Dual-Carbon Batteries: Materials and Mechanism.

Various carbon nanomaterials are being widely studied for applications in supercapacitors and Li-ion batteries as well as hybrid energy storage devices. Dual-carbon batteries (DCBs), in which both electrodes are composed of functionalized carbon materials, are capable of delivering high energy/power and stable cycles when they are rationally designed. This Review focuses on the electrochemical reaction mechanisms and energy storage properties of various carbon electrode materials in DCBs, including graphite, graphene, hard and soft carbon, activated carbon, and their derivatives. The interfacial chemistry between carbon electrodes and electrolyte is also discussed. The perspective for further development of DCBs is presented at the end.

Synthesis of the Carbon-Coated Nanoparticle Co9S8 and Its Electrochemical Performance as an Anode Material for Sodium-Ion Batteries.

A Co9S8/C nanocomposite is prepared using a solid-state reaction followed by a facile mechanical ball-milling treatment, with sucrose as the carbon source. The phases, morphologies, and detailed structures of the Co9S8/C nanocomposite are well-characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. When evaluated as an anode material for sodium-ion batteries, the Co9S8/C nanocomposite electrode displays a reversible capacity of ∼567 mA h g-1 in the initial cycle and maintains a reversible capacity of ∼320 mA h g-1 after 30 cycles, indicating a larger capacity and a stable cycling performance. For comparison, the electrochemical performances of Co9S8 and Co9S8/C samples synthesized using the solid-state reaction are also displayed. The ex situ XRD and transmission electron microscopy tests demonstrate that Co9S8 undergoes a conversion-type sodium storage mechanism.

Superstructure ZrV2O7 nanofibres: thermal expansion, electronic and lithium storage properties.

ZrV2O7 has attracted much attention as a negative thermal expansion (NTE) material due to its isotropic negative structure. However, rarely has investigation of the lithium storage behaviors been carried out except our first report on it. Meanwhile, the electrochemical behaviors and energy storage characteristics have not been studied in depth and will be explored in this article. Herein, we report on the synthesis, characterization and lithium intercalation mechanism of superstructure ZrV2O7 nanofibres that were prepared through a facile solution-based method with a subsequent annealing process. The thermal in situ XRD technique combined with the Rietveld refinement method is adopted to analyze the change in the temperature-dependent crystal structure. Benefiting from the nanostructured morphology and relatively high electronic conductivity, it presents acceptable cyclic stability and rate capability. According to the operando evolution of the XRD patterns obtained from electrochemical in situ measurements, the Li intercalation mechanism of the solid solution process with a subsequent conversion reaction can be concluded. Finally, the amorphous state of the electrodes after the initial fully discharged state can effectively enhance the electrochemical performances.

OsFIE2 plays an essential role in the regulation of rice vegetative and reproductive development.

Polycomb group (PcG) proteins are gene repressors that help to maintain cellular identity during development via chromatin remodeling. Fertilization-independent endosperm (FIE), a member of the PcG complex, operates extensively in plant development, but its role in rice has not been fully investigated to date. We report the isolation and characterization of a PcG member in rice, which was designated OsFIE2 for Oryza sativa Fertilization-Independent Endosperm 2. OsFIE2 is a single-copy gene in the rice genome and shows a universal expression pattern. The OsFIE2 RNAi lines displayed pleiotropic phenotypes in vegetative and reproductive organ generation. In unfertilized lines, endosperm formation could be triggered without embryo formation, which indicates that FIE is indeed involved in the suppression of autonomous endosperm development in rice. Furthermore, lateral root generation was promoted early in the roots of OsFIE2 RNAi lines, whereas the primary root was premature and highly differentiated. As the root tip stem cell differentiated, QHB, the gene required for stem cell maintenance in the quiescent center, was down-regulated. Our data suggest that the OsFIE2-PcG complex is vital for rice reproduction and endosperm formation. Its role in stem cell maintenance suggests that the gene is functionally conserved in plants as well as animals.

The garden asparagus (Asparagus officinalis L.) mitochondrial genome revealed rich sequence variation throughout whole sequencing data.

