Ternary complex formation between HvMYBS3 and other factors involved in transcriptional control in barley seeds

The SHAQKYF R1MYB transcription factor (TF) HvMYBS3 from barley is an activator of gene expression both during endosperm development and in aleurone cells upon seed germination. Its mRNA was detected as early as 10 days after flowering in developing barley endosperm, with a peak at 18 days, and in aleurone cells at 8 h after water imbibition, as shown by Northern blot and in situ hybridization analyses. The HvMYBS3 protein expressed in bacteria binds to oligonucleotides containing a GATA core derived from the promoters of: (i) the developing endosperm gene Itr1 (5'-GATAAGATA-3') encoding trypsin inhibitor BTI-CMe, and (ii) the post-germinating aleurone gene Amy6.4 (5'-TATCCAC-3'/5'-GTGGATA-3') encoding a high-pI alpha-amylase. Transient expression experiments in co-bombarded developing endosperms and in barley aleurone layers demonstrated that HvMYBS3 trans-activated transcription both from Itr1 and Amy6.4 promoters, in contrast with a previously reported seed-expressed R1MYB, HvMCB1, which was an activator of Itr1 and a transcriptional repressor of the Amy6.4 gene. In the yeast three-hybrid system, the HvMYBS3 protein formed a ternary complex with BPBF and BLZ2, two important seed TFs. However, no binary interactions could be detected between HvMYBS3 and BLZ2 or between HvMYBS3 and BPBF.

Barley anther culture: effects of annual cycle and spike position on microspore embryogenesis and albinism

The effect of donor plants annual cycle and anther/spike position on the production of microspore-derived plants and albinism were studied. We used the winter cv. Igri and the spring cv. Cork, known to respond similarly in anther culture but to produce 78% and 2% of green plants, respectively. In both cvs. the number of microspore-derived plants was significantly higher when the anthers were collected from January to July than from August to December. However, during this period the proportion of albino plants was not altered. Conversely, the anther response decreased from 76.6 to 31.5% in Igri and from 58.8 to 32.0% in Cork when the donor spike originates from the main shoot or the fourth tiller. Significantly, anthers collected from spike of the second tiller enabled us to drastically increase the proportion of regenerated green plantlets, by 16% in Igri and 1800% in Cork.

Abundant transcripts of malting barley identified by serial analysis of gene expression (SAGE)

Serial analysis of gene expression (SAGE) was applied to the major cereal crop barley (Hordeum vulgare) to characterize the transcriptional profile of grain during the malting process. Seven SAGE libraries were generated from seed at different time points during malting, in addition to one library from dry mature seed. A total of 155,206 LongSAGE tags, representing 41,909 unique sequences, was generated. This study reports an in-depth analysis of the most abundant transcripts from each of eight specific time points in a malting barley time course. The 100 most abundant tags from each library were analysed to identify the putative functional role of highly abundant transcripts. The largest functional groups included transcripts coding for stress response and cell defence, ribosomal proteins and storage proteins. The most abundant tag represented B22EL8, a barley metallothionein, which showed significant up-regulation across the malting time course. Considerable changes in the abundance profiles of some of the highly abundant tags occurred at 24 h post-steeping, indicating that it may be an important time point for gene expression changes associated with barley seed germination.

Transgenic barley plants overexpressing a 13-lipoxygenase to modify oxylipin signature

