Cytological mechanisms of interspecific incrossability and hybrid sterility between Oryza sativa L. and O. alta Swallen

Oryza sativa and O. alta belong to AA and CCDD genomes in Oryza, respectively. Interspecific repro-ductive isolation limits the transfer of favorable genes from O. alta into O. sativa. The cytological mechanisms of interspecific incrossability and hybrid sterility between O. sativa and O. alta were studied systematically in this paper. We indentified two cytological causes of interspecific incrossabil-ity. First, we observed embryo sac incompatibility that caused fertilization barriers of variable severity such as non-fertilization, fertilization stagnation and egg cell single-fertilization. Second, we observed hybrid inviability, the major cause for incrossability, apparent from hybrid embryo developmental stagnation and embryo abortion. Hybrid sterility included both embryo sac sterility and pollen sterility. The hybrid embryo sac was completely sterile and exhibited mainly embryo sac degeneration. Hybrid pollen was also sterile and mainly typical abortive. Hybrid sterility was mainly caused by severely ab-normal meioses of megasporocytes and pollen mother cells; it is the most important abnormality, being chromosome sterility. Several methods are suggested to overcome the interspecific reproductive iso-lation between O. sativa and O. alta.     

A guided tour: Pollen tube orientation in flowering plants

Sexual reproduction in flowering plants requires that two sperm cells are delivered to the embryo sac where double fertilization of an egg cell and of a central cell results in the formation of a diploid embryo and of the triploid nutritional endosperm tissue. The immobile male gametes are delivered to the im- mobile female gametophyte by a single cell, the pollen tube. The pollen tube must be able to germinate on a genetically appropriate stigma and it must be directed through the transmitting tract of the style from where it must target an ovule. Moreover, the pollen tube must enter the ovule at a defined opening, the micropyle, grow toward one of the two synergids and release the two sperm cells upon contact. This complex process requires recognition events with chemically based or physically supported cell-cell communication as well as directional cues for the growing pollen tube. A number of molecules and mechanisms have been implicated in pollen tube guidance which are summarized in this review.     

Hypoosmotic shock induces a stateⅠtransition of photosynthetic apparatus in Dunaliella salina

The effects of hypoosmotic shock on state transition in darkness in Dunaliella salina were studied. When the concentration of NaCI in culture medium was dropped from 1.5 to 0.5 mol/L abruptly, the photosynthetic rate of D.salina declined, but the respiratory rate and intracellular ATP content increased in the dark. The FpsⅡ/FpsⅠ ratio at 77 K of D. salina cells exposed to hypoosmotic shock was higher than that of control cells, indicating that more excitation energy was distributed to PS Ⅱ in stressed D.salina cells upon illumination. A decrease in LHC Ⅱ phosphorylation level was also observed when D.salina was exposed to hypoosmotic shock. Thus a state Ⅰ transition of photosynthetic apparatus occurs when D.salina suffers hypoosmotic shock in darkness, which is supposed to be related to an enhancement of respiration and an increase in ATP content in stressed D.salina cells.     

Antisense expression of a rice cellular apoptosis susceptibility gene (OsCAS} alters the height of transgenic rice

Cellular apoptosis susceptibility (CAS) gene plays important roles in mitosis, development and export of importin a from the nucleus, but its function in plant is unknown. In this study, a rice CAS ortholog (OsCAS), which encodes a predicted protein of 983 amino acids with 62% similarity to human CAS, was identified. DNA gel blot analysis revealed a single copy of OsCAS in the rice genome. A 973 bp fragment at the 3' end of OsCAS cDNA was cloned from rice cDNA library and transferred into rice in the antisense direction under the control of CaMV 35S promoter via Agrobacterium-mediated transformation method, 105 transgenic lines were obtained. Expression of OsCAS was suppressed in the antisense transgenic lines as revealed by semi-quantitative RT-PCR. The antisense transgenic lines showed dwarf phenotypes. The results indicated that OsCAS was involved in culm development of rice.     

