Microtubules in early development of the megagametophyte of <Emphasis Type="Italic">Ginkgo biloba</Emphasis>

Food storage tissue in the seeds of gymnosperms is female gametophyte (megagametophyte) that develops before fertilization, whereas, in seeds of angiosperms, food is stored as endosperm initiated by double fertilization. The megagametophyte is haploid, and endosperm is usually triploid, at least initially. Despite differences in origin, ploidy level, and developmental trigger, the early events of female gametophyte development in ginkgo are very similar to nuclear endosperm development in the seeds of angiosperms. In both, development begins as a single cell that undergoes multiple mitoses without cytokinesis, to produce a large syncytium. This study provided evidence that microtubule involvement in organization of the syncytium into nuclear cytoplasmic domains (NCDs) via nuclear-based radial microtubule systems is a critical developmental feature in the ginkgo megagametophyte, as it is in endosperm. Once the initial anticlinal walls have been deposited at the boundaries of NCDs, cellularization proceeds by the process of alveolation. Continued unidirectional growth of the alveolar walls is an outstanding example of polar cytokinesis. Ginkgo megagametophyte development appears to occur uniformly throughout the entire chamber, whereas nuclear type endosperm usually exhibits distinct developmental domains. These observations suggest that there is a fundamental pathway for the development and cellularization of syncytia in seed development.     

Abortive seed development in Ulmus minor (Ulmaceae)

Three genotypes of field elm ( Ulmus minor ) were studied to determine the structural basis of seed abortion in this species. In the non-abortive control, P-VV1, the pattern of seed development is similar to many flowering plants. The embryo progresses through defined morphological stages leading to developmental arrest as the seed matures. Storage products are abundant within embryo cells. Endosperm development is similar to the nuclear type; however, a more extensive cellularization of the endosperm occurs prior to it being crushed by the expanding embryo. For the abortive genotypes, M-SF1 and V-JR1, abnormalities in endosperm development are found. This is judged by the early cellularization and the massive synthesis of the PAS-positive material in the cellular endosperm. In these abortive genotypes, embryo development is delayed and storage products failed to accumulate within embryo cells. After seed desiccation, no living embryo tissue remains within the seed coat in the abortive genotypes.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 455–467.     

The evolution of embryogeny in seed plants and the developmental origin and early history of endosperm

For almost a century, the formation of endosperm from a second and distinctive fertilization event has been viewed as a unique feature of flowering plants. However, until recently, the evolutionary origin of this unique embryo-nourishing entity remained a mystery. Based upon comparative developmental analysis of reproduction among basal angiosperms and their closest extant relatives, the Gnetales (Ephedra, Gnetum, and Welwitschia), it is possible to construct an explicit hypothesis of the events that led to the evolutionary establishment of double fertilization and endosperm. The formulation of this historical record is derived entirely from and dependent upon the determination of reproductive features that are likely to have characterized the common ancestors of angiosperms and Gnetales. Current evidence is most congruent with the concept that a process of double fertilization first evolved in a common ancestor of the Gnetales and angiosperms. Initially, however, the second fertilization product was diploid and yielded a supernumerary embryo. Subsequent to the divergence of the angiosperm lineage from its closest relatives (which include the Gnetales), modification of the development of the supernumerary embryo (derived from the second fertilization event) led to the establishment of an embryo-nourishing endosperm. Comparative analysis of patterns of embryogeny within Gnetales and angiosperms establishes that embryo development in the ancestors of flowering plants (with a rudimentary process of double fertilization) was ab initio cellular, and not free nuclear, as had previously been assumed. Thus, it is likely that the earliest flowering plants displayed an ab initio cellular pattern of endosperm development, whose expression was inherited from that of the supernumerary embryo of the ancestors of flowering plants.     

Reproductive development and nuclear DNA content in angiosperms

Correlates of nuclear DNA content in angiosperms have been noted previously for a range of features, cellular to geographic. A new hypothesis, the correlation between nuclear DNA content and reproductive developmental features (after Cavalier-Smith, Journal of Cell Science 34, 247–268, 1978) is posed and tested here. Of three features tested (megasporogenesis, microsporogenesis, and endosperm development), megasporogenesis alone was shown to be correlated with nuclear DNA amount. The hypothesis was examined in 107 families of angiosperms using nonparametric statistics, and in 53 families of monocotyledons and outgroups using a phylogenetic test of association. A correlation was found between large genomes and successive microsporogenesis for all angiosperms, but not for monocots and dicots analyzed separately, thus underlining the importance of taking into account phylogenetic relationships in such studies. A correlation between cellular endosperm and large genomes in dicotyledons needs to be confirmed in a phylogenetic context. A tendency for deviations from monosporic megasporogenesis to occur in taxa that have a nuclear DNA content of over 9.0 pg/C was demonstrated using both phylogenetic and nonphylogenetic tests. It is hypothesized that cytoskeleton dynamics are affected in reproductive cells, enabling decoupling between nuclear and cytoplasmic cell cycles and leading to variation in reproductive development.     