Three chimeric gene constructs were designed comprising the full length cDNA of a lipoxygenase (LOX) from barley (LOX2:Hv:1) including its chloroplast targeting sequence (cTP) under control of either (1) CaMV35S- or (2) polyubiquitin-1-promoter, whereas the third plasmid contains 35S promoter and the cDNA without cTP. Transgenic barley plants overexpressing LOX2:Hv:1 were generated by biolistics of scutella from immature embryos. Transformation frequency for 35S::LOX with or without cTP was in a range known for barley particle bombardment, whereas for Ubi::cTP-LOX no transgenic plants were detected. In general, a high number of green plantlets selected on bialaphos became yellow and finally died either in vitro or after potting. All transgenic plants obtained were phenotypically indistinguishable from wild type plants and all of them set seeds. The corresponding protein (LOX-100) in transgenic T0 and T1 plants accumulated constitutively to similar levels as in the jasmonic acid methyl ester (JAME)-treated wild type plants. Moreover, LOX-100 was clearly detectable immunocytochemically within the chloroplasts of untreated T0 plants containing the LOX-100-cDNA with the chloroplast target sequence. In contrast, an exclusive localization of LOX-100 in the cytoplasm was detectable when the target sequence was removed. In comparison to sorbitol-treated wild type leaves, analysis of oxylipin profiles in T2 progenies showed higher levels of jasmonic acid (JA) for those lines that displayed elevated levels of LOX-100 in the chloroplasts and for those lines that harboured LOX-100 in the cytoplasm, respectively. The studies demonstrate for the first time the constitutive overexpression of a cDNA coding for a 13-LOX in a monocotyledonous species and indicate a link between the occurrence of LOX-100 and senescence.

Oxygen deficiency in barley (Hordeum vulgare) grain during malting

The steep water is generally aerated in industrial barley malting. However, it is questionable whether oxygen actually reaches the embryo, which remains entrapped under the husk, testa, and pericarp until chitting occurs. The aim of our study was to investigate whether barley embryos experience oxygen deficiency during steeping, and whether various steeping conditions affect the oxygen deficiency. Alcohol dehydrogenase Adh2 was induced in all steeping conditions studied. Therefore, oxygen deficiency occurred regardless of the steeping conditions. However, steeping conditions affected the rate of recovery from oxygen deficiency, germination rate, and onset of alpha-amylase production. When barley was subjected to oxygen deficiency by applying N(2) gas during steeping, the timing of the treatment determined its effects. The importance of aeration increased as the process proceeded. Oxygen deprivation at the beginning of the process had little effect on malt quality. Therefore, the timing of aeration is important in the optimization of germination during the steeping stage of malting.

Hypoxia interferes with ABA metabolism and increases ABA sensitivity in embryos of dormant barley grains

Two mechanisms have been suggested as being responsible for dormancy in barley grain: (i) ABA in the embryo, and (ii) limitation of oxygen supply to the embryo by oxygen fixation as a result of the oxidation of phenolic compounds in the glumellae. The aim of the present work was to investigate whether hypoxia imposed by the glumellae interferes with ABA metabolism in the embryo, thus resulting in dormancy. In dormant and non-dormant grains incubated at 20 degrees C and in non-dormant grains incubated at 30 degrees C (i.e. when dormancy is not expressed), ABA content in the embryo decreased dramatically during the first 5 h of incubation before germination was detected. By contrast, germination of dormant grains was less than 2% within 48 h at 30 degrees C and embryo ABA content increased during the first hours of incubation and then remained 2-4 times higher than in embryos from grains in which dormancy was not expressed. Removal of the glumellae allowed germination of dormant grains at 30 degrees C and the embryos did not display the initial increase in ABA content. Incubation of de-hulled grains under 5% oxygen to mimic the effect of glumellae, restored the initial increase ABA in content and completely inhibited germination. Incubation of embryos isolated from dormant grains, in the presence of a wide range of ABA concentrations and under various oxygen tensions, revealed that hypoxia increased embryo sensitivity to ABA by 2-fold. This effect was more pronounced at 30 degrees C than at 20 degrees C. Furthermore, when embryos from dormant grains were incubated at 30 degrees C in the presence of 10 microM ABA, their endogenous ABA content remained constant after 48 h of incubation under air, while it increased dramatically in embryos incubated under hypoxia, indicating that the apparent increase in embryo ABA responsiveness induced by hypoxia was, in part, mediated by an inability of the embryo to inactivate ABA. Taken together these results suggest that hypoxia, either imposed artificially or by the glumellae, increases embryo sensitivity to ABA and interferes with ABA metabolism.