Garden asparagus (Asparagus officinalis L.) is a horticultural crop with high nutritional and medical value, considered an ideal plant for sex determination research among many dioecious plants, whose genomic information can support genetic analysis and breeding programs. In this research, the entire mitochondrial genome of A. officinalis was sequenced, annotated and assembled using a mixed Illumina and PacBio data. The garden asparagus circular mitochondrial genome measures 492,062 bp with a GC value of 45.9%. Thirty-six protein-coding genes, 17 tRNA and 6 rRNA genes were annotated, among which 8 protein-coding genes contained 16 introns. In addition, 254 SSRs with 10 complete tandem repeats and 293 non-tandem repeats were identified. It was found that the codons of edited sites located in the amino acids showed a leucine-formation trend, and RNA editing sites mainly caused the mutual transformation of amino acids with the same properties. Furthermore, 72 sequence fragments accounting for 20,240 bp, presentating 4.11% of the whole mitochondrial genome, were observed to migrate from chloroplast to mitochondrial genome of A. officinalis. The phylogenetic analysis showed that the closest genetic relationship between A. officinalis with onion (Allium cepa) inside the Liliaceae family. Our results demonstrated that high percentage of protein-coding genes had evolutionary conservative properties, with Ka/Ks values less than 1. Therefore, this study provides a high-quality garden asparagus mitochondrial genome, useful to promote better understanding of gene exchange between organelle genomes.

Integrating molybdenum into zinc vanadate enables Zn3V2MoO8 as a high-capacity Zn-supplied cathode for Zn-metal free aqueous batteries.

The commercialization of aqueous zinc-ion batteries (AZIBs) has been hindered by the obsession with Zn-metal anode, just like the early days of lithium-ion batteries. Developing Zn-metal free aqueous batteries (ZFABs) with superior Zn-supplied cathodes is a promising way to escape this predicament. Herein, a novel mixed transition-metal spinel, Zn3V2MoO8, has been synthesized via a sol-gel technique and proposed as a Zn-supplied cathode material. Utilizing the synergistic effect of vanadium and molybdenum, Zn3V2MoO8 can provide a high capacity of 360.3 mA h g-1 at 100 mA g-1, which is the state-of-the-art in existing Zn-supplied cathodes, and the capacity retention is 82% over 700-4500 cycles at 10 A g-1. The mechanism is that Zn3V2MoO8 undergoes a phase transition to Zny(V,Mo)2O5-x·nH2O in the initial charge, and then protons and zinc ions intercalate/deintercalate concurrently into/from the new host. To construct ZFABs with a Zn3V2MoO8 cathode, two non-zinc materials (brass and 9,10-anthraquinone) are used as anodes. Thereby, the Zn3V2MoO8||9,10AQ battery reveals a more satisfactory electrochemical performance, with a stable capacity of 100.4 mA h g-1 lasting for 200 cycles, which provides a feasible scheme for the practical application of AZIBs.

The entire chloroplast genome sequence of Asparagus setaceus (Kunth) Jessop: Genome structure, gene composition, and phylogenetic analysis in Asparagaceae.

Asparagus setaceus (Kunth) Jessop is a horticultural plant of the genus Asparagus. Herein, the whole chloroplast (cp) genome of A. setaceus was sequenced with PacBio and Illumina sequencing systems. The cp genome shows a characteristic quadripartite structure with 158,076 bp. In total, 135 genes were annotated, containing 89 protein-coding, 38 tRNA, and 8 rRNA genes. Contrast with the previous cp genome of A. setaceus registered in NCBI, we identified 7 single-nucleotide polymorphisms and 15 indels, mostly situated in noncoding areas. Meanwhile, 36 repeat structures and 260 simple sequence repeats were marked out. A bias for A/T-ending codons was shown in this cp genome. Furthermore, we predicted 78 RNA-editing sites in 29 genes, which were all for C-to-U transitions. And it was also proven that positive selection was exerted on the rpoC1 gene of A. setaceus with the K a/K s data. Meanwhile, a conservative gene order and highly similar sequences of protein-coding genes were revealed within Asparagus species. Phylogenetic tree analysis indicated that A. setaceus was a sister to Asparagus cochinchinensis. Taken together, our released genome provided valuable information for the gene composition, genetics comparison, and the phylogeny studies of A. setaceus.

A novel strategy via electrode catalysis induced nano transformation for lithiated-bimetallic-oxides to avoid the long activation process of advanced lithium-ion batteries.

