SEARCH · PubMed Health

Results for “Endosperm”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2006

Identification of QTL and association of a phytoene synthase gene with endosperm colour in durum wheat.

The yellow colour of durum wheat (Triticum turgidum L. var durum) semolina is due in part to the presence of carotenoid pigments found in the endosperm and is an important end-use quality trait. We hypothesized that variation in the genes coding for phytoene synthase (Psy), a critical enzyme in carotenoid biosynthesis, may partially explain the phenotypic variation in endosperm colour observed among durum cultivars. Using rice sequence information, primers were designed to PCR clone and sequence the Psy genes from Kofa (high colour) and W9262-260D3 (medium colour) durum cultivars. Sequencing confirmed the presence of four Psy genes in each parent, corresponding to a two member gene family designated as Psy1-1, Psy1-2 and Psy2-1 and Psy2-2. A genetic map was constructed using 155 F1-derived doubled haploid lines from the cross W9262-260D3/Kofa with 194 simple sequence repeat and DArT markers. Using Psy1-1 and Psy2-1 allele-specific markers and chromosome mapping, the Psy1 and Psy2 genes were located to the group 7 and 5 chromosomes, respectively. Four quantitative trait loci (QTL) underlying phenotypic variation in endosperm colour were identified on chromosomes 2A, 4B, 6B, and 7B. The Psy1-1 locus co-segregated with the 7B QTL, demonstrating an association of this gene with phenotypic variation for endosperm colour. This work is the first report of mapping Psy genes and supports the role of Psy1-1 in elevated levels of endosperm colour in durum wheat. This gene is a target for the further development of a molecular marker to enhance selection for endosperm colour in durum wheat breeding programs.

Alkyl and Aryl Transferases↗

PubMed2002

Seed yield and plant biomass increases in rice are conferred by deregulation of endosperm ADP-glucose pyrophosphorylase.

In this work we test the hypothesis that yield of rice ( Oryza sativa L.) can be enhanced by increasing endosperm activity of ADP-glucose pyrophosphorylase (AGP), a key enzyme in starch biosynthesis. The potential for increases in yield exist because rice initiates more seeds than are taken to maturity and possesses excess photosynthetic capacity that could be utilized if there were more demand for assimilate. Following an approach already shown to be successful in wheat, experiments were designed to increase demand for assimilate by increasing the capacity for starch synthesis in endosperm. This was accomplished by transforming rice with a modified maize AGP large subunit sequence ( Sh2r6hs) under control of an endosperm-specific promoter. This altered subunit confers upon AGP decreased sensitivity to allosteric inhibition by inorganic phosphate (Pi) and enhanced heat stability, potentially leading to higher AGP activity in vivo. The Sh2r6hs transgene increased AGP activity in developing endosperm by 2.7-fold in the presence of Pi. Increases in AGP activity in transgenic seeds compared with controls were maximal between 10-15 days after anthesis. Starch content of individual seeds at harvest was not increased, but seed weight per plant and total plant biomass were each increased by more than 20%. Increased endosperm AGP activity thus stimulates setting of additional seeds and overall plant growth rather than increasing yield of seeds already set. Results demonstrate that deregulation of endosperm AGP increases overall plant sink strength, leading to larger, more productive plants in a manner similar to that in wheat having similar genetic modification.

Biomass↗

PubMed2003

Relative turnover numbers of maize endosperm and potato tuber ADP-glucose pyrophosphorylases in the absence and presence of 3-phosphoglyceric acid.