Hordeins are expressed in microspore-derived embryos and also during male gametophytic and very early stages of seed development

Microspore-derived embryos induced by anther or isolated-microspore culture display certain characteristics of zygotic embryos. Furthermore, the expression of certain endosperm genes has been described in these non-zygotic embryos. The expression of hordein genes encoding the main barley endosperm proteins has been studied using a wide range of methods (RT-PCR, in situ hybridization, ELISA sandwich, western blotting immunocytochemistry, and cytochemistry) to ascertain their presence or absence during the induction and first stages of microspore embryogenesis. Due to the very sensitive techniques used it was possible to detect for the first time hordein expression during microspore embryogenesis. Surprisingly, these hordeins were also detected at different stages of male gametophytic development as well as during the very early stages of seed development, when they have not hitherto been detected. The expression and localization of these storage proteins and their corresponding transcripts provide new information about barley microspore embryogenesis and its relationship to zygotic embryogenesis. Although only small quantities of hordeins are accumulated during microspore embryogenesis they seem to be necessary for the initial development of the microspore-derived embryo. This idea is supported by the changes detected in their concentration throughout this process and is in accordance with previously published data concerning the importance of endosperm proteins for embryo development in both microspore culture and in planta.

HvMCB1, a R1MYB transcription factor from barley with antagonistic regulatory functions during seed development and germination

The functional analysis of hydrolase gene promoters induced by gibberellin (GA) in barley aleurone cells upon germination has identified a tripartite GA-response complex (GARC) containing a 5'-TATCCAC-3' box as well as the GA-responsive element (GARE) recognized by GAMYB and the pyrimidine box interacting with the DOF transcription factors BPBF and SAD. We show here that the MCB1 gene encoding a R1MYB protein binds to the 5'-TATCCAC-3' (GATA core) box in vitro and is a transcriptional repressor of a GA-induced amylase (Amy6.4) promoter in bombarded aleurone layers. Northern blot and mRNA in situ hybridization analyses showed that the MCB1 transcripts accumulate in the aleurone cells upon germination, as well as in endosperm tissues during seed development. The HvMCB1 protein expressed in bacteria binds in a specific manner to a 27-mer oligonucleotide containing the 5'-TATCCAC-3' sequence, derived from the promoter region of the Amy6.4 gene. Accumulation of the MCB1 transcript diminished in response to external GA incubation in aleurone cells, and in transient expression experiments HvMCB1 repressed transcription of the Amy6.4 promoter in GA-treated aleurone layers and reversed the GAMYB-mediated activation of this amylase promoter. In contrast, during endosperm maturation HvMCB1 acted as a transcription activator of the seed-specific Itr1 gene promoter through binding to a 5'-GATAAGATA-3' box.

Three dimensional confocal and electron microscopy imaging define the dynamics and mechanisms of diploidisation at early stages of barley microspore-derived embryogenesis

In order to determine the timing and mechanisms of the spontaneous diploidisation throughout microspore-derived embryogenesis in barley, we have estimated the ploidy level of individual nuclei within young pro-embryos, from the first androgenetic division up to multinuclear structures still surrounded by the exine. Our methodological approach was based on the measure of the intensity of fluorescence after 4,6-Diamidino-2-phenylindole dihydrochloride staining, nuclear size and number of nucleoli in the confocal microscope. This method avoids the overlapping of the fluorescence signal in multinuclear pro-embryos, which cannot be studied using cytophotometer methods based on other types of fluorescence microscopes. The identification of haploid and diploid nuclei enabled us to determine the timing of diploidisation at early stages throughout androgenetic development. We found that diploidisation is an ongoing process that can start after the first embryogenic division and continues in multinuclear pro-embryos. Reconstruction of 3D-images of entire pro-embryos and the observation of cross and longitudinal sections across stacks of optical sections, together with correlative light and electron microscopy, provided evidences of nuclear fusion as the main mechanism of diploidisation.

Mature embryo axis-based high frequency somatic embryogenesis and plant regeneration from multiple cultivars of barley (Hordeum vulgare L.)