The onset of embryo maturation in Arabidopsis is determined by its developmental stage and does not depend on endosperm cellularization

Seeds are dormant and desiccated structures, filled with storage products to be used after germination. These properties are determined by the maturation program, which starts, in Arabidopsis thaliana, mid‐embryogenesis, at about the same time and developmental stage in all the seeds in a fruit. The two factors, chronological and developmental time, are closely entangled during seed development, so their relative contribution to the transition to maturation is not well understood. It is also unclear whether that transition is determined autonomously by each seed or whether it depends on signals from the fruit. The onset of maturation follows the cellularization of the endosperm, and it has been proposed that there exists a causal relationship between both processes. We explored all these issues by analyzing markers for maturation in Arabidopsis mutant seeds that develop at a slower pace, or where endosperm cellularization happens too early, too late, or not at all. Our data show that the developmental stage of the embryo is the key determinant of the initiation of maturation, and that each seed makes that transition autonomously. We also found that, in contrast with previous models, endosperm cellularization is not required for the onset of maturation, suggesting that this transition is independent of the hexose/sucrose ratio in the seed. Our observations indicate that the mechanisms that control endosperm cellularization, embryo growth, and embryo maturation act independently of each other.     

The origin and maintenance of nuclear endosperms: viewing development through a phylogenetic lens

The endosperm develops in fertilized ovules of angiosperms following fertilization of the central cell and nuclei in the female gametophyte. Endosperms differ in whether, and which, nuclear divisions are followed by cellular divisions; the variants are classified as cellular, nuclear or helobial. Functional correlates of this variation are little understood. Phylogenetic methods provide a powerful means of exploring taxonomic variation and phylogenetic patterns, to frame questions regarding biological processes. Data on endosperms across angiosperms were analysed in a phylogenetic context in order to determine homologies and detect biases in the direction of evolutionary transitions. Analyses confirm that neither all nuclear nor all helobial endosperms are homologous, raise the possibility that cellular development is a reversal in some derived angiosperms (e.g. asterids) and show that a statistically significant bias towards evolution of nuclear endosperms (and against reversals) prevails in angiosperms as a whole. This bias suggests strong selective advantages to having nuclear endosperm, developmental constraints to reversals or both. Homologies suggest that the microtubular cycle and cellularization pattern characteristic of reproductive cells across land plants may have been independently co-opted during multiple origins of nuclear endosperms, but information on cellular endosperms is essential to investigate further.     

Endosperm cellularization defines an important developmental transition for embryo development

The endosperm is a terminal seed tissue that is destined to support embryo development. In most angiosperms, the endosperm develops initially as a syncytium to facilitate rapid seed growth. The transition from the syncytial to the cellularized state occurs at a defined time point during seed development. Manipulating the timing of endosperm cellularization through interploidy crosses negatively impacts on embryo growth, suggesting that endosperm cellularization is a critical step during seed development. In this study, we show that failure of endosperm cellularization in fertilization independent seed 2 (fis2) and endosperm defective 1 (ede1) Arabidopsis mutants correlates with impaired embryo development. Restoration of endosperm cellularization in fis2 seeds by reducing expression of the MADS-box gene AGAMOUS-LIKE 62 (AGL62) promotes embryo development, strongly supporting an essential role of endosperm cellularization for viable seed formation. Endosperm cellularization failure in fis2 seeds correlates with increased hexose levels, suggesting that arrest of embryo development is a consequence of failed nutrient translocation to the developing embryo. Finally, we demonstrate that AGL62 is a direct target gene of FIS Polycomb group repressive complex 2 (PRC2), establishing the molecular basis for FIS PRC2-mediated endosperm cellularization.     

