gene. Analysis of the products by 5'-RACE (rapid amplification of cDNA ends) and reverse transcription PCR indicated that the two transcripts for pre-LF-PvSBE2 and pre-PvSBE2 are generated by alternative splicing. Recombinant LF-PvSBE2 (rLF-PvSBE2) was purified from Escherichia coli and the kinetic properties were compared with those of recombinant PvSBE2 (rPvSBE2). rLF-PvSBE2 had much higher affinity for amylopectin (K(m) = 4.4 mg/ml) than rPvSBE2 (18.4 mg/ml), whereas the V(max) of rLF-PvSBE2 (135 units/mg) for this substrate was much lower than that of rPvSBE2 (561 units/mg). These results suggest that the N-terminal extension of LF-PvSBE2 plays a critical role for localization in starch granules by altering its enzymatic properties.

1,4-alpha-Glucan Branching Enzyme↗
PubMed2006

Spatial and temporal expression of the response regulators ARR22 and ARR24 in Arabidopsis thaliana.

ARR22 (At3g04280) is a novel Type A response regulator whose function in Arabidopsis is unknown. RT-PCR analysis has shown that expression of the gene takes place in flowers and developing pods with the tissues accumulating different proportions of splice variants. Spatial analysis of expression, using ARR22::GUS plants as a marker, has revealed that the reporter protein accumulates specifically at the junction between the funiculus and the chalazal tissue. Expression can be up-regulated at this location by wounding the developing seed. A detailed analysis has failed to detect ARR22 expression at any other sites and, to support this assertion, the only evidence for tissue ablation in ARR22::Barnase plants is during seed development, with the consequence that embryo growth is attenuated. Ectopic expression of ARR22, driven by either the CaMV 35S or the pea plastocyanin (PPC) promoters, resulted in the generation of plants exhibiting extremely stunted root and shoot growth. No viable progeny could be isolated from the PPC::ARR22 transgenic lines. An RT-PCR analysis of a recently annotated gene (ARR24-At5g26594), that exhibits 66% amino acid similarity to ARR22, has shown that expression is also predominantly in floral and silique tissues. Examination of ARR24::GUS plants has revealed that the activity of the promoter is primarily restricted to pollen grains indicating that this gene is unlikely to display an overlapping function with ARR22. Analyses of individual KO lines of either ARR22 or ARR24 have failed to identify a mutant phenotype under the growth conditions employed and the double knockout ARR22/ARR24 line is also indistinguishable from wild-type plants. These results are discussed in the light of the proposed role of response regulators in plant growth and development.

Arabidopsis↗
PubMed1999

Differentially and developmentally regulated expression of three rice sucrose synthase genes.

The spatial and temporal distribution of sucrose synthase (RSuS) in rice (Oryza sativa L.) was studied by Western and immunohistochemical analyses using the monospecific antibodies for three RSuS isoforms. In leaf tissues, RSuS1 was localized in the mesophyll while RSuS2 was in the phloem in addition to the mesophyll. In the roots, only RSuS1 was found in the phloem. No RSuS3 could be detected in any parts of etiolated seedlings. The expression of each RSus gene is closely linked to the seed development. RSuS1 was present in the aleurone layers of developing seeds, and at a low level in endosperm cells. RSuS2 was evenly distributed in seed tissues other than the endosperm. RSuS3 was localized predominantly in the endosperm cells. The tissue specific localizations of the three gene products suggest that RSuS1 plays a role in sugar transport into endosperm cells where the reaction catalyzed by RSuS3 provides the precursor of starch synthesis. RSus2, which is ubiquitously expressed, may play a housekeeping role.

Amino Acid Sequence↗
PubMed2005

Contribution of gibberellins to the formation of Arabidopsis seed coat through starch degradation.