A highly reproducible regeneration system through somatic embryogenesis from the excised mature embryos (MEs) of dry seeds of a range of European barley cultivars was developed. By minimizing the germination of plated MEs, primary callus could be obtained with high frequency which permitted efficient embryogenesis and regeneration of a large number of green plants. Different approaches were tested to reduce or prevent normal germination: (i) the use of a well defined balance of maltose and 2,4-D in the induction medium, (ii) soaking of seeds in water containing 2,4-D solution, (iii) direct culture of excised embryonic axes, (iv) longitudinally bisected MEs giving two halves, and (v) complete removal of the elongated main shoot including any roots within a week of culture initiation. Culturing of bisected MEs and whole embryonic axes gave the best responses with respect to large amounts of callus combined with minimal germination. The incorporation of BAP at low levels in the medium was found to be most effective for embryogenesis and the maintenance of long-term morphogenic capacity (more than 11 months up to now). This procedure allows the complete regeneration of plants in 16-20 weeks, from the initial isolation of MEs through all the steps to the development of plants ready to be transferred to the soil. The protocol was first developed for cv. Golden Promise and successfully applied to commercial cultivars. All cultivars tested formed embryogenic callus, with overall rates ranging from 22-55% and an average number of green plants per embryogenic callus from 1.5 to 7.5 across the genotypes.

Changes in cell wall polysaccharides in developing barley (Hordeum vulgare) coleoptiles

Cell wall polysaccharides in developing barley coleoptiles were examined using acetic acid-nitric acid extraction, alditol acetate and methylation analyses and enzymatic digestion. The coleoptile cell wall from imbibed grain was rich in pectic polysaccharides (30 mol%), arabinoxylan (25 mol%), cellulose (25 mol%) and xyloglucan (6 mol%), but contained only low levels of (1-->3,1-->4)-beta-D-glucan (1 mol%). During 5 days of coleoptile growth, pectic polysaccharides decreased steadily to about 9 mol%, while (1-->3,1-->4)-beta-D-glucan increased to 10 mol%. Following the cessation of growth of the coleoptiles at about 5 days, (1-->3,1-->4)-beta-D-glucan content rapidly decreased to 1 mol%. The cellulose content of the walls remained at about 35-40 mol% throughout coleoptile growth. Similarly, arabinoxylan content remained essentially constant at 25-30 mol% during growth, although the ratio of substituted to unsubstituted 4-linked xylosyl units decreased from about 4:1 to 1:1. Xyloglucan content ranged from 6 mol% to 10 mol% and the oligosaccharide profile determined using a xyloglucan-specific endoglucanase and MALDI-TOF mass spectrometry indicated that the oligosaccharides XXGG and XXGGG were the principal components, with one and two acetyl groups, respectively, Thus, dramatic changes in wall composition were detected during the growth of barley coleoptiles, both with respect to the relative abundance of individual wall constituents and to the fine structure of the arabinoxylans.

Programmed cell death during the transition from multicellular structures to globular embryos in barley androgenesis

Androgenesis represents one of the most fascinating examples of cell differentiation in plants. In barley, the conversion of stressed uninucleate microspores into embryo-like structures is highly efficient. One of the bottlenecks in this process is the successful release of embryo-like structures out of the exine wall of microspores. In the present work, morphological and biochemical studies were performed during the transition from multicellular structures to globular embryos. Exine wall rupture and subsequent globular embryo formation were observed only in microspores that divided asymmetrically. Independent divisions of the generative and the vegetative nuclei gave rise to heterogeneous multicellular structures, which were composed of two different cellular domains: small cells with condensed chromatin structure and large cells with normal chromatin structure. During exine wall rupture, the small cells died and their death marked the site of exine wall rupture. Cell death in the small cell domain showed typical features of plant programmed cell death. Chromatin condensation and DNA degradation preceded cell detachment and cytoplasm dismantling, a process that was characterized by the formation of vesicles and vacuoles that contained cytoplasmic material. This morphotype of programmed cell death was accompanied by an increase in the activity of caspase-3-like proteases. The orchestration of such a death program culminated in the elimination of the small generative domain, and further embryogenesis was carried out by the large vegetative domain. To date, this is the first report to show evidence that programmed cell death takes part in the development of microspore-derived embryos.