Rice caryopsis development Ⅱ: Dynamic changes in the endosperm

The rice endosperm plays crucial roles in nourishing the embryo during embryogenesis and seed germination. Although previous studies have provided the general information about rice endosperm, a systematic investigation throughout the entire endosperm developmental process is still lacking. In this study, we examined in detail rice endosperm development on a daily basis throughout the 30‐day period of post‐fertilization development. We observed that coenocytic nuclear division occurred in the first 2 days after pollination (DAP), cellularization occurred between 3 and 5 DAP, differentiation of the aleurone and starchy endosperm occurred between 6 and 9 DAP, and accumulation of storage products occurred concurrently with the aleurone/starchy endosperm differentiation from 6 DAP onwards and was accomplished by 21 DAP. Changes in cytoplasmic membrane permeability, possibly caused by programmed cell death, were observed in the central region of the starchy endosperm at 8 DAP, and expanded to the whole starchy endosperm at 21 DAP when the aleurone is the only living component in the endosperm. Further, we observed that a distinct multi‐layered dorsal aleurone formed near the dorsal vascular bundle, while the single‐ or occasionally two‐cell layered aleurone was located in the lateral and ventral positions of endosperm. Our results provide in detail the dynamic changes in mitotic divisions, cellularization, cell differentiation, storage product accumulation, and programmed cell death that occur during rice endosperm development.     

Embryological problems in the apomictic speciesChondrilla juncea L. (Compositae)

Examination of the embryo and endosperm development in triploidChondrilla juncea L. (2n=15) from Poland confirmed the occurrence of autonomous apomixis in this species. Numerous degenerated embryos were formed which might be one of the factors which increased the observed seed sterility. In addition, twin embryos were often found at young developmental stages and in germinating seeds. Endosperm developed from polar nuclei or from the secondary nucleus. These processes have been proved by counting chromosome numbers in early developmental stages of the endosperm. The problems of the prevailing type of endosperm (nuclear or cellular), the correlation of embryo and endosperm development and the period of cellularization of nuclear endosperm have remained unsolved.     

Perspective: the origin of flowering plants and their reproductive biology--a tale of two phylogenies

Recently, two areas of plant phylogeny have developed in ways that could not have been anticipated, even a few years ago. Among extant seed plants, new phylogenetic hypotheses suggest that Gnetales, a group of nonflowering seed plants widely hypothesized to be the closest extant relatives of angiosperms, may be less closely related to angiosperms than was believed. In addition, recent phylogenetic analyses of angiosperms have, for the first time, clearly identified the earliest lineages of flowering plants: Amborella, Nymphaeales, and a clade that includes Illiciales/ Trimeniaceae/Austrobaileyaceae. Together, the new seed plant and angiosperm phylogenetic hypotheses have major implications for interpretation of homology and character evolution associated with the origin and early history of flowering plants. As an example of the complex and often unpredictable interplay of phylogenetic and comparative biology, we analyze the evolution of double fertilization, a process that forms a diploid embryo and a triploid endosperm, the embryo-nourishing tissue unique to flowering plants. We demonstrate how the new phylogenetic hypotheses for seed plants and angiosperms can significantly alter previous interpretations of evolutionary homology and firmly entrenched assumptions about what is synapomorphic of flowering plants. In the case of endosperm, a solution to the century-old question of its potential homology with an embryo or a female gametophyte (the haploid egg-producing generation within the life cycle of a seed plant) remains complex and elusive. Too little is known of the comparative reproductive biology of extant nonflowering seed plants (Gnetales, conifers, cycads, and Ginkgo) to analyze definitively the potential homology of endosperm with antecedent structures. Remarkably, the new angiosperm phylogenies reveal that a second fertilization event to yield a biparental endosperm, long assumed to be an important synapomorphy of flowering plants, cannot be conclusively resolved as ancestral for flowering plants. Although substantive progress has been made in the analysis of phylogenetic relationships of seed plants and angiosperms, these efforts have not been matched by comparable levels of activity in comparative biology. The consequence of inadequate comparative biological information in an age of phylogenetic biology is a severe limitation on the potential to reconstruct key evolutionary historical events.     

Developmental and evolutionary hypotheses for the origin of double fertilization and endosperm.