Adenosine diphosphate glucose pyrophosphorylase (AGPase; EC 2.7.7.27) synthesizes the starch precursor, ADP-glucose. It is a rate-limiting enzyme in starch biosynthesis and its activation by 3-phosphoglyceric acid (3PGA) and/or inhibition by inorganic phosphate (Pi) are believed to be physiologically important. Leaf, tuber and cereal embryo AGPases are highly sensitive to these effectors, whereas endosperm AGPases are much less responsive. Two hypotheses can explain the 3PGA activation differences. Compared to leaf AGPases, endosperm AGPases (i) lack the marked ability to be activated by 3PGA or (ii) they are less dependent on 3PGA for activity. The absence of purified preparations has heretofore negated answering this question. To resolve this issue, heterotetrameric maize ( Zea mays L.) endosperm and potato ( Solanum tuberosum L.) tuber AGPases expressed in Escherichia coli were isolated and the relative amounts of enzyme protein were measured by reaction to antibodies against a motif resident in both small subunits. Resulting reaction rates of both AGPases are comparable in the presence but not in the absence of 3PGA when expressed on an active-protein basis. We also placed the potato tuber UpReg1 mutation into the maize AGPase. This mutation greatly enhances 3PGA sensitivity of the potato AGPase but it has little effect on the maize AGPase. Thirdly, lysines known to bind 3PGA in potato tuber AGPase, but missing from the maize endosperm AGPase, were introduced into the maize enzyme. These had minimal effect on maize endosperm activity. In conclusion, the maize endosperm AGPase is not nearly as dependent on 3PGA for activity as is the potato tuber AGPase.

Enzyme Activation↗

PubMed2005

Genetic control of cell wall invertases in developing endosperm of maize.

We show here that the total invertase activity in developing seeds of maize is due to two cell wall invertase (CWI) genes, Incw1 and Incw2 (Mn1). Our previous results have shown that loss-of-function mutations at the Mn1 locus lead to the miniature-1 (mn1) seed phenotype, marked by a loss of >70% of seed weight at maturity. The mn1 seed mutant is, however, non-lethal presumably because it retains a residual low level, approximately 1%, of the total CWI activity relative to the Mn1 endosperm throughout seed development. Evidence here shows that the residual activity in the mn1 mutant is encoded by the Incw1 gene. RNA level analyses, especially quantitative real-time PCR studies, showed significant spatial and temporal heterogeneity in the expression of the two CWI genes in the developing endosperm. The Mn1-encoded Incw2 transcripts were seen at the highest levels in the basal region (the sugar unloading zone) during the early phase of cell division and elongation in the endosperm. In contrast, the highest levels of Incw1 transcripts were seen in the storage phase in both the upper (storage cells) and the lower parts of the endosperm. Protein and enzyme level analyses, however, appeared to show a lack of concordance with the RNA level of expression in both the Mn1 and mn1 endosperms, indicating a possibility of post-transcriptional control in the expression of these two genes. Collectively, the data suggest an important role for apoplastic cleavage of sucrose throughout the duration of seed development; and, of the two isoforms, the INCW2 appears to control metabolic flux of sugar utilization in the developing endosperm.

Cell Wall↗

PubMed2005

Endosperm-preferred expression of maize genes as revealed by transcriptome-wide analysis of expressed sequence tags.

The transcriptome-wide endosperm-preferred expression of maize genes was addressed by analyzing a large database of expressed sequence tags (ESTs). We generated 30,531 high quality sequence-reads from the 5'-ends of cDNA libraries from maize endosperm harvested at 10, 15, and 20 days after pollination. A further 196,900 maize sequence-reads retrieved from public databases were added to this endosperm collection to generate MAIZEST, a database with tools for data storage and analysis. MAIZEST contains 227,431 ESTs, one third of which represents developing endosperm and the remaining two-thirds represent transcripts from 49 cDNA libraries constructed from different organs and tissues. Assembling the MAIZEST ESTs generated 29,206 putative transcripts, of which a set of 4032 assembled sequences was composed exclusively of sequences derived from endosperm cDNA libraries. After sequence analysis using overlapping parameters, a sub-set of 2403 assembled sequences was functionally annotated and revealed a wide variety of putative new genes involved in endosperm development and metabolism.