Identification of thioredoxin?h-reducible disulphides in proteomes by differential labelling of cysteines: Insight into recognition and regulation of proteins in barley seeds by thioredoxin?h

Using thiol-specific fluorescence labelling, over 30 putative target proteins of thioredoxin h with diverse structures and functions have been identified in seeds of barley and other plants. To gain insight at the structural level into the specificity of target protein reduction by thioredoxin h, thioredoxin h-reducible disulphide bonds in individual target proteins are identified using a novel strategy based on differential alkylation of cysteine thiol groups by iodoacetamide and 4-vinylpyridine. This method enables the accessible cysteine side chains in the thiol form (carbamidomethylated) to be distinguished from those inaccessible or disulphide bound form (pyridylethylated) according to the mass difference in the peptide mass maps obtained by matrix-assistend laser desorption/ionisation-time of flight mass spectrometry. Using this approach, in vitro reduction of disulphides in recombinant barley alpha-amylase/subtilisin inhibitor (BASI) by barley thioredoxin h isoform 1 was analysed. Furthermore, the method was coupled with two-dimensional electrophoresis for convenient thioredoxin h-reducible disulphide identification in barley seed extracts without the need for protein purification or production of recombinant proteins. Mass shifts of 15 peptides, induced by treatment with thioredoxin h and differential alkylation, identified specific reduction of nine disulphides in BASI, four alpha-amylase/trypsin inhibitors and a protein of unknown function. Two specific disulphides, located structurally close to the alpha-amylase binding surfaces of BASI and alpha-amylase inhibitor BMAI-1 were demonstrated to be reduced to a particularly high extent. For the first time, specificity of thioredoxin h for particular disulphide bonds is demonstrated, providing a basis to study structural aspects of the recognition mechanism and regulation of target proteins.

The complex developmental expression of a novel stress-responsive barley Ltp gene is determined by a shortened promoter sequence

The search for a cereal promoter capable of driving preferential transgene expression in the pericarp epidermis (epicarp) of developing barley (Hordeum vulgare L.) resulted in the cloning of a novel gene. This encoded a polypeptide of 124 amino acids showing 87 identity with WBP1A, a wheat lipid transfer protein (LTP), but much lower homology to other barley LTPs. In addition to the epicarp, this Ltp-like gene, Ltp6, is highly expressed in coleoptiles and embryos under normal growth conditions. Messenger RNA levels increased in seedling tissues during salt and cold treatments and under applied abscisic acid (ABA) and salicylic acid (SA). Taken together, Ltp6 tissue-specific and response patterns are distinct from other known barley Ltp genes. Inverse PCR was used to derive 2345 bp of upstream Ltp6 sequence. The level of transcription conferred by different promoter deletion constructs was assessed by quantitative real time RT-PCR using gfp as a reporter in transient expression assays. All constructs containing at least 192 bp of upstream sequence and the 5'UTR conferred tissue-specific expression and retained most of the promoter strength. Deletion of 64 bp (-192/-128) from this upstream sequence reduced expression levels by 80. Moreover, a minimal 247 bp Ltp6 promoter continuously drove gfp expression during spike development, from early ovary differentiation through its final expression in the epicarp and during embryogenesis and germination in transgenic barley, reproducing the expression pattern of the native gene. The potential use of this promoter sequence for targeting transgene-mediated disease resistance in barley and wheat is discussed.

Efficient regeneration of fertile barley plants from callus cultures of several Nordic cultivars

The regeneration potential of three major Estonian barley cultivars was tested and compared to that of the Finnish cultivar Kymppi. Two different regeneration systems were used. The first was characterized by the high maltose concentration (60 g l(-1)) and by the use of 2,4D together with two different combinations of amino acids in the callus induction medium followed by the regeneration medium containing BAP (2 mg l(-1)) and 2,4D (0.2 mg l(-1)). The second exploited callus induction medium that contained Dicamba, lower concentrations of maltose (30 g l(-1)) and higher concentrations of myo-inositol and thiamine and different set of amino acids and regeneration medium that contained higher concentrations of Cu2+ and inorganic nitrogen accompanied by lower concentrations of NH4+ and BAP, when compared to the first regeneration system. The second regeneration system used produced significantly higher rates of callus induction, callus growth and regeneration of plantlets. However, it yielded also many albino plants (up to 51%), whereas the first regeneration system used did not produce practically any albino plants. No major genotype-dependent differences were observed in comparison between two regeneration systems - in both systems higher regeneration potential of Anni, Elo and Kymppi contradicted to the low regeneration potential of Teele. It is concluded that the continuous somatic embryogenesis on the regeneration medium allows the regeneration of many plants from the same callus over long periods of time and makes available highly efficient regeneration protocols for Estonian and Finnish barley cultivars.