Antisense expression of a rice cellular apoptosis susceptibility gene (OsCAS) alters the height of transgenic rice

Cellular apoptosis susceptibility (CAS) gene plays important roles in mitosis, development and export of importin α from the nucleus, but its function in plant is unknown. In this study, a rice CAS ortholog (OsCAS), which encodes a predicted protein of 983 amino acids with 62% similarity to human CAS, was identified. DNA gel blot analysis revealed a single copy of OsCAS in the rice genome. A 973 bp fragment at the 3′ end of OsCAS cDNA was cloned from rice cDNA library and transferred into rice in the antisense direction under the control of CaMV 35S promoter via Agrobacterium-mediated transformation method, 105 transgenic lines were obtained. Expression of OsCAS was suppressed in the antisense transgenic lines as revealed by semi-quantitative RT-PCR. The antisense transgenic lines showed dwarf phenotypes. The results indicated that OsCAS was involved in culm development of rice.     

Characteristics of the short rachillae of rice from archaeological sites dating to 7000 years ago

The abscission layer formed on a pedicel situated at the basal part of a short rachilla is an important characteristic for discriminating between wild, japonica, and indica rice. The short rachillae of paddy rice grains excavated from the Kuahuqiao, Luojiajiao, and Tianluoshan sites, located in the lower reaches of the Yangtze River and dating to 7000 years old, were observed. The results showed that the short rachillae could be divided into two types: a wild type and japonica type. These results indicated that the rice had been domesticated, but was a primitive cultivated rice that retained some of the characteristics of wild rice. The results also suggested that the rice was changing to resemble japonica type rice. Based on the ratios of wild and japonica types, it was inferred that rice domestication began 10000 years ago.     

Splicing-site recognition of rice （Oryza sativa L. ） DNA sequences by support vector machines

Motivation: It was found that high accuracy splicing-site recognition of rice ( Oryza satlva L. ) DNA sequence is especially difficult. We described a new method for the splicing-site recognition of rice DNA sequences. Method: Based on the intron in eukaryotic organisms conforming to the principle of GT-AG, we used support vector machines (SVM) to predict the splicing sites. By machine learning, we built a model and used it to test the effect of the test data set of true and pseudo splicing sites. Results : The prediction accuracy we obtained was 87.53% at the true 5‘ end splicing site and 87.37% at the true 3‘ end splicing sites. The results suggested that the SVM approach could achieve higher accuracy than the previous approaches.     

Location of the protein of<Emphasis Type="Italic">RSG</Emphasis>6, a predominantly expressed gene in rice sperm cells

Using Western blot and immunohistochemistry analysis, here the localization of RSC-6 protein was determined in various tissues of rice. Western blot showed only a weak signal in mature pollen. Nevertheless, according to the result of immunohistochemistry with DAB and fluorescent staining, the expression of RSC-6 protein appeared to begin at the bicellular microspore stage, and then keep activity in the sperm cells of mature pollens. The fluorescence patternshowed RSC-6 polypeptide was present close to or attached to the surface of the isolated sperm cells. And this suggested that RSG6 might take an important part in the process of recognition of sperm cell and ovum.     

三价砷存在条件下毒砂表面微结构对热氧化硫杆菌附着性的影响

Understanding bacterial adsorption and the evolution of biofilms on arsenopyrite with different surface structures is of great significance to clarifying the mechanism of microbe–mineral interfacial interactions and the production of acidic mine drainage impacting the environment. In this study, the attachment of Sulfobacillus thermosulfidooxidans cells and subsequent biofilm formation on arsenopyrite with different surface structures in the presence of dissolved As(Ⅲ) was studied. Arsenopyrite slices with a specific surface were obtained by electrochemical corrosion at 0.26 V. The scanning electronic microscopy-energy dispersion spectra analyses indicated that the arsenopyrite surface deficient in sulfur and iron obtained by electrochemical treatment was not favorable for the initial adsorption of bacteria, and the addition of As(Ⅲ) inhibited the adsorption of microbial cells. Epifluorescence microscopy showed that the number of cells attaching to the arsenopyrite surface increased with time; however, biofilm formation was delayed significantly when As(Ⅲ) was added.     