Expressed Sequence Tags↗

PubMed2005

Effect of the opaque and floury mutations on the accumulation of dry matter and protein fractions in maize endosperm.

Grains of nine opaque (o) and floury (fl) mutants of maize (Oh43o1, Oh43o2, B79o5, B37o7, W22o10, W22o11, W22o13, Oh43fl1 and Oh43fl2) were examined for the weight proportions of their component tissues and the content of eight nitrogen fractions in their endosperms. A linear regression was found connecting the amounts (mg per endosperm) of zeins and true proteins (crude proteins minus non-protein nitrogen) for the non-opaque2 mutants. The data points connecting zeins to true proteins present in the mature endosperms of six wild-type (+) inbred lines and their o2 versions were located outside (+) or within (o2) the 95% confidence range of the regression line. The data obtained from the developing and mature endosperms of the W22o7 inbred line (Di Fonzo et al., Plant Sci. Lett., 1979, 77) and the floury portion of mature endosperms of three other wild-type inbred lines fell practically on the regression line. The effects of genotype and environmental factors upon the relative accumulation rate of zeins were assessed from the present results and the data taken from the literature concerning the quantitative interdependence between zeins and true proteins in immature and mature endosperms.

Gene Expression Regulation, Plant↗

PubMed2000

Regulation of programmed cell death in maize endosperm by abscisic acid.

Cereal endosperm undergoes programmed cell death (PCD) during its development, a process that is controlled, in part, by ethylene. Whether other hormones influence endosperm PCD has not been investigated. Abscisic acid (ABA) plays an essential role during late seed development that enables an embryo to survive desiccation. To examine whether ABA is also involved in regulating the onset of PCD during endosperm development, we have used genetic and biochemical means to disrupt ABA biosynthesis or perception during maize kernel development. The onset and progression of cell death, as determined by viability staining and the appearance of internucleosomal DNA fragmentation, was accelerated in developing endosperm of ABA-insensitive vp1 and ABA-deficient vp9 mutants. Ethylene was synthesized in vp1 and vp9 mutant kernels at levels that were 2-4-fold higher than in wild-type kernels. Moreover, the increase and timing of ethylene production correlated with the premature onset and accelerated progression of internucleosomal fragmentation in these mutants. Treatment of developing wild-type endosperm with fluridone, an inhibitor of ABA biosynthesis, recapitulated the increase in ethylene production and accelerated execution of the PCD program that was observed in the ABA mutant kernels. These data suggest that a balance between ABA and ethylene establishes the appropriate onset and progression of programmed cell death during maize endosperm development.

Abscisic Acid↗

PubMed2002

The GAMYB protein from barley interacts with the DOF transcription factor BPBF and activates endosperm-specific genes during seed development.

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.

Base Sequence↗

PubMed1997

Nitrogen and hormonal responsiveness of the 22 kDa alpha-zein and b-32 genes in maize endosperm is displayed in the absence of the transcriptional regulator Opaque-2.

The maize (Zea mays L.) b-ZIP transcriptional activator Opaque-2(O2) regulates the synthesis of major endosperm proteins. In the o2 homozygote, 22 kDa zein prolamins and the b-32 ribosome-inactivating protein are greatly reduced in level. An in vitro endosperm culture system has been studied in which o2 endosperm synthesizes 22 kDa zein and b-32 in response to nitrogen supplements. An increase in 22 kDa zein mRNA concentration is also seen, implying an effect at the level of transcription or differential RNA turnover. The nitrogen-dependent induction of 22 kDa zein synthesis in cultured o2 endosperm was further investigated by analysing transient expression of reporter constructs. The highest response to nitrogen was exhibited by the intact 22 kDa zein promoter. Removal of individual O2 binding sites either reduced or increased overall promoter activity, but always decreased the nitrogen-dependent stimulation of activity. This effect was observed equally in wild-type and o2 mutant endosperm. It is concluded that a factor other then O2 is responsible for activating the 22 kDa zein promoter under high-nitrogen culture conditions. Despite its occurrence in the absence of O2 protein, the nitrogen response is mediated through binding at O2 binding sites. An induction of 22 kDa zein and b-32 synthesis in cultured o2 endosperm could also be achieved on nitrogen-free media by the addition of abscisic acid or methyl jasmonate.

