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RNA interference (RNAi) is an RNA-dependent gene silencing process that is regulated by the interaction between the RNA-induced silencing complex (RISC) and double-stranded RNA (dsRNA). Exogenous dsRNAs are imported directly into the cytoplasm, where they are cleaved by Dicer into short dsRNA fragments of 20–25 base pairs. These short dsRNA fragments, called small interfering RNAs (siRNAs) have sequence-specific interaction with target genes. The guide strand, onto which siRNAs are incorporated in the RISC interacts with the target mRNA sequence, thereby inducing cleavage and degradation of target messenger RNAs (mRNAs) by ribonucleases. Recent studies have shown that plant dsRNA treatments can induce RNAi. However, the dsRNA application methods and delivery systems involved have not been well examined. In this study, dsRNA was introduced to Arabidopsis thaliana by two methods: dipping and spray. We synthesized two dsRNAs designed to target mRNAs encoding enhanced green fluorescent protein (EGFP). After applying dsRNAs that target EGFP, we found an obvious reduction in GFP expression. This was determined using fluorescence microscopy and quantitative reverse transcription PCR to assess the mRNA levels of the auxin-sensitive reporter DR5-EGFP Arabidopsis thaliana. Our data revealed that applying target gene-specific exogenous dsRNAs can induce suppression of target genes of interest whether the dipping or spray method is used. This study therefore provides a foundation for understanding how to apply and deliver dsRNAs in plants.

Plant chloride channels (CLCs) localize to the plasma and organellar membranes; these channels play pivotal roles in the modulation of ion homeostasis and cell turgor. Recent studies have shown that the expression of CLCs is involved in plant responses to environmental stress. Here, we examined the rice (Oryza sativa) tonoplast-localized channel OsCLC1. OsCLC1 is preferentially expressed in roots, and therefore, we generated transgenic rice with root-specific overexpression of OsCLC1 (RCc3::OsCLC1). We also identified a T-DNA mutant line that lacks expression of OsCLC1 (osclc1). We found that RCc3::OsCLC1 rice plants showed increased tiller number and grain yield, whereas the osclc1 plants exhibited decreased tiller number and grain yield, compared with wild type. These observations suggest that expression of OsCLC1 affects rice growth and productivity. Furthermore, RCc3::OsCLC1 plants showed enhanced drought tolerance, leading to increased grain yield compared to wild-type plants grown under the same conditions. By contrast, osclc1 mutants exhibited reduced drought tolerance and productivity compared to wild-type plants. When expression of OsCLC1 was analyzed in drought, jasmonic acid (JA) or abscisic acid (ABA)-treated rice, expression of OsCLC1 was preferentially upregulated in roots in response to drought and JA, and was preferentially upregulated in shoots in response to ABA. Together with the finding that expression of OsCLC1 is positively correlated both with expressions of OsDREB1A and OsbHLH148, key transcription factors in drought and JA responses, respectively, these results suggest that OsCLC1 regulates drought tolerance in rice and JA signaling is involved in this process.

Developmental flexibility under stress conditions largely relies on the interactions between hormones that mediate stress responses and developmental processes. In this study, we showed that the stress hormone jasmonic acid (JA) induces formation of extra xylem in the roots of wild-type Arabidopsis thaliana (Col-0). JA signaling mutants such as coronatine insensitive1-1 and jasmonate resistant1-1 did not form extra xylem in response to JA, but the JA biosynthesis mutant oxophytodienoate-reductase3 did form extra xylem. These observations suggested that the JA response promotes xylem development. To understand the mechanism, we examined the regulatory interaction between JA and cytokinin, a negative regulator of xylem development. JA treatment reduced cytokinin responses in the vasculature, and exogenous cytokinin nullified the effect of JA on formation of extra xylem. A time-course experiment showed that suppression of cytokinin responses by JA does not occur rapidly, but the JA-mediated xylem phenotype is tightly linked to the suppression of the cytokinin response. Further analysis of arabidopsis histidine phosphotransfer protein6-1 and myc2-3 mutants revealed that the JA-responsive transcription factor MYC2 regulates the expression of AHP6 in response to JA and expression of AHP6 is involved in the JA-mediated xylem phenotype.

Regulation of photosynthetic gene expression by plastid-encoded RNA polymerase (PEP) is essential for chloroplast development. The activity of PEP largely relies on at least 12 PEP-associated proteins (PAPs) encoded in the nuclear genome of plant cells. A recent model proposed that these PAPs regulate the establishment of the PEP complex through broad PAP-PEP or PAP-PAP interactions. In this study, we identified the Arabidopsis (Arabidopsis thaliana) seedling-lethal mutant ptac10-1, which has defects in chloroplast development, and found that the mutant phenotype is caused by the suppression of PLASTID S1 RNA-BINDING DOMAIN PROTEIN (pTAC10/PAP3). Analysis of the heterozygous mutant and pTAC10-overexpressing transgenic plants indicated that the expression level of pTAC10 is tightly linked to chloroplast development. Characterization of the interaction of pTAC10 with PAPs revealed that pTAC10 interacts with other PAPs, such as FSD2, FSD3, TrxZ, pTAC7, and pTAC14, but it does not interact with PEP core enzymes, such as rpoA and rpoB. Analysis of pTAC10 interactions using truncated pTAC10 proteins showed that the pTAC10 carboxyl-terminal region downstream of the S1 domain is involved in the pTAC10-PAP interaction. Furthermore, overexpression of truncated pTAC10s lacking the C-terminal regions downstream of the S1 domain could not rescue the ptac10-1 mutant phenotype and induced an abnormal whitening phenotype in Columbia-0 plants. Our observations suggested that these pTAC10-PAP interactions are essential for the formation of the PEP complex and chloroplast development.