Grain boundary segregation of minor arsenic and nitrogen at elevated temperatures in a microalloyed steel

Auger electron spectroscopy (AES) was used to investigate the grain boundary segregation of arsenic and nitrogen in a kind of microalloyed steel produced by a compact strip production (CSP) technology at 950 to 1100℃, which are similar to the hot working temperature of the steel on a CSP production line. It was discovered that arsenic segregated on grain boundaries when the steel was annealed at 950℃ for 2 h. When the annealing temperature increased to 1100℃, arsenic was also found to have segregated on grain boundaries in the early annealing stage, for instance, within the first 5 min annealing time. However, if the holding time of the steel at this temperature increased to 2 h, arsenic diffused away from grain boundaries into the matrix again. Nitrogen was not found to have segregated on grain boundaries when the steel was annealed at a relatively low temperature, such as 950℃. But when the annealing temperature increased to 1100℃, nitrogen was detected to have segregated at grain boundaries in the steel.     

Effect of the surface microstructure of arsenopyrite on the attachment of Sulfobacillus thermosulfidooxidans in the presence of dissolved As(Ⅲ)

Understanding bacterial adsorption and the evolution of biofilms on arsenopyrite with different surface structures is of great significance to clarifying the mechanism of microbe–mineral interfacial interactions and the production of acidic mine drainage impacting the environment. In this study, the attachment of Sulfobacillus thermosulfidooxidans cells and subsequent biofilm formation on arsenopyrite with different surface structures in the presence of dissolved As(Ⅲ) was studied. Arsenopyrite slices with a specific surface were obtained by electrochemical corrosion at 0.26 V. The scanning electronic microscopy-energy dispersion spectra analyses indicated that the arsenopyrite surface deficient in sulfur and iron obtained by electrochemical treatment was not favorable for the initial adsorption of bacteria, and the addition of As(Ⅲ) inhibited the adsorption of microbial cells. Epifluorescence microscopy showed that the number of cells attaching to the arsenopyrite surface increased with time; however, biofilm formation was delayed significantly when As(Ⅲ) was added.     

Corrosion of magnesium and magnesium –calcium alloy in biologically-simulated environment

A study of biocompatibility and corrosion of both metallic magnesium(Mg) and a magnesium alloy containing 1% calcium(Mg–Ca) were investigated in in vitro culture conditions with and without the presence of bone marrow derived human mesenchymal stem cells(h MSCs).Chemical analysis of the degraded samples was performed using XRD and FEGSEM. The results from the XRD analysis strongly suggested that crystalline phase of magnesium carbonate was present on the surface of both the Mg and Mg–Ca samples. Flame absorption spectrometry was used to analyse the release of magnesium and calcium ions into the cell culture medium. Magnesium concentration was kept consistently at a level ranging from 40 to 80 m M for both Mg and Mg–Ca samples. No cell growth was observed when in direct contact with the metals apart from a few cells observed at the bottom of culture plate containing Mg–Ca alloy. In general, in vitro study of corrosion of Mg–Ca in a biologicallysimulated environment using cell culture medium with the presence of h MSCs demonstrated close resemblances to in vivo corrosion. Although in vitro corrosion of Mg–Ca revealed slow corrosion rate and no immediate cytotoxicity effects to h MSCs, its corrosion rate was still too high to achieve normal stem cell growth when cells and alloys were cultured in vitro in direct contact.     