Improving the anode materials for lithium-ion batteries with a long activation process, poor cycle stability, and low Coulomb efficiency is of great significance for developing novel high-performance anode materials. Orthorhombic LiVMoO5 with high specific capacity was applied to the anode field of lithium-ion battery for the first time. However, the activation process led to its poor cyclic performance. By adopting a novel nano-transformation treatment process in a water and oxygen environment, we effectively avoided the long-term activation process. The specially treated LiVMoO5 electrode (STLVME) exhibited excellent reversible specific capacity (∼1100 mA h g-1) and rate cycle stability (capacity retention rate ∼100%). Furthermore, GITT and EIS also showed that compared with the primitive LiVMoO5 electrode (LVME), smaller internal resistance and a higher Li+ diffusion coefficient were caused using the novel treatment process, significantly improving the rate cycle stability. Using in situ XRD and ex situ characterization, we illustrated the lithium storage mechanism of LVME and STLVME. In addition, the practical application potential of LVME and STLVME was also explored by assembling the full cells. Because the long-term activation process was effectively avoided, the full-cell exhibited amazing cycle stability, indicating that STLVME can be considered a promising potential anode for practical applications in energy storage devices.

Insights into the enhanced electrochemical performance of MnV2O6 nanoflakes as an anode material for advanced lithium storage.

Binary transition metal oxides (BTMOs) are regarded as potential anode materials for lithium-ion batteries (LIBs) owing to their low cost, high specific capacities, and environmental friendliness. In this work, MnV2O6 nanoflakes are successfully synthesized by a facile hydrothermal method. When evaluated as an anode material for LIBs, benefiting from the activation process, the as-prepared MnV2O6 nanoflake electrode delivers a high reversible specific capacity of 1439 mA h g-1 after 300 cycles at a current density of 200 mA g-1, and especially presents a specific capacity of 1010 mA h g-1 after 700 cycles at a higher current density of 1 A g-1. Furthermore, MnV2O6 shows a pleasurable rate capability; a reversible specific capacity of 867 mA h g-1 can be obtained at a current density of 2000 mA g-1, and when the current density is returned to 200 mA g-1 and continues for another 80 cycles, the specific capacity can still reach 1499 mA h g-1. Meanwhile, the morphology variation and electrochemical kinetic behavior of the MnV2O6 electrode during cycling are scrutinized in detail. After that, the electrochemical reaction mechanism of MnV2O6 during the discharge/charge process is corroborated by in situ X-ray diffraction (XRD), which involves the coexistence of a conversion reaction and solid solution behavior. The practical application of MnV2O6 nanoflakes as an anode material is examined as well. Sure enough, the NCM811//MnV2O6 full-cell exhibits excellent lithium-storage performance.

Cubic MnV2O4 fabricated through a facile sol-gel process as an anode material for lithium-ion batteries: morphology and performance evolution.

Metal vanadates have been popularly advocated as promising anode materials for lithium-ion batteries (LIBs) benefiting from their high theoretical specific capacity and abundant resources. Given that manganese and vanadium are reasonably economical elements and enjoy assorted redox reactions, they have extensive application prospects in energy storage systems. Here, we synthesized cubic MnV2O4 as an anode for LIBs by an efficient sol-gel process. As a result, the MnV2O4 electrode delivers distinguished electrochemical performance, including an appealing reversible specific capacity of nearly 1325 mA h g-1 for 500 cycles at 200 mA g-1, excellent cycling stability with a capacity of 399 mA h g-1 up to 500 cycles at 2000 mA g-1 and a favorable rate capability of 516/410 mA h g-1 at 1000/2000 mA g-1 (when the current density recuperates to 200 mA g-1, the specific capacity still boosts as the number of cycles increases). What's more, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) under various scan rates and scanning electron microscopy (SEM) are executed to ascertain with a greater depth the electrochemical kinetic characteristics and morphology of the MnV2O4 electrode in different states. These results make known that MnV2O4 is a credible anode material for LIBs, and such a facile and economical synthetic route can be extended to the preparation of other metal vanadate materials.

Unusual Dual-Site Substitution Adjusts the Degree of Stacking Disorder in Honeycomb Na3Ni2SbO6 Cathode for Sodium-Ion Batteries.