Abscisic Acid↗

PubMed2000

rgf1, a mutation reducing grain filling in maize through effects on basal endosperm and pedicel development.

The maize cob presents an excellent opportunity to screen visually for mutations affecting assimilate partitioning in the developing kernel. We have identified a defective kernel mutant termed rgf1, reduced grain filling, with a final grain weight 30% of the wild type. In contrast with most defective endosperm mutants, rgf1 shows gene dosage-dependent expression in the endosperm. rgf1 kernels possess a small endosperm incompletely filling the papery pericarp, but embryo development is unaffected and the seeds are viable. The mutation conditions defective pedicel development and greatly reduces expression of endosperm transfer layer-specific markers. rgf1 exhibits striking morphological similarities to the mn1 mutant, but maps to a locus approximately 4 cM away from mn1 on chromosome 2 of maize. Despite reduced starch accumulation in the mutant, no obvious lesion in starch biosynthesis has been detected. Free sugar levels are unaltered in rgf1 endosperm. Rates of sugar uptake, measured over short (8 h) periods in cultured kernels, are increased in rgf1 compared to the wild type. rgf1 and wild-type kernels, excised at 5 DAP and cultured in vitro also develop differently in response to variations in sugar regime: glucose concentrations above 1% arrest placentochalazal development of rgf1 kernels, but have no effect on cultured wild-type kernels. These findings suggest that either uptake or perception of sugar(s) in endosperm cells at 5-10 DAP determines the rgf1 kernel phenotype.

Base Sequence↗

PubMed2003

Genome-wide mRNA profiling reveals heterochronic allelic variation and a new imprinted gene in hybrid maize endosperm.

We have taken a genomic approach to examine global gene expression in the maize endosperm in relation to dosage and parental effects. Endosperm of eight hybrids generated by reciprocal crosses and their seven inbred parents were sampled at three developmental stages: 10, 14, and 21 days after pollination (DAP). These samples were subjected to GeneCalling, an open-ended mRNA-profiling technology, which simultaneously analyzes thousands of genes. Results indicated that the overall level of gene expression in the maize endosperm was dosage-dependent, that is, the gene expression was proportional to the parental genome contribution of 2n maternal : 1n paternal. However, approximately 8% of the genes deviated from such allelic additive expression and exhibited differential expression in hybrids of reciprocal crosses, resembling either maternally or paternally expressed genes. There were more genes with maternal-like expression (MLE) than those with paternal-like expression (PLE). Allele-specific expression analysis of four selected genes using the WAVE denaturing HPLC (dHPLC) system revealed several mechanisms responsible for the deviation from the allelic additive expression in the hybrid endosperm: heterochronic allelic variation, allelic variation in the level of expression, and genomic imprinting. We discovered a novel imprinted gene no-apical-meristem (NAM) related protein1 (nrp1) that was expressed only in the endosperm and regulated by gene-specific imprinting. The nrp1 gene, a putative transcriptional factor, may play an important role in endosperm development.

Alleles↗

PubMed1995

Organismal duplication, inclusive fitness theory, and altruism: understanding the evolution of endosperm and the angiosperm reproductive syndrome.