Promoter of soybean early nodulin gene<Emphasis Type="Italic">enod2B</Emphasis> is induced by rhizobial Nod factors in transgenic rice

Nod factors, which are signaling molecules produced by Rhizobia, are the principal determinants of host specificity in Rhizobium-legume symbiosis. Nod factors can elicit a number of characteristic developmental responses in the roots of legumes, such as depolarization of the membrane potential in epidermal cells, specific expression of early nodulin genes and changes in the flux of calcium in root hairs, deformation of root hairs, cell division in the root cortex and formation of the nodule primordinm. Whether the rice plant can respond to signaling molecules (i.e. Nod factors) is an important question, as it could establish the potential for symbiotic nitrogen fixation in rice. The promoter of the soybean (Glycine max) early nodulin gene Gmenod2B fused to the β-glucuronidase (GUS) reporter gene was used as a molecular marker to explore whether Nod factors can be recognized by rice cells as signaling molecules. Transgenic rice plants harboring the chimeric gene Gmenod2BP-GUS were obtained via an Agrobacterium tumefaciens-mediated system. NodNGR factors produced by a broad-host-range Rhizobium strain NGR234(pA28) were used as probes to investigate the activity of the Gmenod2B promoter in rice. Our results showed that the early nodulin gene Gmenod2B promoter was induced by NodNGR factors in transgenic rice, and that it was specifically expressed in rice plant roots. Moreover, GUS gene expression driven by the Gmenod2B promoter in transgenic rice was regulated by nitrogen status. These findings indicated that rice possessed the ability to respond to Nod factor signals, and that this signal transduction system resulted in activation of the Gmenod2B promoter. Thus, we predict that the Nod-factor inducible nodulin expression system, which is similar to Rhizobium-legume symbiosis, may also exist in rice.     

DEM/CFD modelling of the deposition of dilute granular systems in a vertical container

Deposition of granular materials into a container is a general industrial packing process. In this study, the deposition behaviour of dilute granular mixtures consisting of two types of particles that were of the same particle size but different particle densities in the presence of air was numerically analyzed using a coupled discrete element method （DEM） and computational fluid dynamics （CFD）. Bilayer granular mixtures with light particles at bottom and heavy particles at top were first simulated. It was found that the presence of air significantly affected the flow behaviour of the bilayer mixtures. For the system with a relatively low initial void fraction, the air entrapped inside the container escaped through the dilated zones induced due to the friction between the powder bed and wall surfaces. The escaping air streams entrained light particles that were originally located at the bottom of the granular system. Consequently, these light particles were migrated to the top of the granular bed at the end of deposition process. More light particles were migrated when the deposition distance was increased. For the system with a high initial void fraction, some light particles penetrated into the top layer of heavy particles and created a mixing zone. Deposition of random mixtures with different initial void fractions was also investigated and the influence of initial void fraction on the segregation behaviour was explored as well. It was found that the increase of void fraction promoted segregation during the deposition in air. It was demonstrated that, for granular mixtures consisting of particles of different air sensitivities, the presence of air had a significant impact on the mixing and segregation behaviour during the deposition.     

The induction of Sinorhizobium meliloti C4-dicarboxylate transport system （Dct） is regulated by oxygen concentration

The Sinorhizobium meliloti C4-dicarboxylate transport （Dct） system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate permease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is absolutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5a strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc- curred only at a certain depth under the surface of M63-0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentrations, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regulated by oxygen concentration.     

Open-air traveling-wave thermoacoustic generator

Taking the input and reflected waves into account,the relationship between the acoustic impedance at the end and the input of a system were theoretically analyzed.Closed and open acoustic configurations that influence the pressure,volumetric velocity,impedance and acoustic work were compared in detail.Based on the above investigation,an open-air traveling-wave thermoacoustic generator was designed and fabricated.It is composed of a looped tube,a resonator open at one end,a regenerator,and hot and cold heat exchangers.It is a small scale and simple configuration.The resonant frequency is 74 Hz at 1 bar in air.The maximum acoustic pressures at the open end and 0.5 m far away from the open end are 133.4 dB and 101 dB from a reference value of 20μPa when the heating power was 210 W,respectively.Acoustic pressure is reasonable for practical application as a low-frequency acoustic source.In further work,we believe that the acoustic pressure at the open end can achieve 150 dB,which could be a solution to problems in existing acoustic generators.These problems include low acoustic pressure and system complexity.It can be used as a basic acoustic source for low frequency and long-range noise experiments,and as a supply for high acoustic pressures necessary for industrial sources.     

Genetic analysis and gene cloning of a triangular hull 1 (tri1) mutant in rice (Oryza sativa L.)

