Barley aleurone cell development: molecular cloning of aleurone-specific cDNAs from immature grains

The impact of multiple abiotic stresses on ns-LTP2.8 gene transcript and ns-LTP2.8 protein accumulation in germinating barley (Hordeum vulgare L.) embryos

Abiotic stresses occur more often in combination than alone under regular field conditions limiting in more severe way crop production. Stress recognition in plants primarily occurs in the plasma membrane, modification of which is necessary to maintain homeostasis in response to it. It is known that lipid transport proteins (ns-LTPs) participate in modification of the lipidome of cell membranes. Representative of this group, ns-LTP2.8, may be involved in the reaction to abiotic stress of germinating barley plants by mediating the intracellular transport of hydrophobic particles, such as lipids, helping to maintain homeostasis. The ns-LTP2.8 protein was selected for analysis due to its ability to transport not only linear hydrophobic molecules but also compounds with a more complex spatial structure. Moreover, ns-LTP2.8 has been qualified as a member of pathogenesis-related proteins, which makes it particularly important in relation to its high allergenic potential. This paper demonstrates for the first time the influence of various abiotic stresses acting separately as well as in their combinations on the change in the ns-LTP2.8 transcript, ns-LTP2.8 protein and total soluble protein content in the embryonal axes of germinating spring barley genotypes with different ns-LTP2.8 allelic forms and stress tolerance. Tissue localization of ns-LTP2.8 transcript as well as ns-LTP2.8 protein were also examined. Although the impact of abiotic stresses on the regulation of gene transcription and translation processes remains not fully recognized, in this work we managed to demonstrate different impact on applied stresses on the fundamental cellular processes in very little studied tissue of the embryonal axis of barley.

Promoter of the wheat lipid transfer protein, TdLTP4, drives leaf-preferential expression in transgenic Arabidopsis plants

In a previous report, a gene encoding a durum wheat lipid transfer protein, TdLTP4, was characterised as induced by abiotic and biotic stresses. In the present work, we investigated the regulation of the gene TdLTP4. A TdLTP4 promoter (PrTdLTP4) region of around 868-bp was isolated and sequenced. Its analysis revealed the presence of several DNA boxes known to be important mainly in the regulation of genes expressed under abiotic stress (salt and dehydration), abscisic acid (ABA) and pathogen responsiveness. The whole PrTdLTP4 fragment was fused to the reporter gene β-glucuronidase (gusA) and analysed in transgenic Arabidopsis plants. Histochemical assays of transgenic Arabidopsis plants showed that the 868-bp fragment of TdLTP4 gene promoter was found to be sufficient for both spatial and temporal patterns of its expression. Under control conditions, GUS histochemical staining was observed significantly only in young leaves of 8- and 12-day-old plants. Whereas after stress challenge especially with NaCl and mannitol, GUS transcripts expression increased substantially in leaves of 30-day-old transgenic seedlings. Real-time qPCR expression analysis of the gusA gene, confirmed the results of histochemical assays. Taken together these data provide evidence that PrTdLTP4 functions as abiotic-stress-inducible promoter in a heterologous dicot system and could be an excellent tool for future crop improvement.

The mitochondrion-located protein OsB12D1 enhances flooding tolerance during seed germination and early seedling growth in rice

B12D belongs to a function unknown subgroup of the Balem (Barley aleurone and embryo) proteins. In our previous work on rice seed germination, we identified a B12D-like protein encoded by LOC_Os7g41350 (named OsB12D1). OsB12D1 pertains to an ancient protein family with an amino acid sequence highly conserved from moss to angiosperms. Among the six OsB12Ds, OsB12D1 is one of the major transcripts and is primarily expressed in germinating seed and root. Bioinformatics analyses indicated that OsB12D1 is an anoxic or submergence resistance-related gene. RT-PCR results showed OsB12D1 is induced remarkably in the coleoptiles or roots by flooding during seed germination and early seedling growth. The OsB12D1-overexpressed rice seeds could protrude radicles in 8 cm deep water, further exhibiting significant flooding tolerance compared to the wild type. Moreover, this tolerance was not affected by the gibberellin biosynthesis inhibitor paclobutrazol. OsB12D1 was identified in the mitochondrion by subcellular localization analysis and possibly enhances electron transport through mediating Fe and oxygen availability under flooded conditions. This work indicated that OsB12D1 is a promising gene that can help to enhance rice seedling establishment in farming practices, especially for direct seeding.