To clarify the role of gibberellins in the seed development of Arabidopsis, we investigated the sites where gibberellins are synthesized and induce alpha-amylase genes. The spatial and temporal expression of the genes encoding gibberellin biosynthetic enzymes and alpha-amylases was examined by reverse transcription-PCR (RT-PCR) and in situ hybridization. The mRNAs of AtGA20ox2, AtGA20ox3 and AtGA3ox4 began to be detectable 5-7 d after pollination. In situ hybridization showed that these genes were expressed almost simultaneously around starch granules in the outer integument, preceding the disappearance of those granules. AtGA20ox2 and AtGA3ox4 but not AtGA20ox3 also showed their signals at the rim of the developing embryo. The alpha-amylase gene, Amy3, which responded to gibberellin, was mainly expressed in the developing seed, spatially overlapping with the expression of AtGA20ox2 and AtGA3ox4. These results suggest that gibberellins function in at least two sites of the seed: the outer integument and part of the embryo. We examined the phenotypes of a T-DNA insertion line of AtGA3ox4 and observed the following: (i) a decrease of alpha-amylase gene transcripts in young siliques; (ii) delay of starch degradation in the outer integument; (iii) disarrangement of the seed surface structure; and (iv) abnormal swelling pattern of polysaccharides after imbibition by the mature seed. These characteristics are phenotypes of plants under gibberellin starvation, because the abnormalities could be almost overcome with applied gibberellin, and the gibberellin-treated mutant was indistinguishable from the wild type. These results strongly suggest that gibberellins in the outer integument would be required for the normal formation of the Arabidopsis seed coat.

Arabidopsis↗
PubMed1985

Correct targeting of the bean storage protein phaseolin in the seeds of transformed tobacco.

The storage protein phaseolin accumulates during seed development in protein bodies in cotyledons of the common bean Phaseolus vulgaris. Hall et al. (In L Van Vloten-Doting, TC Hall, eds, Molecular Form and Function of the Plant Genome, 1985 Plenum Press, In press) recently reported the expression of a gene coding for phaseolin and the accumulation of phaseolin protein in developing seeds of tobacco plants regenerated from transformed callus cells. The protein did not accumulate in other organs of the plants. Mature seeds from normal and transformed tobacco plants were obtained and the subcellular distribution of phaseolin in the seeds was examined using both light and electron microscopic immunocytochemical methods. Phaseolin was found in six of seven transformed tobacco embryos examined, but was present in only one endosperm of five. When present, phaseolin was located exclusively in the protein bodies of the embryonic and endospermic cells. Furthermore, phaseolin was restricted solely to the amorphous matrix of the protein bodies and was excluded from the globoid and proteinaceous crystalloid components of these organelles. The subcellular location of phaseolin in seeds from transformed tobacco plants is similar to that seen in mature seeds of the common bean indicating that in the transformed cells the protein is targeted to the right subcellular compartment.

Journal Article↗
PubMed1986

Distribution and Metabolism of sym-Homospermidine and Canavalmine in the Sword Bean Canavalia gladiata cv Shironata.

The unusual polyamines, sym-homospermidine (homoSPD) and canavalmine (CAN), were found in the seed of Canavalia species such as C. gladiata, C. ensiformis, and C. brasilensis, but not in those of other leguminous crops. To examine the distribution and metabolism of homoSPD and CAN in sword bean, C. gladiata cv Shironata, polyamine analysis was carried out throughout the life cycle of this plant. During seed germination, putrescine (PUT), spermidine (SPD), and spermine (SPM) were accumulated in the radicle and hypocotyl. HomoSPD and CAN were, however, maintained at very low levels over a 6-day period of germination. In nodulated sword bean plants, a large quantity of homoSPD was found in the root nodule. CAN was detected exclusively in the senescent nodule at very low concentrations. These polyamines were not detected in any other organs including root, stem, leaf, vine, flower, and pod, while PUT, SPD, and SPM were always found in those organs. As plants reached the reproductive stage, homoSPD and CAN appeared in the immature seed and their concentrations increased as seed formation progressed. By contrast, the level of SPM continuously decreased during seed development. In developing seeds, considerable accumulation of canavanine, an analog of arginine, which is a precursor in polyamine biosynthesis, was also observed.

Journal Article↗
PubMed1990

Three Classes of Abscisic Acid (ABA)-Insensitive Mutations of Arabidopsis Define Genes that Control Overlapping Subsets of ABA Responses.