The discovery of a second fertilization event that initiates endosperm in flowering plants, just over a century ago, stimulated intense interest in the evolutionary history and homology of endosperm, the genetically biparental embryo-nourishing tissue that is found only in angiosperms. Two alternative hypotheses for the origin of double fertilization and endosperm have been invoked to explain the origin of the angiosperm reproductive syndrome from a typical non-flowering seed plant reproductive syndrome. Endosperm may have arisen from a developmental transformation of a supernumerary embryo derived from a rudimentary second fertilization event that first evolved in the ancestors of angiosperms (endosperm homologous with an embryo). Conversely, endosperm may represent the developmental transformation of the cellular phase of non-flowering seed plant female gametophyte ontogeny that was later sexualized by the addition of a second fertilization event in a strongly progenetic female gametophyte (endosperm homologous with a female gametophyte). For the first time, explicit developmental and evolutionary transitions for both of these hypotheses are examined and compared. In addition, current data that may be congruent with either of these hypotheses are discussed. It is clear that much remains to be accomplished if the evolutionary significance of the process of double fertilization and the formation of endosperm is to be fully understood.     

水稻淀粉胚乳程序性细胞死亡中的去核化

对水稻品种中籼8836淀粉胚乳细胞的去核化发育阶段的细胞超微结构变化和同期籽粒灌浆速率及相关酶活性的动态进行了观察和分析。开花受精后约在第3天胚乳完成细胞化,花后第5天少数淀粉胚乳细胞启动去核发育过程。核消亡是淀粉胚乳细胞程序性细胞死亡(PCD)的第一步。同一籽粒淀粉胚乳细胞的去核进程是不同步的。花后第13天所有淀粉胚乳细胞都已完成去核过程。在去核过程中,胚乳核的形态变化特征既有动植物PCD的共性又有其特殊性。伴随核降解过程,一部分线粒体解体,表明去核化与线粒体解体有一定联系。在去核化发育阶段,与PCD有关的酶类,如超氧化物歧化酶(SOD)过氧化氢酶(CAT)活性非常高;与淀粉合成有关的酶类,如ADPG焦磷酸化酶、可溶性淀粉合成酶(SSS酶)、淀粉分支酶(或Q酶)也表现出很高的活性。去核化发育阶段籽粒灌浆速率最高,籽粒增重亦最快。淀粉胚乳细胞去核之后,细胞并未立即死亡,这些无核的细胞仍维持正常有序的代谢活动,继续进行淀粉和贮藏蛋白的合成与积累,但上述酶类的活性明显降低,灌浆速率也明显趋缓。淀粉胚乳细胞最终被贮藏物质充满时成为死细胞,完成其程序性死亡过程。Evan’s blue染色鉴定表明淀粉胚乳细胞死亡不同步,细胞死亡在淀粉胚乳组织中是随机发生的。     

白刺胚乳早期发育的超微结构研究

白刺(Nitraria sibirica)胚乳发育经历游离核阶段、细胞化阶段和被吸收解体阶段。游离核胚乳沿胚囊壁均匀排列为一层,胞质浓厚,其中有丰富的质体、线粒体、高尔基体、内质网和各种小泡等细胞器。珠孔区域的胚囊壁具发达的分枝状壁内突,而周缘区域的胚囊壁具间隔的钉状内突,内突周围的细胞质中具多数线粒体和小泡。胚乳细胞化时,初始垂周壁源于核有丝分裂产生的细胞板。在细胞板两端开始壁的游离生长,一端与胚囊壁相连接,另一端向心自由延伸。壁的游离生长依赖于小泡的融合。早期胚乳细胞具大液泡,具核或无核,细胞质中有大量的线粒体,质体缺乏,其壁仍由多层膜结构组成。     

