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Showing papers on "Endosperm published in 2002"


Journal ArticleDOI
12 Jul 2002-Cell
TL;DR: The authors isolated mutations in Arabidopsis to understand how the female gametophyte controls embryo and endosperm development and identified the DEMETER (DME) gene, which is required for maternal allele expression of the imprinted MEDEA (MEA) Polycomb gene in the central cell andendosperm.

740 citations


Journal ArticleDOI
TL;DR: A new model referred to as the "two-step branching and improper branch clearing model" is proposed to explain how amylopectin is synthesized, which emphasizes that two sets of reactions, alpha-1,6-branch formation and the subsequent alpha- 1,4-chain elongation, are fundamental to the construction of the cluster structure.
Abstract: Starch is made up of amylose (linear alpha-1,4-polyglucans) and amylopectin (alpha-1,6-branched polyglucans). Amylopectin has a distinct fine structure called multiple cluster structure and is synthesized by multiple subunits or isoforms of four classes of enzymes: ADPglucose pyrophosphorylase, soluble starch synthase (SS), starch branching enzyme (BE), and starch debranching enzyme (DBE). In the present paper, based on analyses of mutants and transgenic lines of rice in which each enzyme activity is affected, the contribution of the individual isoform to the fine structure of amylopectin in rice endosperm is evaluated, and a new model referred to as the "two-step branching and improper branch clearing model" is proposed to explain how amylopectin is synthesized. The model emphasizes that two sets of reactions, alpha-1,6-branch formation and the subsequent alpha-1,4-chain elongation, are catalyzed by distinct BE and SS isoforms, respectively, are fundamental to the construction of the cluster structure. The model also assesses the role of DBE, namely isoamylase or in addition pullulanase, to remove unnecessary alpha-1,6-glucosidic linkages that are occasionally formed at improper positions apart from two densely branched regions of the cluster.

481 citations


Journal ArticleDOI
TL;DR: A hypothesis is developed that trans-lycopene or a trans-allycopene derivative acts as an inductor in a kind of feedback mechanism stimulating endogenous carotenogenic genes in rice endosperm.
Abstract: To obtain a functioning provitamin A (beta-carotene) biosynthetic pathway in rice endosperm, we introduced in a single, combined transformation effort the cDNA coding for phytoene synthase (psy) and lycopene beta-cyclase (beta-lcy) both from Narcissus pseudonarcissus and both under the control of the endosperm-specific glutelin promoter together with a bacterial phytoene desaturase (crtI, from Erwinia uredovora under constitutive 35S promoter control). This combination covers the requirements for beta-carotene synthesis and, as hoped, yellow beta-carotene-bearing rice endosperm was obtained in the T(0)-generation. Additional experiments revealed that the presence of beta-lcy was not necessary, because psy and crtI alone were able to drive beta-carotene synthesis as well as the formation of further downstream xanthophylls. Plausible explanations for this finding are that these downstream enzymes are constitutively expressed in rice endosperm or are induced by the transformation, e.g., by enzymatically formed products. Results using N. pseudonarcissus as a model system led to the development of a hypothesis, our present working model, that trans-lycopene or a trans-lycopene derivative acts as an inductor in a kind of feedback mechanism stimulating endogenous carotenogenic genes. Various institutional arrangements for disseminating Golden Rice to research institutes in developing countries also are discussed.

387 citations


Journal ArticleDOI
TL;DR: Results indicate increased availability and utilization of resources in response to enhanced seed sink strength, increasing seed yield, and total plant biomass.
Abstract: Yield in cereals is a function of seed number and weight; both parameters are largely controlled by seed sink strength. The allosteric enzyme ADP-glucose pyrophosphorylase (AGP) plays a key role in regulating starch biosynthesis in cereal seeds and is likely the most important determinant of seed sink strength. Plant AGPs are heterotetrameric, consisting of two large and two small subunits. We transformed wheat (Triticum aestivum L.) with a modified form of the maize (Zea mays L.) Shrunken2 gene (Sh2r6hs), which encodes an altered AGP large subunit. The altered large subunit gives rise to a maize AGP heterotetramer with decreased sensitivity to its negative allosteric effector, orthophosphate, and more stable interactions between large and small subunits. The Sh2r6hs transgene was still functional after five generations in wheat. Developing seeds from Sh2r6hs transgenic wheat exhibited increased AGP activity in the presence of a range of orthophosphate concentrations in vitro. Transgenic Sh2r6hs wheat lines produced on average 38% more seed weight per plant. Total plant biomass was increased by 31% in Sh2r6hs plants. Results indicate increased availability and utilization of resources in response to enhanced seed sink strength, increasing seed yield, and total plant biomass.