O'3-Na3Ni2SbO6 with a honeycomb cation order, as a potential cathode, presents simplified phase-transition steps and a high average voltage. To mitigate the intrinsic phase irreversibility, Mg, Zn, and Co have been introduced to displace part of the Ni, which inevitably reduces the theoretical capacity related to the Ni2+/Ni3+ redox reaction. In this work, an unusual dual-site substitution is carried out to increase the P'3-O'3 structure reversibility without sacrificing the practical capacity. In addition, it is found that special stacking faults along the c-axis direction can be induced by doping to result in incomplete Sb/Ni disorder, though the honeycomb order remains in every TM (transition-metal) layer. The codoped Na2.85Cs0.15Ni1.9Mg0.1SbO6 has a high degree of disorder, which breaks the ideal monoclinic symmetry (C2/m) and partly upgrades its structure to higher-symmetry models. Profiting from the influence of stacking disorder and doping ions on the coordination environment around Na, more gradual and smaller variations of the lattice parameters appear upon Na-ion extraction/insertion. Consequently, this cathode displays a high initial discharge capacity (120 mAh g-1), long-term cycling stability, and excellent rate performance (66 mAh g-1 under 10 C). These findings reveal that not only a full TM-disordered arrangement but also this incomplete stacking disorder can effectively improve the performance of a layered cathode.

Preparation and electrochemical performance of nanowire-shaped Na3Mn2-xFex(P2O7)(PO4) for sodium-ion and lithium-ion batteries.

A series of Fe-doped Na3Mn2-xFex(P2O7)(PO4) (x = 0, 0.2, 0.4) (abbreviated as NMFP-0/NMFP-0.2/NMFP-0.4) compounds have been successfully prepared using the sol-gel method. The Rietveld refinement results indicate that single-phase Na3Mn2-xFex(P2O7)(PO4) with an orthorhombic structure can be obtained. Our results reveal that by controlling the raw materials, the molar ratio of the reactants, the stirring rate of the precursor, the annealing temperature rate, and the reaction time, the proportion of nanowires in the morphology increases as the Fe component rises, and the NMFP-0.4 nanowire-shaped compounds show the best electrochemical activity when used as a cathode material for SIBs. Additionally, its specific capacity is enhanced to ∼126 mA h g-1 in the first cycle when operated at 0.1 C and a working potential window of 1.8-4.3 V (vs. Na/Na+). The material can also be applied in lithium-ion batteries as an anode and achieves ∼600 mA h g-1 specific capacity at a current density of 0.1 C (1 C = 1000 mA g-1) in a working potential window of 0.01-3 V (vs. Li/Li+).

Facile synthesis of one-dimensional vanadyl acetate nanobelts toward a novel anode for lithium storage.

Transition metal oxides (TMOs) are prospective anode materials for lithium-ion batteries (LIBs), owing to their high theoretical specific capacity. However, the inherently low conductivity of TMOs restricts their application. The coupling of lithium-ion conducting polymer ligands with TMO structures is favorable for the dynamics of electrochemical processes. Herein, vanadyl acetate (VA) nanobelts, an organic-inorganic hybrid material, are synthesized for the first time as an anode material for LIBs. As a result, the VA nanobelt electrode displays an outstanding electrochemical performance, including a highly stable reversible specific capacity (around 1065 mA h g-1 at 200 mA g-1), superior long-term cyclability (with a capacity of approximately 477 mA h g-1 at 2 A g-1 over 500 cycles) and attractive rate capability (1012 mA h g-1 when the current density recovers to 200 mA g-1). In addition, scanning electron microscopy (SEM), cyclic voltammetry (CV) curves at different scanning rates and electrochemical impedance spectroscopy (EIS) are used to investigate the variation of the specific capacity and the electrochemical kinetic characteristics of the VA electrode during cycling in detail, respectively. Also, the structural variations of the VA electrode in the initial two cycles are also investigated by in situ XRD testing. The periodic evolution of the in situ XRD patterns demonstrates that the VA nanobelt electrode shows excellent reversibility for Li+ ion insertion/extraction. This work offers an enlightening insight into the future research into organo-vanadyl hybrids as advanced anode materials.

The facile synthesis and electrochemical performance of Ni2V2O7 as a novel anode material for lithium-ion batteries.