For almost a century, events relating to the evolutionary origin of endosperm, a unique embryo-nourishing tissue that is essential to the reproductive process in flowering plants, have remained a mystery. Integration of recent advances in phylogenetic reconstruction, comparative reproductive biology, and genetic theory can be used to elucidate the evolutionary events and forces associated with the establishment of endosperm. Endosperm is shown to be derived from one of two embryos formed during a rudimentary process of "double fertilization" that evolved in the ancestors of angiosperms. Acquisition of embryo-nourishing behavior (with accompanying loss of individual fitness) by this supernumerary fertilization product was dependent upon compensatory gains in the inclusive fitness of related embryos. The result of the loss of individual fitness by one of the two original products of double fertilization was the establishment of endosperm, a highly modified embryo/organism that reproduces cryptically through behavior that enhances the fitness of its associated embryo within a seed. Finally, although triploid endosperm remains a synapomorphy of angiosperms, inclusive fitness analysis demonstrates that the embryo-nourishing properties of endosperm initially evolved in a diploid condition.

Journal Article↗

PubMed2000

Is The Barley Endosperm a Water Reservoir for the Embryo When Germinating Seeds Are Dried?

The water content of germinating seeds fluctuates in response to water potential changes in the surrounding environment. We tested the hypothesis that the endosperm functions as a water reservoir when imbibed seeds experience drying, and we characterized water uptake and movement within barley (Hordeum vulgare cv. Triumph) caryopses (hereafter referred to as seeds). Water movement into and through germinating barley seeds during imbibition and drying was determined gravimetrically and with the fluorescent dye trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate (PTS). During imbibition, embryo tissues hydrated more rapidly and reached a higher water content (g H20/g dry weight) than did the endosperm, although the endosperm eventually contained nine times as much total water. When barley seeds that had imbibed for 12 h were exposed to moderate (-4 MPa) drying, PTS solution moved from the endosperm into the shoot meristem, radicle, and scutellum, but not vice versa. Radicle emergence and elongation proceeded for up to 8 h. With harsh (-150 MPa) drying, PTS concentrated almost exclusively in the radicle. These data illustrate that the endosperm is at least a temporary water storage compartment external to the embryo itself. We speculate that water supplied by the endosperm may be important in reducing the harmful effects of drying during the critical transition period when a germinating seed changes from a desiccation-tolerant to a desiccation-intolerant organism.

Journal Article↗

PubMed2003

Isolation of GUS marker lines for genes expressed in Arabidopsis endosperm, embryo and maternal tissues.

In order to identify marker lines expressing GUS in various endosperm compartments and at different developmental stages, a collection of Arabidopsis thaliana (L.) Heynh. promoter trap lines were screened. The screen identified 16 lines displaying GUS-reporter gene expression in the endosperm, embryo and other seed organs. The distinctive patterns of GUS expression in these lines provide molecular markers for most cell compartments in the endosperm of Arabidopsis seeds at all developmental stages, and represent a valuable research tool for characterizing present and future Arabidopsis seed mutants. GUS expression patterns of these 16 lines are presented here. One line showed chalazal endosperm-specific GUS activity at the heart stage of embryo development. In six lines embryo-specific GUS activity was detected. Six lines exhibited GUS activity predominantly in the endosperm and embryo while two lines showed strong GUS activity in all seed organs. In one line GUS activity was detected in integuments and syncytial endosperm, while the GUS activity at the cotyledonary stage of the embryo was seed coat-specific. In addition, two funiculus markers and two silique markers expressed in the abscission zone and the guard cells are also presented.

Arabidopsis↗

PubMed2003

Subcellular localization of ADPglucose pyrophosphorylase in developing wheat endosperm and analysis of the properties of a plastidial isoform.