The cytoskeleton and spatial control of cytokinesis in the plant life cycle

Summary One of the intriguing aspects of development in plants is the precise control of division plane and subsequent placement of walls resulting in the specific architecture of tissues and organs. The placement of walls can be directed by either of two microtubule cycles. The better known microtubule cycle is associated with control of the future division plane in meristematic growth where new cells become part of tissues. The future daughter domains are determined before the nucleus enters prophase and the future site of cytokinesis is marked by a preprophase band (PPB) of cortical microtubules. The spindle axis is then organized in accordance with the PPB and, following chromosome movement, a phragmoplast is initiated in the interzone and expands to join with parental walls at the site previously occupied by the PPB. The alternative microtubule cycle lacks both the hooplike cortical microtubules of interphase and the PPB. Wall placement is determined by a radial microtubule system that defines a domain of cytoplasm either containing a nucleus or destined to contain a nucleus (the nuclear cytoplasmic domain) and controls wall placement at its perimeter. This more flexible system allows for cytoplasmic polarization and migration of nuclei in coenocytes prior to cellularization. The uncoupling of cytokinesis from karyokinesis is a regular feature of the reproductive phase in plants and results in specific, often unusual, patterns of cells which reflect the position of nuclei at the time of cellularization (e.g., the arrangement of spores in a tetrad, cells of the male and female gametophytes of angiosperms, and the distinctive cellularization of endosperm). Thus, both microtubule cycles are required for completion of plant life cycles from bryophytes to angiosperms. In angiosperm seed development, the two methods of determining the boundaries of domains where walls will be deposited are operative side by side. Whereas the PPB cycle drives embryo development, the radial-microtubule-system cycle drives the common nuclear type of endosperm development from the syncytial stage through cellularization. However, a switch to the PPB cycle can occur in endosperm, as it does in barley, when peripheral cells divide to produce a multilayered aleurone. The triggers for the switch between microtubule cycles, which are currently unknown, are key to understanding plant development.Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday     

HETEROCHRONY AND DEVELOPMENTAL INNOVATION: EVOLUTION OF FEMALE GAMETOPHYTE ONTOGENY IN GNETUM,A HIGHLY APOMORPHIC SEED PLANT

Seed plant female gametophytes are focal points for the evolutionary modification of development. From a structural perspective, the most divergent female gametophytes among all seed plants are found in Gnetum, a clade within Gnetales. Coenocytic organization at sexual maturity, absence of defined egg cells (free nuclei are fertilized), lack of centripetal cellularization, and postfertilization development of embryo-nourishing tissues are features of the female gametophytes of Gnetum unparalleled among seed plants. Although the female gametophyte of Gnetum retains the three basic phases of somatic development common to female gametophytes of plesiomorphic seed plants (free nuclear development, cellularization, cellular growth), the timing of fertilization has been accelerated relative to the rate of somatic development. As a consequence, the female gametophyte of Gnetum matures sexually (is fertilized) at a juvenile (compared with the ancestral somatic ontogeny) and free nuclear stage of somatic development, thereby precluding differentiation of egg cells. Unlike progenetic animals, where truncation of somatic ontogeny evolves in tandem with acceleration in the timing of sexual maturation, the female gametophyte of Gnetum completes the entire ancestral somatic ontogeny after precocious sexual maturation. This results in the evolution of postfertilization development of embryo-nourishing female gametophyte tissues, a phenomenon unique among seed plants. Nonheterochronic developmental innovations have also played important roles in the evolution of the female gametophyte of Gnetum. Centripetal cellularization, which is always associated with the phase change from coenocytic to cellular organization among plesiomorphic seed plant female gametophytes, is lacking in Gnetum. Instead, during early phases of development, apomorphic free nuclear organization is coupled with a highly anomalous pattern of cellularization. Stage-specific innovations during early development in the female gametophyte of Gnetum do not affect plesiomorphic aspects of later phases of development. Thus, a complex array of heterochronic and nonheterochronic developmental innovations have played critical roles in the ontogenetic evolution of the highly apomorphic female gametophyte of Gnetum.     

The endosperm development and the variations of structures of embryo sacs: unravelling the low fecundity of Zephyranthes candida (Amaryllidaceae)

To unravel a low fecundity in Zephyranthes candida (Lindl.) Herb., the development of the endosperm was studied using conventional paraplast section technique. The results show that the endosperm develops normally and comprises four major stages viz. syncytial, cellularization, differentiation and maturation. Both proliferation of antipodal cells and their close contact with the primary endosperm nucleus were observed, which should favor transportation of nutrients and accelerate development of embryo and endosperm. In Z. candida, at least four events of nuclear migration occurred during the course of embryogenesis and endosperm development. The 12.7% structurally and functionally abnormal ovules, along with the 22.3% collapsed and aborted ovules observed accounts for the low fecundity to some extent.     