Lipid transfer proteins in coffee: isolation of Coffea orthologs, Coffea arabica homeologs, expression during coffee fruit development and promoter analysis in transgenic tobacco plants

The aim of the present study was to perform a genomic analysis of non-specific lipid-transfer proteins (nsLTPs) in coffee. Several nsLTPs-encoding cDNA and gene sequences were cloned from Coffea arabica and Coffea canephora species. In this work, their analyses revealed that coffee nsLTPs belong to Type II LTP characterized under their mature forms by a molecular weight of around 7.3 kDa, a basic isoelectric points of 8.5 and the presence of typical CXC pattern, with X being an hydrophobic residue facing towards the hydrophobic cavity. Even if several single nucleotide polymorphisms were identified in these nsLTP-coding sequences, 3D predictions showed that they do not have a significant impact on protein functions. Northern blot and RT-qPCR experiments revealed specific expression of Type II nsLTPs-encoding genes in coffee fruits, mainly during the early development of endosperm of both C. arabica and C. canephora. As part of our search for tissue-specific promoters in coffee, an nsLTP promoter region of around 1.2 kb was isolated. It contained several DNA repeats including boxes identified as essential for grain specific expression in other plants. The whole fragment, and a series of 5' deletions, were fused to the reporter gene β-glucuronidase (uidA) and analyzed in transgenic Nicotiana tabacum plants. Histochemical and fluorimetric GUS assays showed that the shorter (345 bp) and medium (827 bp) fragments of nsLTP promoter function as grain-specific promoters in transgenic tobacco plants.

Peroxiredoxin antioxidants in seed physiology

Peroxiredoxins are thiol–requiring antioxidants found in organisms ranging from bacteria to humans. They can be divided into two subgroups with either one or two conserved cysteine residues. In plants, 1–Cys peroxiredoxins have been identified in a number of grasses and cereals, and in the dicotyledonous speciesArabidopsis thaliana. In contrast to other antioxidants, the 1–Cys peroxiredoxin genes are expressed solely in seeds, and only in the parts of the seeds surviving desiccation, i.e. the embryo and the aleurone layer. The expression pattern is characteristic of late embryogenesis–abundant genes. The PER1 protein of barley is present in high concentrations in the nucleus at the onset of desiccation. 1–Cys genes are expressed in a dormancy–related manner in mature seeds, in that transcript levels are high in imbibed dormant seeds, but disappear upon germination of their non–dormant counterparts. 1–Cys transcript levels can be up–regulated by ABA and osmotic stresses and suppressed by gibberellic acid. Two hypotheses have been put forward on the function of 1–Cys peroxiredoxins in seed physiology. First, these proteins might protect macromolecules of embryo and aleurone cells against damaging reactive oxygen species during seed desiccation and early imbibition. And second, seed peroxiredoxins might play a role in the maintenance of dormancy. These hypotheses are discussed, taking into account present knowledge of the biochemistry and molecular biology of peroxiredoxins.

Refined solution structure of a liganded type 2 wheat nonspecific lipid transfer protein

The refined structure of a wheat type 2 nonspecific lipid transfer protein (ns-LTP2) liganded with l-alpha-palmitoylphosphatidylglycerol has been determined by NMR. The (15)N-labeled protein was produced in Pichia pastoris. Physicochemical conditions and ligandation were intensively screened to obtain the best NMR spectra quality. This ns-LTP2 is a 67-residue globular protein with a diameter of about 30 A. The structure is composed of five helices forming a right superhelix. The protein presents an inner cavity, which has been measured at 341 A(3). All of the helices display hydrophobic side chains oriented toward the cavity. The phospholipid is found in this cavity. Its fatty acid chain is completely inserted in the protein, the l-alpha-palmitoylphosphatidylglycerol glycerol moiety being located on a positively charged pocket on the surface of the protein. The superhelix structure of the protein is coiled around the fatty acid chain. The overall structure shows similarities with ns-LTP1. Nevertheless, large three-dimensional structural discrepancies are observed for the H3 and H4 alpha-helices, the C-terminal region, and the last turn of the H2 helix. The lipid is orthogonal to the orientation observed in ns-LTP1. The volume of the hydrophobic cavity appears to be in the same range as the one of ns-LTP1, despite the fact that ns-LTP2 is shorter by 24 residues.