Grain shape and size are two key factors that determine rice yield and quality. In the present study, a rice triangular hull mutant (tri1) was obtained from the progeny of japonica rice variety Taipei 309 treated with 60Co γ-rays. Compared to the wild type, the tri1 mutant presents a triangular hull, and exhibits an increase in grain thickness and protein content, but with a slight decrease in plant height and grain weight. Genetic analysis indicated that the mutant phenotype was controlled by a recessive nuclear gene which is stably inherited. Using a map-based cloning strategy, we fine-mapped tri1 to a 47-kb region between the molecular markers CHR0122 and CHR0127 on the long arm of chromosome 1, and showed that it co-segregates with the molecular marker CHR0119. According to the rice genome sequence annotation there are six predicated genes within the mapped region. Sequencing analysis of the mutant and the wild type indicated that there was a deletion of an A nucleotide in exon 3 of the OsMADS32 gene, which could result in a downstream frameshift mutation and premature termination of the predicted polypeptide. Both semi-quantitative and real-time RT-PCR analyses showed that this gene expressed highly in young inflorescences, while expressed at very low levels in other tissues. These results implied that the OsMADS32 gene could be a candidate of TRI1. Taken together, the results of this study lay the foundation for further investigation into the molecular mechanisms regulating rice caryopsis development.     

A simple and effective method for total RNA isolation of appressoria in Magnaporthe oryzae

Appressorium formation is an important event in establishing a successful interaction between the rice blast fungus, Magnaporthe oryzae, and its host plant, rice. An understanding of molecular events occurring in appressorium differentiation will give new strategies to control rice blast. A quick and reliable method to extract total RNA from appressorium is essential for studying gene expression during appressorium formation and its mechanism. We found that duplicate film is an efficient substratum for appressorium formation, even when inoculated with high density conidia. When inoculated with conidia at 1 × 106 ml^-1, the percentages of conidium germination and appressorium formation were （97.98±0.67）% and （97.88±0.45）%, respectively. We applied Trizol before appressorium collection for total RNA isolation, and as much as 113.6 lag total RNA was isolated from the mature appressoria at 24 h after inoculation. Functional analysis of two genes, MNH6 and MgATG1, isolated from the cDNA subtractive library, revealed that the quantity of RNA was good enough to construct a cDNA （complementary DNA） library or a cDNA subtractive library. This method may be also applicable for the appressorium RNA isolation of other pathogenic fungi in which conidia differentiate into appressoria in the early stages of host infection.     

Developmental characteristics and response to iron toxicity of root border cells in rice seedlings

To investigate the Fe^2＋ effects on root tips in rice plant, experiments were carried out using border cells in vitro. The border cells were pre-planted in aeroponic culture and detached from root tips. Most border cells have a long elliptical shape. The number and the viability of border cells in situ reached the maxima of 1600 and 97.5%, respectively, at 20---25 mm root length. This mortality was more pronounced at the first 1-12 h exposure to 250 mg/L Fe^2＋ than at the last 12-36 h. After 36 h, the cell viability exposed to 250 mg/L Fe^2＋ decreased to nought, whereas it was 46.5% at 0 mg/L Fe^2＋. Increased Fe^2＋ dosage stimulated the death of detached border cells from rice cultivars. After 4 h Fe^2＋ treatment, the cell viabilities were _〉80% at 0 and 50 mg/L Fe^2＋ treatment and were 〈62% at 150, 250 and 350 mg/L Fe^2＋ treatment; The viability of border cells decreased by 10% when the Fe^2＋ concentration increased by 100 mg/L. After 24 h Fe^2＋ treatment, the viabilities of border cells at all the Fe^2＋ levels were 〈65%; The viability of border cells decreased by 20% when the Fee＋ concentration increased by 100 mg/L. The decreased viabilities of border cells indicated that Fe^2＋ dosage and treatment time would cause deadly effect on the border cells. The increased cell death could protect the root tips from toxic harm. Therefore, it may protect root from the damage caused by harmful iron toxicity.