A highly efficient plant regeneration system through multiple shoot differentiation from commercial cultivars of barley (Hordeum vulgare L.) using meristematic shoot segments excised from germinated mature embryos

A fast and highly efficient short-term in vitro regeneration system was developed for barley (Hordeum vulgare L.) based on readily available explants. Clumps of multiple shoots and buds suitable for transformation were obtained 9-10 weeks after culture initiation from model and current commercial cultivars. Meristematic shoot segments (MSSs) excised from mature embryo-derived seedlings and subsequently cultured on MS-based medium containing 2 mg/l Picloram and 3 mg/l thidiazuron (TDZ) differentiated up to ten multiple shoots after 3-4 weeks with no or very little callus formation. Sectors of the already multiplied shoot clumps were further multiplied on proliferation-maintenance medium containing 2 mg/l Picloram and 2.5 mg/l TDZ. Biweekly subcultures resulted in a continuous process of multiplication of these highly differentiating green sectors without any loss of morphogenic potential. The differentiated small shoots and shoot buds gave rise to normal shoots on medium with 0.1 mg/l Picloram and 1 mg/l TDZ. After rooting on basal medium with 0.5 mg/l or 1 mg/l IBA the plants were transferred to soil and showed normal growth and fertility compared to the seed-grown plants. All of the genotypes tested formed multiple shoots. The percentage of relative MSS multiplication was 63-83%, and the average number of multiplied shoots per MSS ranged from 16 to 34 among the genotypes after 9-11 weeks.

High frequency plant regeneration from immature embryos of an elite barley cultivar (Hordeum vulgare L. cv. Morex)

An efficient plant regeneration system was developed for Hordeum vulgare L. 'Morex' barley, an important United States malting cultivar. The protocol was based on a series of experiments involving the sizes of immature embryos and the culture media. We found that the embryo size is critical for the establishment of embryogenic callus. Smaller embryos (0.5-1.5 mm) showed a much higher ability to produce embryogenic callus capable of regenerating green plants with fewer albinos than did the larger embryos (1.6-3.0 mm). Either 3 mg/l 2,4-dichlorophenoxyacetic acid or dicamba in modified Murashige and Skoog's (MS) medium was optimum for the induction of embryogenic callus. The embryogenic callus maintained high regeneration during six subcultures in the callus induction medium. Efficient shoot regeneration was obtained on modified MS medium containing 0.5-1.0 mg/l 6-benzylaminopurine (BA). Regenerated shoots were rooted on half-strength MS medium containing 0.2 mg/l IBA. Plants were successfully transferred to soil and grown to maturity in the greenhouse. This efficient plant regeneration system provides a foundation for generating transgenic plants of this important barley cultivar.

14-3-3 isoforms and pattern formation during barley microspore embryogenesis

The members of the 14-3-3 isoform family have been shown to be developmentally regulated during animal embryogenesis, where they take part in cell differentiation processes. 14-3-3 isoform-specific expression patterns were studied in plant embryogenic processes, using barley (Hordeum vulgare L.) microspore embryogenesis as a model system. After embryogenesis induction by stress, microspores with enlarged morphology showed higher viability than non-enlarged ones. Following microspore culture, cell division was only observed among the enlarged microspores. Western blot and immunolocalization of three barley 14-3-3 isoforms, 14-3-3A, 14-3-3B and 14-3-3C were carried out using isoform-specific antibodies. The level of 14-3-3C protein was higher in enlarged microspores than in non-enlarged ones. A processed form of 14-3-3A was associated with the death pathway of the non-enlarged microspores. In the early embryogenesis stage, 14-3-3 subcellular localization differed among dividing and non-dividing microspores and the microspore-derived multicellular structures showed a polarized expression pattern of 14-3-3C and a higher 14-3-3A signal in epidermis primordia. In the late embryogenesis stage, 14-3-3C was specifically expressed underneath the L(1) layer of the shoot apical meristem and in the scutellum of embryo-like structures (ELSs). 14-3-3C was also expressed in the scutellum and underneath the L(1) layer of the shoot apical meristem of 21 d after pollination (DAP) zygotic embryos. These results reveal that 14-3-3A processing and 14-3-3C isoform tissue-specific expression are closely related to cell fate and initiation of specific cell type differentiation, providing a new insight into the study of 14-3-3 proteins in plant embryogenesis.