Stability of barley aleurone transcripts: Dependence on protein synthesis, influence of the starchy endosperm and destabilization by GA3

We have studied the stability of Barley aleurone and embryo expressed (Balem) transcripts in aleurone layers. The Per1, Ole1 and Ole2 transcripts are abundant during desiccation and in dry resting seeds, while B12D and B22E transcripts are expressed mainly during seed maturation and germination. From 21 to 40 days post anthesis (DPA) incubation of aleurone layers resulted in a substantial, but differential reduction in the levels of these transcripts. In contrast, Balem transcript levels in aleurone layers of incubated embryoless grains were (except for B22E) similar to those of freshly dissected layers. Cycloheximide lowered transcript levels significantly. This indicates that a protein-synthesis-dependent mRNA-stabilizing mechanism is active in the aleurone cells when attached to the starchy endosperm. At the onset of seed desiccation (40 DPA), half-lives of transcripts to be stored in the dry seed were up to several days longer than the half-life of B22E, which decreases during seed maturation. While the Per1, Ole1 and Ole2 transcript levels decline rapidly in the aleurone layers of mature, germinating seeds, the genes are actively transcribed and their transcripts highly stable in the aleurone of incubated embryoless seeds. The expression of Ole1 and Ole2, as well as Per1, can be repressed 100-1 000-fold by gibberellic acid (GA3) in a dose-dependent manner. Abscisic acid can counteract the GA3 repression. Incubations with transcriptional and translational inhibitors indicate that GA3 inhibits the transcription of these genes and at the same time induces a protein-synthesis-dependent mechanism destabilizing their mRNA molecules present.

Disulfide bond assignment, lipid transfer activity and secondary structure of a 7-kDa plant lipid transfer protein, LTP2

The 7-kDa lipid transfer proteins, LTP2s, share some amino-acid sequence similarities with the 9-kDa isoforms, LTP1s. Both proteins display an identical cysteine motif and, in this regard, LTP2s have been classified as lipid transfer proteins. However, in contrast with LTP1s, no data are available on their structure, cysteine pairings, lipid transfer and lipid binding properties. We reported on the isolation of two isoforms of 7-kDa lipid transfer protein, LTP2, from wheat seeds and showed for the first time that they indeed display lipid transfer activity. Trypsin and chymotrypsin digestions of the native LTP2 afforded the sequence of both isoforms and assignment of disulfide bonds. The cysteine pairings, Cys10--Cys24, Cys25--Cys60, Cys2--Cys34, Cys36--Cys67, revealed a mismatch at the Cys34-X-Cys36 motif of LTP2 compared to LTP1. Moreover, the secondary structure as determined by circular dichroism suggested an identical proportion of alpha helices, beta sheets and random coils. By analogy with the structure of the LTP1, we discussed what structural changes are required to accommodate the LTP2 disulfide pattern.

Programmed cell death during endosperm development

The endosperm of cereals functions as a storage tissue in which the majority of starch and seed storage proteins are synthesized. During its development, cereal endosperm initiates a cell death program that eventually affects the entire tissue with the exception of the outermost cells, which differentiate into the aleurone layer and remain living in the mature seed. To date, the cell death program has been described for maize and wheat endosperm, which exhibits common and unique elements for each species. The progression of endosperm programmed cell death (PCD) in both species is accompanied by an increase in nuclease activity and the internucleosomal degradation of nuclear DNA, hallmarks of apoptosis in animals. Moreover, ethylene and abscisic acid are key to mediating PCD in cereal endosperm. The progression of the cell death program in developing maize endosperm follows a highly organized pattern whereas in wheat endosperm, PCD initiates stochastically. Although the essential characteristics of cereal endosperm PCD are now known, the molecular mechanisms responsible for its execution remain to be identified.

Purification and partial characterization of a second cysteine proteinase inhibitor from ungerminated barley (Hordeum vulgare L.)