The jasmonic acid (JA) and gibberellic acid (GA) signaling pathways interact to coordinate stress responses and developmental processes. This coordination affects plant growth and yield, and is mediated by interactions between the repressors of each pathway, the JASMONATE ZIM-DOMAIN PROTEIN (JAZ) and DELLA proteins. In this study we attempted to identify rice (Oryza sativa) JAZs that interact with rice DELLAs such as SLENDER RICE 1 (SLR1). Analysis of protein–protein interactions showed that OsJAZ8 and OsJAZ9 interact with SLR1; OsJAZ9 also interacted with the SLR1-LIKE (SLRL) protein SLRL2. Based on this broader interaction, we explored the function of OsJAZ9 in JA and GA responses by analyzing transcript levels of the JA-responsive gene OsbHLH148 and the GA-responsive gene OsPIL14 in OsJAZ9-overexpressing (OsJAZ9-Ox) and osjaz9 mutant plants. OsbHLH148 and OsPIL14 encode key transcription factors controlling JA and GA responses, respectively, and JA and GA antagonistically regulate their expression. In OsJAZ9-Ox, the expression of OsbHLH148 was downregulated and the expression of OsPIL14 was upregulated. By contrast, in osjaz9 mutants, the expression of OsbHLH148 was upregulated and the expression of OsPIL14 was downregulated. These observations indicated that OsJAZ9 regulates both JA and GA responses in rice, and this finding was supported by the opposite expression patterns of OsDREB1s, downstream targets of OsbHLH148 and OsPIL14, in the OsJAZ9-Ox and osjaz9 plants. Together, these findings indicate that OsJAZ9 suppresses JA responses and promotes GA responses in rice, and the protein–protein interaction between OsJAZ9 and SLR1 is involved in the antagonistic interplay between JA and GA.

The present study aims to fabricate PZT piezoelectric ceramic sheets which perform at a high capacity in low electric fields for developing actuators with large displacement. This paper describes the fabrication procedures of PZT sheets and their results. As the results of XRD analysis and SEM observations of precalcined powders showed, 800°C was the appropriate calcination temperature for Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.65Tia0.35)O3 composition. Green sheets with uniform thickness distribution were fabricated by Doctor Blade process with slurries 2000-5000cp in viscosity. The size of the fabricated green sheets was 135±5μm and 50±2μm in thickness, 180mm in width, and 5m in length, with a density of 4.7-5.1 g/cm3. Additives, such as solvent, binder, plasticizer and dispersant were completely eliminated by heat treatment at 500°C. The PbO excess atmosphere sintering at 1000°C produced PZT sheets which have perovskite phases only, and were well densed.

The present study aims to improve the capacity of actuator materials by focussing on the properties of a single sheet. Thin Pb(Zr0.53Ti0.47)O3 and Pb(Nb2/3Ni1/3)0.55(Zr0.3Ti0.7)0.45O3 composition sheets (about 130μm in thickness) with large surface areas were fabricated and their properties were investigated. Green sheets with uniform thickness distribution were fabricated by the doctor blade with a slurry viscosity of 2000-5000cp. Additives such as solvent, binder, plasticizer and dispersant were completely eliminated by the heat treatment which was carried out at 500°C. The PbO excess atmosphere sintering at temperatures above 1050°C and 1200°C produced high density Pb(Zr0.53Ti0.47)O3 sheets with only perovskite phases, and Pb(Nb2/3Ni1/3)0.55 (Zr0.3Ti0.7)0.45O3 sheets with perovskite phases and traces of pyrochlore phase, respectively. The dielectric and piezoelectric properties of sintered sheets showed slightly lower values than those of bulk samples fabricated by typical powder processing; however, the sheets exhibited a relatively large displacement at low electric fields.

The characteristics of spark plasma sintering, a new method of powder processing, were investigated. Four systems of intermetallic compounds—Ti-Al, Ti-Al-Cr, Mo-Si, and Mo-Si-Nb—were fabricated, and the formation process of compounds, the formed phases, and the microstructure of samples were observed. During the sintering of all the compositions of mixed powders, most of the compounds were formed by combustion reaction which occurred at almost the same temperature as the conventional combustion reaction temperature. The fabricated samples were well densified, however, the relative densities of the Mo-Si samples were lower than the Ti-Al samples. Ultrasonic images show that no internal defects were found in any sample and the grain size became finer with the increase in the Cr content in the Ti-Al system and Nb content in the Mo-Si system. The formed phases of Ti:Al=1:1 composition samples were TiAl and Ti3Al phases, and Ti-Al added Cr samples consisted of TiAl, Ti3Al, Cr2Al, and Cr9Al17 phases. The sample synthesized with Mo:Si=1:2 mixed powders had only MoSi2 phases, and Mo-Si samples with added Nb consisted of four phases: MoSi2 with a small amount of Mo5Si3 phases in the matrix and Nb5Si3 with unreacted Nb for dispersed phases.