Transgenic barley grain overexpressing thioredoxin shows evidence that the starchy endosperm communicates with the embryo and the aleurone

Homozygous lines of barley overexpressing a wheat thioredoxin h transgene (up to 30-fold) were generated earlier by using a B(1)-hordein promoter with a signal peptide sequence for targeting to the protein body and found to be enriched in starch debranching enzyme (pullulanase). Here, we describe the effect of biochemically active, overexpressed thioredoxin h on germination and the onset of alpha-amylase activity. Relative to null segregant controls lacking the transgene, homozygotes overexpressing thioredoxin h effected (i) an acceleration in the rate of germination and appearance of alpha-amylase activity with a 1.6- to 2.8-fold increase in gibberellin A(1) (GA(1)) content; (ii) a similar acceleration in the appearance of the alpha-amylase activity in deembryonated transgenic grain incubated with gibberellic acid; (iii) a 35% increase in the ratio of relative reduction (abundance of SH) of the propanol soluble proteins (hordein I fraction); and (iv) an increase in extractable and soluble protein of 5-12% and 11-35%, respectively. Thioredoxin h, which was highly reduced in the dry grain, was degraded in both the null segregant and homozygote after imbibition. The increase in alpha-amylase activity and protein reduction status was accompanied by a shift in the distribution of protein from the insoluble to the soluble fraction. The results provide evidence that thioredoxin h of the starchy endosperm communicates with adjoining tissues, thereby regulating their activities, notably by accelerating germination of the embryo and the appearance of alpha-amylase released by the aleurone.

Cold-regulated cereal chloroplast late embryogenesis abundant-like proteins. Molecular characterization and functional analyses

Cold acclimation and freezing tolerance are the result of complex interaction between low temperature, light, and photosystem II (PSII) excitation pressure. Previous results have shown that expression of the Wcs19 gene is correlated with PSII excitation pressure measured in vivo as the relative reduction state of PSII. Using cDNA library screening and data mining, we have identified three different groups of proteins, late embryogenesis abundant (LEA) 3-L1, LEA3-L2, and LEA3-L3, sharing identities with WCS19. These groups represent a new class of proteins in cereals related to group 3 LEA proteins. They share important characteristics such as a sorting signal that is predicted to target them to either the chloroplast or mitochondria and a C-terminal sequence that may be involved in oligomerization. The results of subcellular fractionation, immunolocalization by electron microscopy and the analyses of target sequences within the Wcs19 gene are consistent with the localization of WCS19 within the chloroplast stroma of wheat (Triticum aestivum) and rye (Secale cereale). Western analysis showed that the accumulation of chloroplastic LEA3-L2 proteins is correlated with the capacity of different wheat and rye cultivars to develop freezing tolerance. Arabidopsis was transformed with the Wcs19 gene and the transgenic plants showed a significant increase in their freezing tolerance. This increase was only evident in cold-acclimated plants. The putative function of this protein in the enhancement of freezing tolerance is discussed.

Differential gene expression during seed germination in barley (Hordeum vulgare L.)

A barley cDNA macroarray comprising 1,440 unique genes was used to analyze the spatial and temporal patterns of gene expression in embryo, scutellum and endosperm tissue during different stages of germination. Among the set of expressed genes, 69 displayed the highest mRNA level in endosperm tissue, 58 were up-regulated in both embryo and scutellum, 11 were specifically expressed in the embryo and 16 in scutellum tissue. Based on Blast X analyses, 70% of the differentially expressed genes could be assigned a putative function. One set of genes, expressed in both embryo and scutellum tissue, included functions in cell division, protein translation, nucleotide metabolism, carbohydrate metabolism and some transporters. The other set of genes expressed in endosperm encodes several metabolic pathways including carbohydrate and amino acid metabolism as well as protease inhibitors and storage proteins. As shown for a storage protein and a trypsin inhibitor, the endosperm of the germinating barley grain contains a considerable amount of residual mRNA which was produced during seed development and which is degraded during early stages of germination. Based on similar expression patterns in the endosperm tissue, we identified 29 genes which may undergo the same degradation process.