It was previously shown that ungerminated barley contains inhibitors that suppress the activities of green malt cysteine proteinases. This paper reports the purification and partial characterization of a second barley cysteine endoproteinase inhibitor, a protein called lipid transfer protein 2 (LTP2). The chromatographically purified inhibitor had a molecular mass of 7112. The amino acid composition and sequence data of the purified inhibitor indicated that it was a protein whose gene, but not the protein itself, was isolated earlier from barley aleurone tissue. The purified protein inhibited the activities of electrophoretically separated green malt cysteine proteinases but not the activities of the serine- or metalloproteinases. The purified LTP2 inhibited the same proteases as the LTP1 that was characterized previously but was present in the mature seed in much smaller amounts. Neither LTP1 nor LTP2 has been proven to transport lipids in vivo, and it seems possible that both serve to keep cysteine endoproteinases that are synthesized during barley seed development inactive until the plant needs them. The small amount of LTP2 in the seed made it impossible to determine whether it, like LTP1, is involved in beer foam formation. Because of its proteinase-inhibiting ability and its resistance to heat inactivation, some of the LTP2 may persist in beer.

Characterization of a gene encoding an abscisic acid-inducible type-2 lipid transfer protein from rice

The cloning and sequence analysis of a novel gene that encodes a type 2 non-specific lipid transfer-like protein (LTP) from rice is reported. Sequence analysis revealed an ORF encoding a protein showing characteristics of the LTP proteins. However, rice LTP2 is more similar to heterologous LTPs than to rice LTP1, supporting the existence of two distinct families of plant LTPs. Ltp2 mRNA is accumulated only in mature seeds. In vegetative tissues, mRNA was only detected after treatment with abscisic acid (ABA), mannitol or NaCl. Transient expression experiments that the 61 nucleotides upstream of the TATA box, containing two ACGT boxes and the motif I, are sufficient for ABA responsiveness of the Ltp gene.

A peroxiredoxin antioxidant is encoded by a dormancy-related gene, Per1, expressed during late development in the aleurone and embryo of barley grains

Antioxidants can remove damaging reactive oxygen species produced as by-products of desiccation and respiration during late embryogenesis, imbibition of dormant seeds and germination. We have expressed a protein, PER1, encoded by the Balem (barley aleurone and embryo) transcript previously called B15C, and show it to reduce oxidative damage in vitro. PER1 shares high similarity to a novel group of thiol-requiring antioxidants, named peroxiredoxins, and represents a subgroup with only one conserved cysteine residue (1-Cys). PER1 is the first antioxidant belonging to the 1-Cys subgroup shown to be functionally active, and the first peroxiredoxin of any kind to be functionally described in plants. The steady state level of the transcript, Per1, homologous to a dormancy-related transcript (pBS128) from bromegrass (Bromus secalinus), increases considerably in imbibed embryos from dormant barley (Hordeum vulgare L.) grains. Our investigations also indicate that Per1 transcript levels are dormancy-related in the aleurone layer of whole grains. In contrast to most seed-expressed antioxidants Per1 disappears in germinating embryos, and in the mature aleurone the transcript is down-regulated by the germinating embryo or by gibberellic acid (GA). Our data show that the barley seed peroxiredoxin is encoded by a single Per1 gene. Possible roles of the PER1 peroxiredoxin in barley grains during desiccation, dormancy and imbibition are discussed.

LIPID-TRANSFER PROTEINS IN PLANTS

Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts (as much as 4% of the total soluble proteinss) in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant proteins.

Isolation of a root-specific cDNA encoding a ns-LTP-like protein from the roots of bean (Phaseolus vulgaris L.) seedlings

A root-specific cDNA clone, PVR3, was isolated from a bean (Phaseolus vulgaris L.) root cDNA library by a differential screening procedure. The nucleotide sequence of PVR3 contains an open reading frame coding for an 11.14 kDa polypeptide of 102 amino acid residues; the first 25 amino acids correspond to the sequence characteristic of a signal peptide. Comparison of the deduced PVR3 polypeptide sequence with the polypeptide sequences of previously cloned genes indicates that PVR3 may encode a ns-LTP-like protein. Molecular modelling of the PVR3 protein predicts that it has a three-dimensional structure that is similar to the three-dimensional model determined from the maize ns-LTP. The PVR3 mRNA accumulated mainly in the roots of young seedlings. It can be detected at low levels in flowers, but it is not detected in other organs. Genomic Southern blot analysis indicates that the genomic DNA corresponding to PVR3 cDNA is encoded by a single gene or small gene family in the bean genome.