293 citations


Journal ArticleDOI
TL;DR: It is proposed that DEK1 functions to maintain and restrict the aleurone cell fate imposed by CR4 through activation of its cysteine proteinase by contact with the outer endosperm surface.
Abstract: Endosperm of cereal grains is one of the most important renewable resources for food, feed, and industrial raw material. It consists of four triploid cell types, i.e., aleurone, starchy endosperm, transfer cells, and cells of the embryo surrounding region. In maize, the aleurone layer is one cell layer thick and covers most of the perimeter of the endosperm. Specification of maize aleurone cell fate is proposed to occur through activation of the tumor necrosis factor receptor-like receptor kinase CRINKLY4. A second maize gene essential for aleurone cell development is defective kernel 1 (dek1). Here we show that DEK1 shares high homology with animal calpains. The predicted 2,159-aa DEK1 protein has 21 transmembrane regions, an extracellular loop, and a cysteine proteinase domain that shares high homology with domain II of m-calpain from animals. We propose that DEK1 functions to maintain and restrict the aleurone cell fate imposed by CR4 through activation of its cysteine proteinase by contact with the outer endosperm surface. DEK1 seems to be the only member of the calpain superfamily in plants, Arabidopsis DEK1 sharing 70% overall identity with maize DEK1. The expression of dek1 in most plant tissues in maize and Arabidopsis, as well as its presence in a variety of higher plants, including angiosperms and gymnosperms, suggests that DEK1 plays a conserved role in plant signal transduction.

245 citations


Journal ArticleDOI
TL;DR: Two-dimensional gel electrophoresis is used for a time-resolved study of the changes in proteins that occur during seed development in barley and presents examples of proteins not previously experimentally observed, differential extractability of thiol-bound proteins, and possible allele-specific spot variation.
Abstract: In monocotyledonous plants, the process of seed development involves the deposition of reserves in the starchy endosperm and development of the embryo and aleurone layer. The final stages of seed development are accompanied by an increase in desiccation tolerance and drying out of the mature seed. We have used two-dimensional gel electrophoresis for a time-resolved study of the changes in proteins that occur during seed development in barley (Hordeum vulgare). About 1,000 low-salt extractable protein spots could be resolved on the two-dimensional gels. Protein spots were divided into six categories according to the timing of appearance or disappearance during the 5-week period of comparison. Nineteen different proteins or protein fragments in 36 selected spots were identified by matrix-assisted laser-desorption ionization time of flight mass spectrometry (MS) or nano-electrospray tandem MS/MS. Some proteins were present throughout development (for example, cytosolic malate dehydrogenase), whereas others were associated with the early grain filling (ascorbate peroxidase) or desiccation (Cor14b) stages. Most noticeably, the development process is characterized by an accumulation of low-M(r) alpha-amylase/trypsin inhibitors, serine protease inhibitors, and enzymes involved in protection against oxidative stress. We present examples of proteins not previously experimentally observed, differential extractability of thiol-bound proteins, and possible allele-specific spot variation. Our results both confirm and expand on knowledge gained from previous analyses of individual proteins involved in grain filling and maturation.

241 citations


Journal ArticleDOI
TL;DR: Uncooked and cooked sorghum showed improvement in in vitro protein digestibility as the structural complexity of the sample reduced from whole grain flour through endosperm flour to protein body-enriched samples, but this was not the case for maize.

227 citations


Journal ArticleDOI
TL;DR: Transient expression experiments in co-bombarded developing endosperms demonstrate that HvGAMYB trans-activates transcription from native Hor2 and Itr1 promoters through binding to the intact motifs described above.
Abstract: HvGAMYB, a MYB transcription factor previously shown to be expressed in barley aleurone cells in response to gibberellin during germination, also has an important role in gene regulation during endosperm development. The mRNA was detected early (10 DAF) in the seeds where it accumulates, not only in the aleurone layer, starchy endosperm, nucellar projection and vascular tissue, but also in the immature embryo as shown by in situ hybridization analysis. The HvGAMYB protein, expressed in bacteria, binds to oligonucleotides containing the 5'-TAACAAC-3' or 5'-CAACTAAC-3' sequences, derived from the promoter regions of the endosperm-specific genes Hor2 and Itr1, encoding a B-hordein and trypsin-inhibitor BTI-CMe, respectively. Binding is prevented when these motifs are mutated to 5'-TgACAAg-3' and 5'-CgACTgAC-3'. Transient expression experiments in co-bombarded developing endosperms demonstrate that HvGAMYB trans-activates transcription from native Hor2 and Itr1 promoters through binding to the intact motifs described above. Trans-activation of the Hor2 promoter also requires an intact prolamine box (PB). This suggests that HvGAMYB interacts in developing barley endosperms with the PB-binding factor BPBF, an endosperm-specific DOF transcriptional activator of the Hor2 gene. The in vivo interaction experiment between HvGAMYB and BPBF was done in the yeast two-hybrid system, where HvGAMYB potentiates the BPBF trans-activation capacity through interaction with its C-terminal domain.