Wild type and three abscisic acid (ABA)-insensitive mutants of Arabidopsis (ABI1, ABI2, and ABI3) were compared for their ability to respond to ABA for a variety of ABA-inducible responses throughout the life cycle of the plants. The responses tested included effects on seedling growth, proline accumulation in seedlings, ABA-regulated protein synthesis in plantlets, and seed storage protein and lipid synthesis and accumulation. The abi1 and abi2 mutants showed reduced sensitivity to ABA for inhibition of seedling growth, induction of proline accumulation, and alterations in protein synthesis patterns during vegetative growth, but had wild type levels of storage reserves. In contrast, the abi3 mutant had wild type sensitivity for induction of proline accumulation and was only slightly less responsive to ABA with respect to effects on seedling growth and changes in patterns of protein synthesis. The major effects of this mutation were on seed development. Seeds of the abi3 mutant had two-thirds of the wild type level of storage protein and one-third the wild type level of eicosenoic acid, the major fatty acid component of storage lipids in wild type seeds. These results show that none of the abi mutants is insensitive for all ABA-inducible responses and that the abi3 effects are not seed-specific. Comparison of the degree of ABA sensitivity of monogenic mutant lines with that of digenic mutant lines carrying pairwise combinations of the abi mutations suggests that ABA responses in mature seeds are controlled by at least two parallel pathways.

Journal Article↗
PubMed1992

Expression of "Dehydrin-Like" Proteins in Embryos and Seedlings of Zizania palustris and Oryza sativa during Dehydration.

Proteins inducible by dehydration and abscisic acid (ABA), termed dehydrins or RAB (Responsive to ABA) proteins, have been identified in a number of species and have been suggested to play a role in desiccation tolerance, particularly during seed development. Seeds (caryopses) of North American wild rice (Zizania palustris var interior [Fassett] Dore) are tolerant of dehydration to <10% moisture content (fresh weight basis) only under restricted dehydration and rehydration conditions. In comparison, seeds of paddy rice (Oryza sativa L.) readily tolerate desiccation to <5% water content. Expression of "dehydrin-like" proteins in Zizania and Oryza seedlings and embryos was examined to investigate the relationship between the presence of such proteins and desiccation tolerance. [(35)S]Methionine labeling of newly synthesized proteins showed that seedlings (first leaf stage) of both Zizania and Oryza synthesized a novel "heat-stable" protein of apparent molecular weight = 20,000 when dehydrated to <75% of their initial fresh weight. ABA (100 micromolar) induced synthesis of a protein with similar electrophoretic mobility in both species. Western blots using antiserum raised against maize (Zea mays L.) dehydrin detected a protein band from dehydrated Zizania shoots and mature embryonic axes that comigrated with the labeled 20-kilodalton polypeptide. Northern blots using a cDNA for an ABA-responsive protein from Oryza (rab 16a) showed that both seedlings and excised embryonic axes of Zizania accumulated RNA similar in sequence to rab 16a in response to water loss. Zizania seedlings and embryonic axes were also capable of ABA accumulation during dehydration. The intolerance of Zizania seeds to dehydration at low temperature is apparently not due to an absence of dehydrin-like proteins or an inability to accumulate ABA.

Journal Article↗
PubMed1992

Accumulation of Group 3 Late Embryogenesis Abundant Proteins in Zea mays Embryos : Roles of Abscisic Acid and the Viviparous-1 Gene Product.

Several different types of proteins that are modulated by abscisic acid (ABA) accumulate in developing embryos of maize (Zea mays L.). Some of these proteins are specific to the developing seed, such as the storage globulin, GLB1, whereas others are involved in general responses to water deficit. Here we describe a maize protein family of this second type, a Group 3 late embryogenesis abundant (MLG3). Like other proteins of this class, MLG3 polypeptides are ABA-responsive. They are found in maturing seeds and in dehydrating plant tissues. Antigenically related proteins are found in other cereals. To distinguish the regulation of developmentally programmed ABA responses from those that are environmentally induced, we compared the ontological pattern and accumulation requirements of MLG3 polypeptides with those we previously described for GLB1. GLB1 accumulation begins early in the maturation phase and specifically requires high levels of ABA and the participation of the Viviparous-1 (Vp1) gene product. Vp1 is required for other ABA-modulated events in maize seed development as well. In experiments using vp1 mutants and mutants deficient in ABA synthesis (vp5 mutation), we show that MLG3 accumulation also is dependent upon ABA, but it shows striking differences from GLB1. MLG3 accumulates much later in embryogenesis, coincident with the onset of dehydration. In contrast to GLB1, MLG3 proteins can be induced by de novo ABA synthesis in response to culturing in high osmoticum. Unlike GLB1, MLG3 has no specific requirement for the Vp1 gene product.