The single-phase binary nickel vanadate Ni2V2O7 was successfully synthesized by a simple solid-state method to explore novel anode materials for lithium-ion batteries. After an activation process, the Ni2V2O7 electrode exhibited excellent electrochemical performance with a stable, high specific capacity of about 960 mA h g-1 at a current density of 100 mA g-1, which is attributed to the multiple valence states and the synergistic effect of the transition elements V and Ni. Even at a high current density of 2000 mA g-1, a stable specific capacity of about 400 mA h g-1 was still obtained. Considering the influence of the activation process on the electrochemical performance of the Ni2V2O7 electrode, we studied the origin of the excellent electrochemical performance, where the improved lithium diffusion coefficient and increased pseudocapacitive contribution caused by the activation process led to a significant improvement in the electrochemical performance, including rate capacity and cycle stability. By combining in situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) methods, for the first time, we illustrate the detailed lithium storage mechanism of the Ni2V2O7 electrode during the lithium insertion/extraction process.

In situ hydrothermal synthesis of double-carbon enhanced novel cobalt germanium hydroxide composites as promising anode material for sodium ion batteries.

Germanium (Ge)-based materials are considered to be one of the most promising anode materials for sodium-ion batteries (SIBs). Nevertheless, the practical electrochemical performance is severely hampered by poor cyclability due to volumetric expansion of Ge upon cycling. Herein, double-carbon confined cobalt germanium hydroxide (CGH@C/rGO) composites has been facilely synthesized with the supportion of l-ascorbic acid and graphene oxide (GO) as anode materials for sodium-ion storage. As a result, the CGH@C/rGO anode delivers a high cyclic stability with a reversible capacity of 416 mA h g-1 after 100 cycles at 100 mA g-1 and an excellent rate capability of 206 mA h g-1 at 2000 mA g-1 compared with CGH, CGH@C and CGH/rGO composites. Besides, the reversible capacity of 266 mA h g-1 still remained even after 500 cycles at current density of 1 A g-1. Such outstanding electrochemical performance could be accredited to a strong interaction between CGH, carbon, and graphene, which increases the electronic conductivity, relieves the volume expansion aroused by sodiation/desodiation, shortens the pathway of electron/ion transportation that further improving the reaction kinetics and endowing the material with remarkable cycling capability. Obviously, this in situ hydrothermal synthesis of double carbon coating strategy can be extended to designing other candidates of anode materials for SIBs.

Electrochemically Induced Structural and Morphological Evolutions in Nickel Vanadium Oxide Hydrate Nanobelts Enabling Fast Transport Kinetics for High-Performance Zinc Storage.

Suitable intercalation cathodes and fundamental insights into the Zn-ion storage mechanism are the crucial factors for the booming development of aqueous zinc-ion batteries. Herein, a novel nickel vanadium oxide hydrate (Ni0.25V2O5·0.88H2O) is synthesized and investigated as a high-performance electrode material, which delivers a reversible capacity of 418 mA h g-1 with 155 mA h g-1 retained at 20 A g-1 and a high capacity of 293 mA h g-1 in long-term cycling at 10 A g-1 with 77% retention after 10,000 cycles. More importantly, multistep phase transition and chemical-state change during intercalation/deintercalation of hydrated Zn2+ are illustrated in detail via in situ/ex situ analytical techniques to unveil the Zn2+ storage mechanism of the hydrated and layered vanadium oxide bronze. Furthermore, morphological development from nanobelts to hierarchical structures during rapid ion insertion and extraction is demonstrated and a self-hierarchical process is correspondingly proposed. The unique evolutions of structure and morphology, together with consequent fast Zn2+ transport kinetics, are of significance to the outstanding zinc storage capacity, which would enlighten the mechanism exploration of the aqueous rechargeable batteries and push development of vanadium-based cathode materials.

Detailed observation on expression dynamics of Polycomb group genes during rice early endosperm development in subspecies hybridization reveals their characteristics of parent-of-origin genes.