215 citations


Journal ArticleDOI
TL;DR: The protein and amino acid composition, as well as the mRNA transcript profiles, of nearly isogenic inbred lines of W64A o1, o2, o5, o9, o11, Mucuronate, Defective endosperm B30, and fl2 were characterized.
Abstract: Maize starchy endosperm mutants have kernel phenotypes that include a brittle texture, susceptibility to insect pests, and inferior functional characteristics of products made from their flour. At least 18 such mutants have been identified, but only in the cases of opaque2 ( o2 ) and floury2 ( fl2 ), which affect different aspects of storage protein synthesis, is the molecular basis of the mutation known. To better understand the relationship between the phenotypes of these mutants and their biochemical bases, we characterized the protein and amino acid composition, as well as the mRNA transcript profiles, of nearly isogenic inbred lines of W64A o1 , o2 , o5 , o9 , o11 , Mucuronate ( Mc ), Defective endosperm B30 ( DeB30 ), and fl2 . The largest reductions in zein protein synthesis occur in the W64A o2 , DeB30 , and fl2 mutants, which have � 35 to 55% of the wild-type level of storage proteins. Zeins in W64A o5 , o9 , o11 , and Mc are within 80 to 90% of the amount found in the wild type. Only in the cases of o5 and Mc were significant qualitative changes in zein synthesis observed. The pattern of gene expression in normal and mutant genotypes was assayed by profiling endosperm mRNA transcripts at 18 days after pollination with an Affymetrix GeneChip containing � 1400 selected maize gene sequences. Compared with W64A sugary1 , a mutant defective in starch synthesis, alterations in the gene expression patterns of the opaque mutants are very pleiotropic. Increased expression of genes associated with physiological stress, and the unfolded protein response, are common features of the opaque mutants. Based on global patterns of

192 citations


Journal ArticleDOI
TL;DR: The results suggest that the cell number and cell division activity in rice endosperms are regulated by cytokinin levels in the endosperm and that root-derived Z + ZR play a pivotal role.

192 citations


Journal ArticleDOI
TL;DR: The structure of hard and soft wheat endosperm is discussed with particular emphasis on when differences inendosperm texture can be detected in the developing seed and the role of the puroindoline genes at the Ha locus is examined.

Journal ArticleDOI
TL;DR: It is described here that BPBF, a barley transcription factor of the DOF (DNA-Binding with One Finger) class, previously shown to be an activator of reserve protein encoding genes during development, also has a role in the control of hydrolase genes following seed germination.
Abstract: Functional analyses of a number of hydrolase gene promoters, induced by gibberellin (GA) in aleurone cells following germination, have identified a GA-responsive complex as a tripartite element containing a pyrimidine box motif 5'-CCTTTT-3'. We describe here that BPBF, a barley (Hordeum vulgare) transcription factor of the DOF (DNA-Binding with One Finger) class, previously shown to be an activator of reserve protein encoding genes during development, also has a role in the control of hydrolase genes following seed germination. Northern-blot, reverse transcriptase-polymerase chain reaction, and in situ hybridization analyses evidenced that the transcripts of the BPBF-encoding gene (Pbf), besides being present during endosperm development, are also expressed in aleurone cells of germinated seeds where they are induced by GA, an effect counteracted by abscisic acid. Electrophoretic mobility shift assays have shown that the BPBF protein binds specifically to the pyrimidine box motif in vitro within the different sequence contexts that naturally occur in the promoters of genes encoding a cathepsin B-like protease (Al21) and a low-isoelectric point alpha-amylase (Amy2/32b), both induced in the aleurone layers in response to GA. In transient expression experiments, BPBF repressed transcription of the Al21 promoter in GA-treated barley aleurone layers and reverted the GAMYB-mediated activation of this protease promoter.