柽柳胚和胚乳发育的观察

利用常规石蜡制片技术,对柽柳（Tamarix chinensis Lour.）胚和胚乳的发育过程进行了观察。结果表明,胚发育属茄型,其基细胞先行纵裂。胚柄基部发育迅速,具吸器作用,球形胚期胚柄最为发达,其细胞质丰富,贮藏淀粉类物质,至晚心形胚期胚柄依然存在。助细胞被受精产生多胚现象。胚乳发育属核型,初生胚乳核常常晚于合子分裂,胚乳核的分裂速度慢于胚体细胞的分裂速度。当胚乳游离核为 32个时,以自由生长细胞壁的方式进行胚乳细胞化。胚乳细胞进一步增殖极少。珠心细胞只有两层,细胞核大,胞质丰富,内含贮藏物质,至心形胚期逐渐解体。     

Ultrastructural study of change from free-nuclear to cellular endosperm in Ipomoea purpurea Roth and Cytinus hypocistis L.

Abstract

The process of cellularization of the endosperm was studied in Ipomoea purpurea Roth and Cytinus hypocistis L. In both the examined species normal cytochinesis, involving the formation of the phragmoplast, characterizes the change from the nuclear to cellular condition. Nevertheless, some ultrastructural aspects of the cell wall initiation seem to indicate that the modality of freely-growing walls cannot be excluded. The hypothesis of a unique method of wall initiation for the endosperm of the nuclear type, formulated by some Authors, is discussed.     

Mutants in the imprinted PICKLE RELATED 2 gene suppress seed abortion of fertilization independent seed class mutants and paternal excess interploidy crosses in Arabidopsis

Endosperm cellularization is essential for embryo development and viable seed formation. Loss of function of the FERTILIZATION INDEPENDENT SEED (FIS) class Polycomb genes, which mediate trimethylation of histone H3 lysine27 (H3K27me3), as well as imbalanced contributions of parental genomes interrupt this process. The causes of the failure of cellularization are poorly understood. In this study we identified PICKLE RELATED 2 (PKR2) mutations which suppress seed abortion in fis1/mea by restoring endosperm cellularization. PKR2, a paternally expressed imprinted gene (PEG), encodes a CHD3 chromatin remodeler. PKR2 is specifically expressed in syncytial endosperm and its maternal copy is repressed by FIS1. Seed abortion in a paternal genome excess interploidy cross was also partly suppressed by pkr2. Simultaneous mutations in PKR2 and another PEG, ADMETOS (ADM), additively rescue the seed abortion in fis1 and in the interploidy cross, suggesting that PKR2 and ADM modulate endosperm cellularization independently and reproductive isolation between plants of different ploidy is established by imprinted genes. Genes upregulated in fis1 and downregulated in the presence of pkr2 are enriched in glycosyl‐hydrolyzing activity, while genes downregulated in fis1 and upregulated in the presence of pkr2 are enriched with microtubule motor activity, consistent with the cellularization patterns in fis1 and the suppressor line. The antagonistic functions of FIS1 and PKR2 in modulating endosperm development are similar to those of PICKLE (PKL) and CURLY LEAF (CLF), which antagonistically regulate root meristem activity. Our results provide further insights into the function of imprinted genes in endosperm development and reproductive isolation.     

Rice interspecies hybrids show precocious or delayed developmental transitions in the endosperm without change to the rate of syncytial nuclear division

In angiosperms, interspecific crosses often display hybrid incompatibilities that are manifested as under‐proliferation or over‐proliferation of endosperm. Recent analyses using crosses between Arabidopsis thaliana and its related species with different ploidy levels have shown that interspecific hybridization causes delayed developmental transition and increased mitotic activity in the endosperm. In this study, we investigated endosperm development in interspecific crosses between diploid Oryza species. In a cross between female O. sativa and male O. punctata, we found that the hybrid endosperm was reduced in size and this cross was associated with precocious developmental transition. By contrast, the cross between O. sativa and O. longistaminata generated enlarged hybrid endosperm at the mid‐point of seed development and this cross was associated with delayed developmental transition. Subsequently, the hybrid endosperm displayed a shriveled appearance at the seed maturation stage. We found that the accumulation of storage products and the expression patterns of several marker genes were also altered in the hybrid endosperm. By contrast, the rate of syncytial mitotic nuclear divisions was not significantly affected. The gene OsMADS87 showed a maternal origin‐specific expression pattern in rice endosperm, in contrast to its Arabidopsis homologue PHERES1, which shows paternal origin‐specific expression. OsMADS87 expression was decreased or increased depending on the type of developmental transition change in the hybrid rice endosperm. Our results indicate that one of the interspecies hybridization barriers in Oryza endosperm is mediated by precocious or delayed developmental alterations and de‐regulation of OsMADS87, without change to the rate of syncytial mitotic nuclear division in the hybrid endosperm.