Reversed-phase liquid chromatographic determination of phytometallophores from Strategy II Fe-uptake species by 9-fluorenylmethyl chloroformate fluorescence

An HPLC method to quantitate phytometallophores (phytosiderophores) exuded from roots of barley (Hordeum vulgare L.) growing in nutrient solution culture was developed. 9-Fluorenylmethyl chloroformate (FMOC) derivatives of phytometallophores were separated on a C18 reverse-phase column using a sodium acetate (pH 7.2) and acetonitrile-methanol gradient over 20 min followed by fluorescence detection. Detection limits ranged from 15 to 370 pmol depending on the particular phytometallophore. The effectiveness of this method was demonstrated using the response of barley seedlings to Fe-sufficient and Fe-deficient nutrient solution conditions. Phytometallophores collected in root washings of Fe-deficient barley seedlings increased with plant age while phytometallophore release from Fe-adequate roots was negligible.

EPR studies on gamma-irradiated barley seeds: identification of trapped electrons

Electron paramagnetic resonance (EPR) studies were conducted on barley seeds exposed to normal (H(2)O) and deuterated (D(2)O) moisture, irradiated with 750 Gy at 77 K. Reported here, for the first time, are the trapped electrons formed on gamma-irradiation of seeds at 77 K. Electrons are stabilized/solvated with an increase in the moisture content (H(2)O/D(2)O) of seeds. The recombination of the trapped electron with radical cation gave intense thermoluminescence emission at 110 K. With the increase in temperature and the destruction of singlet, unmasking of an underlying heterogeneous population of free radicals was observed. These free radicals emanate mainly from the endosperm (approximately 95% by wt of the seed), whereas irradiated embryos show a broad multiplet of comparatively low amplitude. Radiolysis of carbohydrate, proteins (approximately 95% of endosperm), and lipids could possibly be responsible for the heterogeneous population of free radicals. Peroxyl radicals were also observed on annealing.

Nuclear fusion leads to chromosome doubling during mannitol pretreatment of barley (Hordeum vulgare L.) microspores

A cytological study of barley microspores during pretreatment of the uninucleate stage to the early culture stage was conducted utilizing six genotypes. Among the three main pretreatments investigated, microspores completed the first mitotic division during 28 d cold pretreatment of spikes, with or without leaf sheath attached, and during 0.3 M mannitol pretreatment of anthers at 25 degrees C. However, during a 4 d pretreatment in 0.3 M mannitol at 4 degrees C this first mitotic division was blocked or delayed and subsequently most often occurred during the first day on culture medium. The first mitotic division of most microspores pretreated in 0.3 M mannitol was mostly symmetrical (55-60%), whereas it was asymmetric (94%) during the 28 d cold pretreatment of spikes. Following the first mitotic division during the mannitol pretreatment at 25 degrees C, closely associated daughter nuclei often appeared to fuse via membrane coalescence, leading to a high frequency of large uninucleate microspores. Based upon nuclear size, the frequencies of fused uninucleate microspores in genotypes GBC 778, GBC 777 and Igri were estimated to be 87%, 54% and 75%, respectively, after a 4 d mannitol pretreatment at 25 degrees C. Chromosome numbers in dividing nuclei and relative densitometry measurements of nuclear DNA in microspores from cv. Igri confirmed the apparent fused nature of large nuclei in uninucleate microspores. The high frequency of fused nuclei indicates that nuclear fusion occurred between both symmetric and asymmetric nuclei. Microspores of cv. Igri cultured on filter paper following three different pretreatments provided an average of about 12 000 embryo-like structures (ELS) per plate. In samples, 85-97% of these ELS regenerated green shoots. The frequency of doubled haploids (74-83%) following all pretreatments was similar to the frequencies of fused nuclei. The pretreatment of spikes in 0.3 M mannitol at 4 degrees C for 4 d is preferred as it appears to provide genotype independent induction and suspension of nuclear division, as well as regenerating green plants in a shorter time than cold alone.