Journal ArticleDOI
TL;DR: Mineral-accumulating compartments in developing seeds of Arabidopsis were studied using high-pressure-frozen/freeze-substituted samples and showed that Zn and Mn are mobilized from the endosperm to the embryo at different developmental stages, while studies of fertilized fis2 seeds, which hyperaccumulate Zn-phytate crystals in the chalazal vacuolar compartments, suggest that only the intact network is active in mineral
Abstract: Mineral-accumulating compartments in developing seeds of Arabidopsis were studied using high-pressure-frozen/freeze-substituted samples. Developing seeds store minerals in three locations: in the protein storage vacuoles of the embryo, and transiently in the endoplasmic reticulum (ER) and vacuolar compartments of the chalazal endosperm. Energy dispersive x-ray spectroscopy and enzyme treatments suggest that the minerals are stored as phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate) salts in all three compartments, although they differ in cation composition. Whereas embryo globoids contain Mg, K, and Ca as cations, the chalazal ER deposits show high levels of Mn, and the chalazal vacuolar deposits show high levels of Zn. The appearance of the first Zn-phytate crystals coincides with the formation of network-like extensions of the chalazal vacuoles. The core of these networks consists of a branched network of tubular ER membranes, which are separated from the delineating tonoplast membranes by a layer of cytosolic material. Degradation of the networks starts with the loss of the cytosol and is followed by the retraction of the ER, generating a network of collapsed tonoplast membranes that are resorbed. Studies of fertilized fis2 seeds, which hyperaccumulate Zn-phytate crystals in the chalazal vacuolar compartments, suggest that only the intact network is active in mineral sequestration. Mineral determination analysis and structural observations showed that Zn and Mn are mobilized from the endosperm to the embryo at different developmental stages. Thus, Zn appears to be removed from the endosperm at the late globular stage, and Mn stores appear to be removed at the late bent-cotyledon stage of embryo development. The disappearance of the Mn-phytate from the endosperm coincides with the accumulation of two major Mn binding proteins in the embryo, the 33-kD protein from the oxygen-evolving complex of photosystem II and the Mn superoxide dismutase. The possible functions of transient heavy metal storage in the chalazal endosperm are discussed. A model showing how phytic acid, a potentially cytotoxic molecule, is transported from its site of synthesis, the ER, to the different mineral storage sites is presented.

Journal ArticleDOI
TL;DR: It is determined that 3β-hydroxylase produced by OsGA3ox2 is important for the induction of RAmy1A expression and that the OsGA2ox1 product is not essential for α-amylase induction, and that active GA biosynthesis occurs in these two regions.
Abstract: We recently isolated two genes ( OsGA3ox1 and OsGA3ox2 ) from rice ( Oryza sativa ) encoding 3β-hydroxylase, which catalyzes the final step of active gibberellin (GA) biosynthesis (H. Itoh, M. Ueguchi-Tanaka, N. Sentoku, H. Kitano, M. Matsuoka, M. Kobayashi [2001] Proc Natl Acad Sci USA 98: 8909–8914). Using these cloned cDNAs, we analyzed the temporal and spatial expression patterns of the 3β-hydroxylase genes and also an α-amylase gene ( RAmy1A ) during rice seed germination to investigate the relationship between GA biosynthesis and α-amylase expression. Northern-blot analyses revealed that RAmy1A expression in the embryo occurs before the induction of 3β-hydroxylase expression, whereas in the endosperm, a high level of RAmy1A expression occurs 1 to 2 d after the peak of OsGA3ox2 expression and only in the absence of uniconazol. Based on the analysis of an OsGA3ox2 null mutant ( d18- Akibare dwarf), we determined that 3β-hydroxylase produced by OsGA3ox2 is important for the induction of RAmy1A expression and that the OsGA3ox1 product is not essential for α-amylase induction. The expression of OsGA3ox2 was localized to the shoot region and epithelium of the embryo, strongly suggesting that active GA biosynthesis occurs in these two regions. The synthesis of active GA in the epithelium is important for α-amylase expression in the endosperm, because an embryonic mutant defective in shoot formation, but which developed epithelium cells, induced α-amylase expression in the endosperm, whereas a mutant defective in epithelium development did not.