The intracellular location of ADPglucose pyrophosphorylase (AGPase) in wheat during endosperm development was investigated by analysis of the recovery of marker enzymes from amyloplast preparations. Amyloplast preparations contained 20-28% of the total endosperm activity of two plastidial marker enzymes and less than 0.8% of the total endosperm activity of two cytosolic marker enzymes. Amylo plasts prepared at various stages of development, from 8-30 d post anthesis, contained between 2% and 10% of the total AGPase activity; this implies that between 7% and 40% of the AGPase in wheat endosperm is plastidial during this period of development. Two proteins were recognized by antibodies to both the large and small subunits of wheat AGPase. The larger of the two AGPases was the major form of the enzyme in whole cell extracts, and the smaller, less abundant, form of AGPase was enriched in plastid preparations. The results are consistent with data from other graminaceous endosperms, suggesting that there are distinct plastidial and cytosolic isoforms of AGPase composed of different subunits. The plastidial isoform of AGPase from wheat endosperm is relatively insensitive to the allosteric regulators 3-phosphoglycerate and inorganic orthophos phate compared with plastidial AGPase from other species. Amyloplast AGPase showed no sensitivity to physiological concentrations of inorganic orthophosphate. 15 mM 3-phosphoglycerate caused no stimulation of the pyrophosphorolytic reaction, and only 2-fold stimulation of the ADPglucose synthesizing reaction.

Cytosol↗

PubMed2002

The altered pattern of amylose accumulation in the endosperm of low-amylose barley cultivars is attributable to a single mutant allele of granule-bound starch synthase I with a deletion in the 5'-non-coding region.

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.

5' Flanking Region↗

PubMed2003

Metabolism of sugars in the endosperm of developing seeds of oilseed rape.

The sugars in the endosperm of a developing seed have many potential roles, including the supply of carbon to the developing embryo and controlling gene expression in it. Our understanding of their metabolism is, however, fragmentary and is confined to a very few species (especially Vicia spp.). To develop a quantitative understanding of the regulation of sugars in seeds of oilseed rape (Brassica napus), we measured relevant enzyme activities, the sizes of the pools of sugars in the liquid endosperm, and the flux of sugars from the endosperm into the embryo. The concentrations of hexose sugars in the liquid endosperm decreased, and sucrose (Suc) increased through development. The overall osmotic potential also fell. The timing of the changes was not precise enough to determine whether they signaled the onset of rapid accumulation of storage products. Changes in endosperm invertase activity were complex and quantitatively do not explain the changes in sugars. The embryo can metabolize hexose sugars in addition to Suc, and possibly at higher rates. Therefore, in addition to invertase, the growing embryo itself has a potential to influence the balance of sugars in the endosperm. The activity of Suc synthase in the embryo was greater than that of invertase during development. This observation and a higher activity of fructokinase than glucokinase in the embryo are both consistent with the embryo using Suc as a carbon source.

Brassica napus↗

PubMed2003

Comparative transcriptional profiling of placenta and endosperm in developing maize kernels in response to water deficit.

The early post-pollination phase of maize (Zea mays) development is particularly sensitive to water deficit stress. Using cDNA microarray, we studied transcriptional profiles of endosperm and placenta/pedicel tissues in developing maize kernels under water stress. At 9 d after pollination (DAP), placenta/pedicel and endosperm differed considerably in their transcriptional responses. In placenta/pedicel, 79 genes were significantly affected by stress and of these 89% were up-regulated, whereas in endosperm, 56 genes were significantly affected and 82% of these were down-regulated. Only nine of the stress-regulated genes were in common between these tissues. Hierarchical cluster analysis indicated that different sets of genes were regulated in the two tissues. After rewatering at 9 DAP, profiles at 12 DAP suggested that two regulons exist, one for genes responding specifically to concurrent imposition of stress, and another for genes remaining affected after transient stress. In placenta, genes encoding recognized stress tolerance proteins, including heat shock proteins, chaperonins, and major intrinsic proteins, were the largest class of genes regulated, all of which were up-regulated. In contrast, in endosperm, genes in the cell division and growth category represented a large class of down-regulated genes. Several cell wall-degrading enzymes were expressed at lower levels than in controls, suggesting that stress delayed normal advance to programmed cell death in the central endosperm. We suggest that the responsiveness of placenta to whole-plant stress factors (water potential, abscisic acid, and sugar flux) and of endosperm to indirect factors may play key roles in determining the threshold for kernel abortion.

Abscisic Acid↗