Evolution of the Group 1 late embryogenesis abundant (Lea) genes: analysis of the Lea B19 gene family in barley

The highly conserved Group 1 late embryogenesis abundant (Lea) genes are present in the genome of most plants as a gene family. Family members are conserved along the entire coding region, especially within the extremely hydrophilic internal 20 amino acid motif, which may be repeated. Cloning of Lea Group 1 genes from barley resulted in the characterization of four family members named B19.1, B19.1b, B19.3 and B19.4 after the presence of this motif 1, 1, 3 and 4 times in each gene, respectively. We present here the results of comparative and evolutionary analyses of the barley Group 1 Lea gene family (B19). The most important findings resulting from this work are (1) the tandem clustering of B19.3 and B19.4, (2) the spatial conservation of putative regulatory elements between the four B19 gene promoters, (3) the determination of the relative 'age' of the gene family members and (4) the 'chimeric' nature of B19.3 and B19.4, reflecting a cross-over or gene-conversion event in their common ancestor. We also show evidence for the presence of one or two additional expressed B19 genes in the barley genome. Based on our results, we present a model for the evolution of the family in barley, including the 20 amino acid motif. Comparisons of the relatedness between the barley family and all other known Group 1 Lea genes using maximum parsimony (PAUP) analysis provide evidence for the time of divergence between the barley genes containing the internal motif as a single copy and as a repeat. The PAUP analyses also provide evidence for independent duplications of Group 1 genes containing the internal motif as a repeat in both monocots and dicots.

The transcripts encoding two oleosin isoforms are both present in the aleurone and in the embryo of barley (Hordeum vulgare L.) seeds

Two transcripts (Ole-1 and Ole-2) encoding two oleosin isoforms homologous to the 18 and 16 kDa oleosins of maize, respectively, have been isolated from developing barley embryos and aleurone layers where lipid bodies are highly abundant organelles. For each of the isoforms the aleurone and embryo transcripts are identical, indicating that the same genes are expressed in both tissues. The temporal accumulation of the two transcripts during seed development is similar. At a low frequency, lipid bodies are found also in starchy endosperm cells of barley. Accordingly, a low transcript level is observed for both oleosins during starchy endosperm development.

A fatty-acid-binding protein from wheat kernels

A protein of about 7 kDa (W-FABP) has been isolated from mature wheat kernels by H2O extraction and gel filtration of the extract, followed by two steps of high-performance liquid chromatography. The N-terminal amino acid-sequence has been determined up to the 28th residue and found to be identical (except for positions 4 and 5) to that deduced from a barley cDNA (EMBL X15257), which had been improperly classified as a non-specific lipid transfer protein (LTP2). Similarly with LTPs, W-FABP does bind fatty acids, but in contrast, it is not significantly homologous to LTPs, it is not recognized by LTP antibodies, it has a more acidic isoelectric point (pH < 6.8 vs. pH > 9.6), and it does not show antibiotic properties.

Characterization of a rice gene coding for a lipid transfer protein

The cloning and sequence analysis of a gene that encodes a lipid transfer protein (LTP) from rice is reported. A genomic DNA library from Oryza sativa was screened using a cDNA encoding a maize LTP. One genomic clone containing the gene (Ltp) was partially sequenced and analyzed. The open reading frame is interrupted by an 89-bp intron. From the results of Southern hybridizations, Ltp appears to be a member of a small multigenic family. Transcripts of the corresponding gene were detected in several tissues including coleoptile, leaf, endosperm, scutellum and root. The transcription start point was determined by primer extension. The deduced amino-acid sequence of the Ltp product is shown to be homologous to LTPs from other crops.

PCR amplification and sequences of cDNA clones for the small and large subunits of ADP-glucose pyrophosphorylase from barley tissues

Several cDNAs encoding the small and large subunit of ADP-glucose pyrophosphorylase (AGP) were isolated from total RNA of the starchy endosperm, roots and leaves of barley by polymerase chain reaction (PCR). Sets of degenerate oligonucleotide primers, based on previously published conserved amino acid sequences of plant AGP, were used for synthesis and amplification of the cDNAs. For either the endosperm, roots and leaves, the restriction analysis of PCR products (ca. 550 nucleotides each) has revealed heterogeneity, suggesting presence of three transcripts for AGP in the endosperm and roots, and up to two AGP transcripts in the leaf tissue. Based on the derived amino acid sequences, two clones from the endosperm, beps and bepl, were identified as coding for the small and large subunit of AGP, respectively, while a leaf transcript (blpl) encoded the putative large subunit of AGP. There was about 50% identity between the endosperm clones, and both of them were about 60% identical to the leaf cDNA. Northern blot analysis has indicated that beps and bepl are expressed in both the endosperm and roots, while blpl is detectable only in leaves. Application of the PCR technique in studies on gene structure and gene expression of plant AGP is discussed.