Journal ArticleDOI
TL;DR: Results suggest that the homologous sequence is not compensating for a lack of SBEI in sbe1::Mu mutants, and further study of this sBE1 mutation in the presence of other genetic mutations may help to understand the role of S BEI in determining starch structure in leaves and endosperm.
Abstract: Starch-branching enzymes (SBE) alter starch structure by breaking an α-1,4 linkage and attaching the reducing end of the new chain to a glucan chain by an α1,6 bond. In maize, three isoforms of SBE have been identified. In order to examine the function of the SBEI isoform, a reverse-genetics PCR-based screen was used to identify a mutant line segregating for a Mutator transposon within Sbe1. Compared to wild-type controls, Sbe1 transcripts accumulate at extremely low levels in leaves of the homozygous mutant. Antibodies failed to detect SBEI in leaf tissue of mutants or wild-type controls. In contrast, the level of SBEI in endosperm is undetectable in homozygous mutants while easily detected in wild-type controls. Starches extracted from mutant leaves and endosperm have structures indistinguishable from starches of wild-type controls as determined by size-exclusion chromatography (SEC) of intact starch and high-performance SEC of debranched starch. To investigate the possibility of compensation for the lack of SBEI by expression of the homologous sequence reported by Kim et al. (1998), a genomic fragment (Sbe1b) of this sequence was cloned. Northern hybridizations of mutant leaf, root, tassel, endosperm and embryo tissues with non-specific Sbe1b probes failed to reveal expression of the homologous sequence. These results suggest that the homologous sequence is not compensating for a lack of SBEI in sbe1::Mu mutants. Further study of this sbe1 mutation in the presence of other genetic mutations may help to understand the role of SBEI in determining starch structure in leaves and endosperm. Abbreviations: DAE, days after emergence; DAP, days after pollination; SBE, starch-branching enzyme

Journal ArticleDOI
TL;DR: Greenhouse resistance tests indicated that the accumulation of FsTRI101-encoded acetyltransferase in this plant confers partial protection against the spread of F. graminearum in inoculated wheat heads (spikes).
Abstract: Fusarium head blight occurs in cereals throughout the world and is especially important in humid growing regions. Fusarium head blight (FHB) has re-emerged as a major disease of wheat and barley in the U.S. and Canada since 1993. The primary causal agents of FHB, Fusarium graminearum and Fusarium culmorum, can produce deoxynivalenol (DON), a trichothecene mycotoxin that enhances disease severity and poses a health hazard to humans and monogastric animals. To reduce the effects of DON on wheat, we have introduced FsTRI101, a Fusarium sporotrichioides gene formerly known as TriR, into the regenerable cultivar Bobwhite. TRI101 encodes an enzyme that transfers an acetyl moiety to the C3 hydroxyl group of trichothecenes. Four different transgenic plants carrying the FsTRI101 gene were identified. Although expression levels varied among the four lines, all of them accumulated FsTRI101 transcripts in endosperm and glume. TRI101-encoded acetyltransferase activity was detected in endosperm extracts of a single plant that accumulated FsTRI101 mRNA. Greenhouse resistance tests indicated that the accumulation of FsTRI101-encoded acetyltransferase in this plant confers partial protection against the spread of F. graminearum in inoculated wheat heads (spikes).

Journal ArticleDOI
TL;DR: It is shown that the pinB-D1b alteration, common in hard textured wheats, can be complemented by the expression of wild-type pinB -D1a in transformed plants, indicating that thePinB-C1a alteration is most likely the causative Ha mutation in the majority of hard wheats.
Abstract: Wheat grain hardness is a major factor in the wheat end-product quality. Grain hardness in wheat affects such parameters as milling yield, starch damage and baking properties. A single locus determines whether wheat is hard or soft textured. This locus, termed Hardness (Ha), resides on the short arm of chromosome 5D. Sequence alterations in the tryptophan-rich proteins puroindoline a and b (PINA and PINB) are inseparably linked to hard textured grain, but their role in endosperm texture has been controversial. Here, we show that the pinB-D1b alteration, common in hard textured wheats, can be complemented by the expression of wild-type pinB-D1a in transformed plants. Transgenic wheat seeds expressing wild-type pinB were soft in phenotype, having greatly increased friabilin levels, and greatly decreased kernel hardness and damaged starch. These results indicate that the pinB-D1b alteration is most likely the causative Ha mutation in the majority of hard wheats.

Journal ArticleDOI
31 Jan 2002-Nature
TL;DR: It is shown that diploid endosperms are common among early angiosperm lineages and may represent the ancestral condition among flowering plants.
Abstract: In flowering plants, the developmental and genetic basis for the establishment of an embryo-nourishing tissue differs from all other lineages of seed plants. Among extant nonflowering seed plants (conifers, cycads, Ginkgo, Gnetales), a maternally derived haploid tissue (female gametophyte) is responsible for the acquisition of nutrients from the maternal diploid plant, and the ultimate provisioning of the embryo. In flowering plants, a second fertilization event, contemporaneous with the fusion of sperm and egg to yield a zygote, initiates a genetically biparental and typically triploid embryo-nourishing tissue called endosperm. For over a century, triploid biparental endosperm has been viewed as the ancestral condition in extant flowering plants. Here we report diploid biparental endosperm in Nuphar polysepalum, a basal angiosperm. We show that diploid endosperms are common among early angiosperm lineages and may represent the ancestral condition among flowering plants. If diploid endosperm is plesiomorphic, the triploid endosperms of the vast majority of flowering plants must have evolved from a diploid condition through the developmental modification of the unique fertilization process that initiates endosperm.