MoSi2 is one of the-most promising candidate for high-temperature structural materials because of its high melting points and excellent oxidation resistance. However, the low room temperature fracture toughness and ductility, etc. of MoSi2 still remains as major obstacles to potential high temperature structural applications. The fracture toughness of brittle matrix can be improved by the incorporation of a ductile second phase such as metallic Nb. The purpose of this study is to improve the room temperature fracture toughness and ductility of sintered MoSi2 and MoSi2/Nb composites respectively by densification, refining of microstructure and minimizing of interfacial reactions between matrix and Nb. These compound and composite are prepared by mechanical alloying(MA)-spark plasma sintering(SPS) process. The microstructures and material properties of these samples were investigated by optical microscopy, SEM, XRD, EPMA, microhardness measurement and 4-point bending test. The Vickers hardness, bending strength and fracture toughness increased with the incorporation of metallic Nb.

In this study, Mo-Si and Mo-Si-Nb system were fabricated by the pulse discharge pressure-combustion synthesis method (Nb was added into Mo-Si, in order to improve ductility at room temperature and high temperature strength). During the synthesis of Mo-Si and Mo-Si-Nb mixed powders, samples abruptly shrunk at 1323K. It is clear that combustion reaction occurred at this temperature and compounds were formed by combustion reaction. The relative density of fabricated samples was 96 to 98% and no internal defects were foundby ultrasound images in the samples. The formed phases of the fabricated samples were as follows;only MoSi2 phases were formed for Mo:Si=1:2 mixed powders, and, for the Nb added samples, MoSi2, Nb5Si3 and Mo5Si3 phases were formed and unreacted Nb remained. Young's modulus and the bending strength of fabricated samples showed similar results. Monolithic MoSi2 sample had the highest value of Young's modulus and bending strength, and for Nb added samples, Young's modulus and bending strength decreased with the increase in Nb content.

The aims of this study were to observe the microstructure and the tormed phases of Ti-Al intermetallic compound system composites made by spark plasma-combustion synthesis and to investigate the phase formation mechanism.During the spark plasma sintering of the Ti:Al=1:1 powders, combustion synthesis was indicated by the abruptly shringkage in sample volume at Al melting point. The microstructure and the formed phase of spark plasma-combustion synthesized composites varied according to Ti particle size. For example, TiAl3 phases were formed when 100μm Ti powders were used, and TiAl, Ti2Al and Ti3Al phases were formed when 10μm Ti powders were used (the sintering temperature was 973K). The formation mechanism of compounds using spark plasma sintering has two processes; combustion synthesis at Al melting point and diffusion in the high temperature region.

This study aims to fabricate Pb(Zr,Ti)O3 (PZT) piezoelectric ceramic fibers by extrusion with mixture of PZT powder and PZT sol. The added PZT sol in this study played a role as a binder; the sol changed into PZT crystalline during sintering, and removal process of additives before sintering was not required. To obtain PZT fibers, the condition of sol viscosity adjustment, the mixture ratio of powder and sol for fiber extrusion, and the sintering condition for obtaining polycrystalline fibers were investigated. PZT precursor solution was synthesized from lead acetate trihydrate, zirconium n-propoxide and titanium isopropoxide by reflux at 120 degree(s)C for 3 hours with 2-methoxyethanol. The appropriate adjustment of spinnable sol was achieved by the addition of acetic acid for suppressing the hydrolysis reaction and the curing sol at 80 degree(s)C for promoting the condensation of sol. Green fibers with diameter of about 300micrometers were successfully extruded from the mixture of PZT powder and sol. The extruded fibers sintered at 1200 degree(s)C had the microstructure with 2-6micrometers grains and had no pores or cracks. From the result of displacement behavior measurement, PZT fibers fabricated by firing at 1200 degree(s)C in this study were considered to have desired piezoelectric properties.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spark Plasma Activated Sintering, SPAS, is a newly developed sintering method for both metal and ceramic powders. An advantage of the SPAS is that a powder can be consolidated in a very short time within several hundreds seconds, because the powder is pressurized in a mold and is heated by direct electric resistance heating of the powder, using pulsative electric current. Another advantage of the SPAS is that the sintering temperature is lower than conventional sintering methods such as hot press and HIP. For instance, a titanium-aluminide powder has to be sintered at 1473K by HIP, while well sintered at 1223K by the SPAS. However, so called “sintering temperature” of the SPAS is usually measured at the mold in place of the powder itself, because direct measurement of the powder’s temperature is much difficult from a technical point of view. It is considered that the powder is heated more rapidly than the mold and therefore the heat flows from the powder to the mold during sintering. Consequently, a temperature distribution is generated in the powder and therefore “true sintering temperature” cannot be clear.