Late embryogenesis-abundant genes encoding proteins with different numbers of hydrophilic repeats are regulated differentially by abscisic acid and osmotic stress

The late embryogenesis-abundant (Lea) genes, which are suggested to act as desiccation protectants during seed desiccation and in water-stressed seedlings, can be induced by abscisic acid (ABA) and various kinds of water-related stress. Using cotton Lea cDNAs as probes it was found that several of the Lea genes are conserved at the mRNA level in dicots and monocots. By screening a barley cDNA library with a cotton Lea D19 cDNA a family of three members was isolated. The putative B19 proteins have strong similarities to the Em protein in wheat and to LEA proteins from several dicots. However, the middle part of the B19 proteins consists of a 20-amino acid motif repeated three and four times in B19.3 and B19.4, respectively, but only once in B19.1. The gene products are strongly hydrophilic, the internal 20-amino acid motif being the most hydrophilic part. This motif is found once in cotton Lea D19 but is repeated twice in cotton Lea D132, indicating that the repeats are universal among monocot and dicot B19-like genes. The B19 genes are regulated similarly during embryo development, but to very different levels. In contrast, they are differentially regulated by ABA and various types of osmotic stress. In immature embryos all three genes are responsive to ABA and mannitol. However, B19.1 is also responsive to salt. Cold stress does not induce B19 mRNAs; only a stabilization of the transcript levels is seen. These results suggest that the responses to salt stress and exogenous ABA operate through different pathways.

Primary structure of a novel barley gene differentially expressed in immature aleurone layers

As a direct approach to elucidate the molecular biology of barley aleurone cell development, we differentially screened an aleurone cDNA library made from poly(A)+ RNA of immature grains for clones representing transcripts present in the aleurone but not in the starchy endosperm. For one of these clones, B22E, which hybridies to a 0.7 kb transcript, Northern and in situ hybridization revealed that expression is under complex spatial, temporal and hormonal control in barley grains. cDNAs corresponding to B22E transcripts were isolated from aleurone/pericarp and embryo of developing grains, and from germinating scutella. Among these were the nearly full-length aleurone/pericarp clone pB22E.a16 (541 bp). cDNAs matching the sequence of this clone (type 1 transcript) were found for all tissues investigated. In addition, cDNAs with an extra 12 bp insertion (type 2 transcript) were obtained from germinating scutella. The two different transcripts can encode novel barley proteins of 115 and 119 amino acids, respectively. A gene designated B22EL8 was isolated and sequenced; it encodes the type 1 B22E transcript and contains two introns of 145 and 125 bp. Particle bombardment of barley aleurone with a B22EL8 promoter-GUS (beta-glucuronidase) construct demonstrates that the promoter (3 kb) is active in developing barley grains. The promoter is not, however, active in the seeds of tobacco plants transgenic for the B22EL8 gene, indicating the existence of sequences specific for monocots. A comparison of 1.4 kb of upstream sequence of B22E with the maize c1 promoter reveals a number of short, identical sequences which may be responsible for aleurone cell-specific gene transcription.

An embryo-specific protein of barley (Hordeum vulgare)

An immunological approach has been used to identify embryo-specific products that can be used as molecular markers of embryogenesis. Immunoadsorption of antisera to remove antigens common to embryos, meristematic cells and callus, revealed one major embryo-specific antigen, a polypeptide of 17 kDa. The antigen appeared at mid-stages of zygotic embryo formation and remained at similar levels up to six days post-germination of the seedling. The polypeptide could not be detected by protein staining, suggesting it is a non-abundant product. Appearance of the antigen could be induced by culture of zygotic embryos in vitro on abscisic acid (1 microM) or mannitol (9% mass/vol.). Cross-reactive products of near-identical molecular mass were observed in embryos of wheat, rye and oats but not distantly related cereals, nor embryos from dicotyledonous species. The timing of the appearance of the antigen was different in embryos formed from microspores during anther culture in vitro. In the cultured material, the 17-kDa polypeptide preceded the appearance of morphologically distinct embryonic structure.