Journal ArticleDOI
TL;DR: The growing zone of maize seedling primary roots accumulates proline at low water potential and the endosperm is the source of the proline that accumulates in the root tips of intact seedlings.

Journal ArticleDOI
TL;DR: In maize, cells at the base of the endosperm are transformed into transfer cells that facilitate nutrient uptake by the developing seed and ZmMRP-1 is the first transfer cell–specific transcriptional activator to be identified.
Abstract: In maize, cells at the base of the endosperm are transformed into transfer cells that facilitate nutrient uptake by the developing seed. ZmMRP-1 is the first transfer cell-specific transcriptional activator to be identified. The protein it encodes contains nuclear localization signals and a MYB-related DNA binding domain. A single gene copy is present in maize, mapping to a locus on chromosome 8. ZmMRP-1 is first expressed soon after fertilization, when the endosperm is still a multinuclear coenocyte. The transcript accumulates in the basal nucleocytoplasmic domain that gives rise to transfer cells after cellularization. The transcript can be detected throughout transfer cell development, but it is not found in mature cells. ZmMRP-1 strongly transactivates the promoters of two unrelated transfer cell-specific genes. The properties of ZmMRP-1 are consistent with it being a determinant of transfer cell-specific expression. Possible roles for ZmMRP-1 in the regulation of endosperm and transfer cell differentiation are discussed.

Journal ArticleDOI
TL;DR: The temporal, spatial and hormonal regulation pattern of LeXET4 gene expression suggests that XET has a role in endosperm cap weakening, a key process regulating tomato seed germination.
Abstract: Xyloglucan endotransglycosylases (XETs) modify xyloglucans, major components of primary cell walls in dicots. A cDNA encoding an XET (LeXET4) was isolated from a germinating tomato (Lycopersicon esculentum Mill.) seed cDNA library. DNA gel blot analysis showed that LeXET4 is a single-copy gene in the tomato genome. LeXET4 mRNA was strongly expressed in germinating seeds, was much less abundant in stems, and was not detected in roots, leaves or flower tissues. During germination, LeXET4 mRNA was detected in seeds within 12 h of imbibition with maximum mRNA abundance at 24 h. Tissue prints showed that LeXET4 mRNA was localized exclusively to the endosperm cap region. Expression of LeXET4 was dependent on exogenous gibberellin (GA) in GA-deficient (gib-1 mutant) tomato seeds, while abscisic acid, a seed germination inhibitor, had no effect on LeXET4 mRNA expression in wild-type seeds. LeXET4 mRNA disappeared after radicle emergence, even though degradation of the lateral endosperm cell walls continued. The temporal, spatial and hormonal regulation pattern of LeXET4 gene expression suggests that XET has a role in endosperm cap weakening, a key process regulating tomato seed germination.

Journal ArticleDOI
TL;DR: The dek1 gene product appears to control different cellular-developmental processes depending on cellular context, and functions in embryonic pattern formation, cell fate specification and pattern formation in the leaf epidermis, andcell fate specification in the endosperm.
Abstract: Mutants in the maize defective kernel1 (dek1) gene are blocked in embryogenesis and the endosperm is chalky and lacks an aleurone layer. Here we show that intermediate alleles result in embryos that lack a shoot axis while weak alleles result in endosperms with mosaic aleurone and deformed plants with epidermal cells that resemble bulliform cells, a specialized epidermal cell type. This indicates that dek1 functions in embryonic pattern formation, cell fate specification and pattern formation in the leaf epidermis, and cell fate specification in the endosperm. Thus, the dek1 gene product appears to control different cellular-developmental processes depending on cellular context. The phenotype of the weak dek1-Dooner allele resembles the crinkly4 (cr4) mutant phenotype. Double mutants between dek1 and cr4 showed elements of epistasis, additivity and synergy, suggesting that the gene products may function in overlapping developmental processes. cr4 transcript was detectable in dek1 mutant kernels indicating that DEK1 was not required for Cr4 transcript accumulation. To test whether DEK1 regulated the ligand for the CR4 receptor kinase, a genetic mosaic analysis was performed. The dek1 phenotype appeared to be generally cell-autonomous, leading to the conclusion that it was not likely to produce a diffusible signal molecule, and therefore was not likely to regulate the CR4 ligand. SUMMARY