BACKGROUND: Parent-of-origin gene expression and its role in seed development have drown a great attention in recent years. Genome-wide analysis has identified hundreds of candidate imprinted genes, a major type of parent-of-origin genes, in rice hybrid endosperms at the stage of 5 days after pollination (dap). However, the expression of these genes in early endosperm have been never confirmed due to technique limitations and the behavior of the imprinted genes in different rice hybridizations are still largely unknown. RESULTS: Here, based on our elaborate technique established previously, the expression patterns of PcG genes in the early stages of endosperm development (within 3 dap), were comprehensively analyzed. We revealed that the free nucleus stage of endosperm development is critical for parent-of-origin gene analysis. The expression of the imprinted genes are highly dynamic, likely corresponding to the critical developmental events during this period. Hybridizations between Oryza sativa japonica and indica showed that the expression patterns of the same imprinted gene could be varied by crossing with different parental cultivars, indicative of their parent-dependent character. There are strong alleles that often showed predominant expression over other alleles regardless of the parental origin, which provides a possible explanation for the cultivar-dependent predominant phenotype in crop hybridizations. In addition, we found that the transcripts of the same gene behave differently, with imprinting or non-imprinting patterns, suggesting the existence of not only imprinted and non-imprinted genes but also imprinted or non-imprinted transcripts, which reveals new aspects of the genomic imprinting. CONCLUSIONS: These findings on the characters of parent-of-origin genes shed light on the understanding the real role of gene imprinting in endosperm development.

A 3D interconnected NH4Fe0.6V2.4O7.4@C nanocomposite with superior sodium storage properties.

A novel 3D interconnected NH4Fe0.6V2.4O7.4@C nanocomposite was in situ synthesized through a facile hydrothermal reaction at low temperature (98 °C), and its electrochemical performance as a cathode for sodium-ion batteries (SIBs) was investigated for the first time. Under the intercalation of Fe3+ and carbon-coating, as-prepared samples turned to 3D interconnected structures, which were composed of NH4Fe0.6V2.4O7.4 nanoparticles and carbon chains. The 3D interconnected NH4Fe0.6V2.4O7.4@0.5 wt%C nanocomposite exhibits a high discharge specific capacity of 306 mA h g-1 at a current density of 20 mA g-1 and a high-rate capacity of 130 mA h g-1 at 0.4 A g-1. The results of EIS and ex situ SEM indicated that the 3D interconnected NH4Fe0.6V2.4O7.4@0.5 wt%C nanocomposite possesses good electrical conductivity and structural stability. The ex situ XRD results suggest that NH4Fe0.6V2.4O7.4@0.5 wt%C undergoes a reversible insertion/de-insertion mechanism during a charge/discharge process. Our work demonstrates that the 3D interconnected NH4Fe0.6V2.4O7.4@C nanocomposite material could be considered as a potential cathode for sodium ion batteries.

Synthesis and structural data of a Fe-base sodium metaphosphate compound, NaFe(PO3)3.

This data article contains the synthesis and structure information of a new Fe-base sodium metaphosphate compound, which is related to the research article entitled 'Synthesis, structural, magnetic and sodium deinsertion/insertion properties of a sodium ferrous metaphosphate, NaFe(PO3)3' by Lin et al. [1]. The research article has reported a new Fe-base metaphosphate compound NaFe(PO3)3, which is discovered during the exploration of the new potential electrode materials for sodium-ion batteries. In this data article, the synthesized process of this metaphosphate compound and the morphology of the obtained sample will be provided. The high-power XRD Rietveld refinement is applied to determine the crystal structure of this metaphosphate compound and the refinement result including the main refinement parameters, atomic coordinate and some important lattace parameters are stored in the cif file. Also, the refined structure has be evaluated by checkcif report and the result is also provided as the supplementary materials.

The isolation of early nuclear endosperm of Oryza sativa to facilitate gene expression analysis and screening imprinted genes.

BACKGROUND: Since the quality and yield of rice production depends on endosperm development, previous studies have focused on the molecular mechanism that regulates this developmental process. Recently, how this process is epigenetically regulated has become an important topic. However, the gene expression analysis and screening imprinted genes during early endosperm development remain challenging since the isolation of early endosperm has not been possible. Here, we report a procedure for the isolation of endosperm at 24 or 48 HAP (hours after pollination) during the free nuclear stage of endosperm development. RESULTS: This technique allows for rapid and convenient collection of pure free nuclear endosperm. Early endosperm RNA can then be extracted from the isolated endosperm cells using dynabeads. Our results showed that the quality of RNA is satisfactory for gene expression analysis and screening the parental-of-origin specific genes in early endosperm. CONCLUSIONS: Thus, we offer a reliable method to overcome one of the major obstacles in the investigation of the molecular mechanisms of early endosperm development. Our approach can be used for accurate gene expression analysis and screening of imprinted genes, and facilitates the confirmation of endosperm-specific gene expression at the very early stages of endosperm development. This method could also be used in other species to collect early free nuclear endosperm.