Journal Article↗
PubMed1990

Expression of mutant patatin protein in transgenic tobacco plants: role of glycans and intracellular location.

The influence of N-glycosylation and subcellular compartmentation on various characteristics of a vacuolar glycoprotein is described. One member of the patatin gene family was investigated as a model system. Different glycosylation mutants obtained by destroying the consensus site Asn-X-Ser/Thr by oligonucleotide-directed mutagenesis were expressed in leaves of transgenic tobacco plants under the control of a light-inducible promoter. The various patatin glycomutants retained their properties in comparison with the wild-type protein with respect to protein stability, subcellular compartmentation, enzymatic activity, and various physicochemical properties studied showing the N-glycosylation not to be essential for any of these characteristics. To test the importance of the cotranslational transport and the subcellular (vacuolar) location for the properties of the patatin protein, another mutant was constructed in which the signal peptide was deleted, leading to its synthesis and accumulation in the cytosol. Biochemical analysis of this protein in comparison with its vacuolar form again revealed no significant differences with respect to its enzymatic activity or its stability in normal vegetative cells. During seed development, however, the cytoplasmic form was more stable than the vacuolar form, indicating the appearance of proteases specific for the protein bodies of developing seeds.

Amino Acid Sequence↗
PubMed2006

The regulatory function of the upstream sequence of the beta-conglycinin alpha subunit gene in seed-specific transcription is associated with the presence of the RY sequence.

beta-conglycinin, a major component of seed-storage proteins in soybean, comprises three subunits: alpha, alpha', and beta. Expression of these genes is spatially regulated in a stringent manner and occurs during seed development. To understand the mechanisms that control expression of the alpha subunit gene, we analyzed the nucleotide sequence of the 2.9-kb region upstream of the gene. The upstream sequence up to -1357 or a series of its 5'-deleted derivatives was fused to the beta-glucuronidase (GUS) gene. These reporter gene constructs were introduced into Arabidopsis thaliana plants via Agrobacterium-mediated gene transfer. Prominent GUS activity was detected in developing seeds of the T3 generation when 245 bp or longer sequences of the upstream region were fused to the GUS gene. We found a clear association of decreased GUS activity with a stepwise deletion of a region containing the RY sequence from the original construct. These results are consistent with the notion that multiple sequence elements including the RY sequences are involved in the seed-specific transcriptional activation of the beta-conglycinin alpha subunit gene in soybean.

Antigens, Plant↗
PubMed1994

Tissue-specific expression of an oat 12S seed globulin gene in developing tobacco seeds: differential mRNA and protein accumulation.

We studied the expression of the oat globulin gene asglo5 in developing transgenic tobacco seeds. The asglo5 gene promoter directed transcription in the endosperm as well as in the provascular tissue, the presumptive root tip and the shoot apical meristem of the embryo as revealed by GUS reporter gene constructs and in situ hybridization. However, immunological tissue printing detected the oat protein exclusively in the tobacco endosperm, suggesting that extensive post-transcriptional regulatory processes influence the expression of the monocot transgene in the dicot host.

Allergens↗
PubMed2000

Diacylglycerol acyltransferase in maturing sunflower seeds.

Developing sunflower seeds exhibit a high diacylglycerol acyltransferase (DAGAT, EC 2.3.1.20) activity. The distribution of the enzyme has been studied in subcellular fractions prepared by differential centrifugation of seed homogenate. Its activity was characterized using [1-(14)C]oleoyl-CoA and diolein dispersed in Tween 20. Some properties of the microsomal fraction of DAGAT were investigated. Hyperbolic kinetics were observed, the apparent K(m) was 60 microM and the specific activity of the reaction 15 pmol/min/mg of protein. Addition of BSA (0.1%) stimulated oleate incorporation, which was not dependent on the presence of exogenous diacylglycerol. Detergents which might solubilize DAGAT, Triton X-100 and CHAPS, were tested for enzyme inhibition, and CHAPS was found to be the least denaturing.

Acyl Coenzyme A↗