Journal ArticleDOI
TL;DR: Two further families of waxy cultivars have no detectable amylose in the endosperm starch and were selected in the 20th century from chemically mutagenized populations of wild-type barley because of alterations in the GBSSI gene.
Abstract: Reasons for the variable amylose content of endosperm starch from waxy cultivars of barley (Hordeum vulgare) were investigated. The mature grains of most such cultivars contain some amylose, although amounts are much lower than in wild-type cultivars. In these low-amylose cultivars, amylose synthesis starts relatively late in grain development. Starch granules in the outer cell layers of the endosperm contain more amylose than those in the center. This distribution corresponds to that of granule-bound starch synthase I (GBSSI), which is more severely reduced in amount in the center of the endosperm than in the outer cell layers, relative to wild-type cultivars. A second GBSSI in the barley plant, GBSSIb, is not detectable in the endosperm and cannot account for amylose synthesis in the low-amylose cultivars. The change in the expression of GBSSI in the endosperm of the low-amylose cultivars appears to be due to a 413-bp deletion of part of the promoter and 5'-untranslated region of the gene. Although these cultivars are of diverse geographical origin, all carry this same deletion, suggesting that the low-amylose cultivars have a common waxy ancestor. Records suggest a probable source in China, first recorded in the 16th century. Two further families of waxy cultivars have no detectable amylose in the endosperm starch. These amylose-free cultivars were selected in the 20th century from chemically mutagenized populations of wild-type barley. In both cases, 1-bp alterations in the GBSSI gene completely eliminate GBSSI activity.

Journal ArticleDOI
TL;DR: In vivo observations show that, as in cytokinesis, cellularisation of the Arabidopsis endosperm is coupled to nuclear division, and imply that cellularisation and cytokineis share multiple components of the same basic machinery.
Abstract: Distinct forms of cytokinesis characterise specific phases of development in plants. In Arabidopsis, as in many other species, the endosperm that nurtures the embryo in the seed initially develops as a syncytium. This syncytial phase ends with simultaneous partitioning of the multinucleate cytoplasm into individual cells, a process referred to as cellularisation. Our in vivo observations show that, as in cytokinesis, cellularisation of the Arabidopsis endosperm is coupled to nuclear division. A genetic analysis reveals that most Arabidopsis mutations affecting cytokinesis in the embryo also impair endosperm cellularisation. These results imply that cellularisation and cytokinesis share multiple components of the same basic machinery. We further report the identification of mutations in a novel gene, SPATZLE, that specifically interfere with cellularisation of the endosperm, but not with cytokinesis in the embryo. The analysis of this mutant might identify a specific checkpoint for the onset of cellularisation.

Journal ArticleDOI
TL;DR: The evolutionary origin of double fertilization and the resultant endosperm tissue in flowering plants remains a puzzle, despite over a century of research, but the recent resurgence of approaches to evolutionary developmental biology combining comparative biology with phylogenetics provides new understanding.
Abstract: The evolutionary origin of double fertilization and the resultant endosperm tissue in flowering plants remains a puzzle, despite over a century of research. The recent resurgence of approaches to evolutionary developmental biology combining comparative biology with phylogenetics provides new understanding of endosperm origins.

Journal ArticleDOI
TL;DR: In this article, the fracture properties of small cylindrical samples of endosperm machined from single kernels of several varieties of wheat were measured using three methods: compression, wedge fracture and indentation.

Journal ArticleDOI
TL;DR: Protein quality and endosperm modification score were always within expected values for QPM and tryptophan concentration in protein was the most stable trait, followed by protein concentration in grain, then endos perm modification score and finally grain yield.
Abstract: Quality protein maize (Zea mays L.) (QPM) can help alleviate human malnutrition and reduce costs of animal feed because it contains the opaque-2 mutation, which results in increased lysine and tryptophan concentrations and a higher biological value as a food than normal maize. To be commercially successful, however, QPM cultivars must be agronomically competitive with normal-endosperm alternatives while consistently achieving expected protein quality and endosperm modification (i.e., translucent or near-normal phenotype) standards. To assess stability of grain yield, protein content and quality, and endosperm modification of QPM cultivars, we evaluated 18 single-cross, 18 three-way, and 18 double-cross hybrids, and eight open-pollinated cultivars (OPCs) grown at 13 tropical locations on four continents. Hybrids averaged 13% higher grain yield than OPCs (5.97 and 5.17 Mg ha -1 ), whereas protein concentration in grain was 2% greater for the OPC relative to hybrid cultivars (94.6 and 92.4 g kg -1 ). Endosperm modification score and tryptophan concentration in protein were similar for all cultivar types. Genotype × environment interactions and sums of squares for deviations from linear regression (S 2 d ) for grain yield and protein concentration in grain were largest (indicating least stability) for single-cross hybrids, followed by three-way, double-cross, and open-pollinated cultivars (OPCs), successively. The reverse trend was observed for endosperm modification score, suggesting that more homogeneous cultivars had greater stability for this trait. Additive main effects and multiplicative interactions (AMMI) analysis indicated that genotype × environment interaction effects for grain yield and endosperm modification score were different for hybrids than OPCs; certain environments favored either hybrids or OPCs. In conclusion (i) protein quality and endosperm modification score were always within expected values for QPM and (ii) tryptophan concentration in protein was the most stable trait, followed by protein concentration in grain, then endosperm modification score and finally grain yield.

Journal ArticleDOI
TL;DR: H2O2 was formed at the expense of NADH only in the presence of Mn2+ and dinitrophenol by the extract from the micropylar endosperm in which peroxidase activity was present.
Abstract: Peroxidase activity developed specifically in the micropylar region of the endosperm of imbibed tomato seeds prior to radicle emergence. The activity was first detected approximately 24 h after the start of imibibition (6 h before radicle emergence) and increased markedly thereafter. In the lateral portion of the endosperm, peroxidase activity was undetectable for the first 2 d after the start of imbibition. Although the activity in the lateral endosperm became detectable 3 d after imbibition, the extent of the development of the activity was slight. The localization of peroxidase activity in the micropylar endosperm 2 d after the start of imbibition was confirmed by tissue printing analyses. When the endosperm tissues were wounded, there was an enhancement of the enzyme activity at the wounded region. H2O2 was formed at the expense of NADH only in the presence of Mn2+ and dinitrophenol by the extract from the micropylar endosperm in which peroxidase activity was present. The presence of H2O2 in the micropylar portion of the endosperm was shown histochemically. The possible functions of the peroxidases that develop in the endosperm of tomato seeds are discussed.

Journal ArticleDOI
TL;DR: 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 α-amylase released by the aleurone.
Abstract: Homozygous lines of barley overexpressing a wheat thioredoxin h transgene (up to 30-fold) were generated earlier by using a B1-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 α-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 α-amylase activity with a 1.6- to 2.8-fold increase in gibberellin A1 (GA1) content; (ii) a similar acceleration in the appearance of the α-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 α-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 α-amylase released by the aleurone.

01 Jan 2002
TL;DR: Four additional TTN genes are identified and a general model for the titan phenotype is presented, which can result from disruption of chromosome dynamics or microtubule function (ttn1 and ttn5), and three other genes have been identified that affect endosperm nuclear morphology.
Abstract: The titan mutants of Arabidopsis exhibit striking defects in seed development. The defining feature is the presence of abnormal endosperm with giant polyploid nuclei. Several TTN genes encode structural maintenance of chromosome proteins (condensins and cohesins) required for chromosome function at mitosis. Another TTN gene product (TTN5) is related to the ARL2 class of GTP-binding proteins. Here, we identify four additional TTN genes and present a general model for the titan phenotype. TTN1 was cloned after two tagged alleles were identified through a large-scale screen of T-DNA insertion lines. The predicted gene product is related to tubulin-folding cofactor D, which interacts with ARL2 in fission yeast (Schizosaccharomyces pombe) and humans to regulate tubulin dynamics. We propose that TTN5 and TTN1 function in a similar manner to regulate microtubule function in seed development. The titan phenotype can therefore result from disruption of chromosome dynamics (ttn3, ttn7, and ttn8) or microtubule function (ttn1 and ttn5). Three other genes have been identified that affect endosperm nuclear morphology. TTN4 and TTN9 appear to encode plant-specific proteins of unknown function. TTN6 is related to the isopeptidase T class of deubiquitinating enzymes that recycle polyubiquitin chains following protein degradation. Disruption of this gene may reduce the stability of the structural maintenance of chromosome complex. Further analysis of the TITAN network should help to elucidate the regulation of microtubule function and chromosome dynamics in seed development. Seed development in Arabidopsis requires coordinated differentiation of the embryo proper, suspensor, endosperm tissue, and seed coat. Interactions between these components have been explored in part through the analysis of embryo-defective mutants (Meinke, 1995). Some of these mutants have