Chengzhen Liang

Catalytic synthesis and photoluminescence of β-Ga2O3 nanowires

Monoclinic gallium oxide (β-Ga2O3) nanowires were synthesized by heat treating a composite material of GaAs and pre-evaporated Au at 1240 °C in dry oxygen atmosphere. The catalytic Au metal generated liquid nanoclusters that serve as reactive sites confining and directing the growth of β-Ga2O3 nanowires during the vapor-liquid-solid growth process. The β-Ga2O3 nanowires have diameters ranging from 20 to 50 nm and lengths of several micrometers. Photoluminescence measurement under excitation at 250 nm shows that the bulk β-Ga2O3 nanowires have a stable blue emission at 475 nm and an ultraviolet emission at 330 nm, which may be related to the defects such as the oxygen vacancy and the gallium–oxygen vacancy pair.

OsNAP connects abscisic acid and leaf senescence by fine-tuning abscisic acid biosynthesis and directly targeting senescence-associated genes in rice

Significance Premature leaf senescence is known to decrease rice yield severely, but the molecular mechanism underlying this relationship remains largely unknown. Similarly, although abscisic acid (ABA)-induced leaf senescence has long been observed, the mechanism of this pathway has yet to be determined. In this study we identified and characterized a dominant premature leaf senescence mutant, prematurely senile 1 (ps1-D). The data demonstrated both that PS1/Oryza sativa NAC (no apical meristem, Arabidopsis ATAF1/2, and cup-shaped cotyledon2)-like, activated by apetala3/pistillata (OsNAP) is an ideal marker of natural senescence onset and that it functions as an important link between ABA and leaf senescence in rice. Furthermore, reduced OsNAP expression led to extended grain filling and an improved seed-setting rate, which significantly enhanced the grain yield. Thus, fine-tuning OsNAP expression should be a means of improving rice yield. It has long been established that premature leaf senescence negatively impacts the yield stability of rice, but the underlying molecular mechanism driving this relationship remains largely unknown. Here, we identified a dominant premature leaf senescence mutant, prematurely senile 1 (ps1-D). PS1 encodes a plant-specific NAC (no apical meristem, Arabidopsis ATAF1/2, and cup-shaped cotyledon2) transcriptional activator, Oryza sativa NAC-like, activated by apetala3/pistillata (OsNAP). Overexpression of OsNAP significantly promoted senescence, whereas knockdown of OsNAP produced a marked delay of senescence, confirming the role of this gene in the development of rice senescence. OsNAP expression was tightly linked with the onset of leaf senescence in an age-dependent manner. Similarly, ChIP-PCR and yeast one-hybrid assays demonstrated that OsNAP positively regulates leaf senescence by directly targeting genes related to chlorophyll degradation and nutrient transport and other genes associated with senescence, suggesting that OsNAP is an ideal marker of senescence onset in rice. Further analysis determined that OsNAP is induced specifically by abscisic acid (ABA), whereas its expression is repressed in both aba1 and aba2, two ABA biosynthetic mutants. Moreover, ABA content is reduced significantly in ps1-D mutants, indicating a feedback repression of OsNAP on ABA biosynthesis. Our data suggest that OsNAP serves as an important link between ABA and leaf senescence. Additionally, reduced OsNAP expression leads to delayed leaf senescence and an extended grain-filling period, resulting in a 6.3% and 10.3% increase in the grain yield of two independent representative RNAi lines, respectively. Thus, fine-tuning OsNAP expression should be a useful strategy for improving rice yield in the future.

Large-scale synthesis of β-SiC nanowires by using mesoporous silica embedded with Fe nanoparticles

Abstract A novel method has been developed to produce bulk quantities of β-SiC nanowires from the mixture of activated carbon and sol–gel derived silica embedded with Fe nanoparticles. Detailed investigation with X-ray diffraction, transmission electron microscopy, energy-dispersed X-ray and high-resolution transmission electron microscopy confirm that the nanowires consist of a 10–30 nm diameter single crystalline core wrapped with an amorphous silicon oxide layer, and have length up to several tens of micrometers. The formation process of β-SiC nanowires involves carbothermal reduction and a vapor–liquid–solid growth process. Two broad photoluminescence peaks located around 340 and 440 nm were observed at room temperature.

Variation in NRT1.1B contributes to nitrate-use divergence between rice subspecies

Asian cultivated rice (Oryza sativa L.) consists of two main subspecies, indica and japonica. Indica has higher nitrate-absorption activity than japonica, but the molecular mechanisms underlying that activity remain elusive. Here we show that variation in a nitrate-transporter gene, NRT1.1B (OsNPF6.5), may contribute to this divergence in nitrate use. Phylogenetic analysis revealed that NRT1.1B diverges between indica and japonica. NRT1.1B-indica variation was associated with enhanced nitrate uptake and root-to-shoot transport and upregulated expression of nitrate-responsive genes. The selection signature of NRT1.1B-indica suggests that nitrate-use divergence occurred during rice domestication. Notably, field tests with near-isogenic and transgenic lines confirmed that the japonica variety carrying the NRT1.1B-indica allele had significantly improved grain yield and nitrogen-use efficiency (NUE) compared to the variety without that allele. Our results show that variation in NRT1.1B largely explains nitrate-use divergence between indica and japonica and that NRT1.1B-indica can potentially improve the NUE of japonica.

Preparation and characterization of amorphous SiOx nanowires

Abstract Large-scale synthesis of amorphous silicon oxide nanowires (SiONWs) was achieved by using simple physical evaporation of the mixture of silica xerogel containing Fe nanoparticles and silicon powder. Transmission electron microscopy (TEM) observations showed that the amorphous SiONWs have a length of up to several tens of micrometers and a diameter of 10–40 nm. Energy-dispersed X-ray spectrometry (EDX) analysis revealed that the SiONWs consist of Si and O elements in atomic ratio approximately to 1:1.4. Different morphologies of nanowires such as straight, smoothly curved, braided and helical shapes were observed. The formation process of SiONWs was closely related to the VLS growth mechanism. Raman scattering spectrum of amorphous SiONWs showed that there is an asymmetric, broadened linewidth Raman peak at 502 cm −1 greatly different from that of bulk SiO 2 non-crystalline solids.

Melatonin delays leaf senescence and enhances salt stress tolerance in rice

Melatonin, an antioxidant in both animals and plants, has been reported to have beneficial effects on the aging process. It was also suggested to play a role in extending longevity and enhancing abiotic stress resistance in plant. In this study, we demonstrate that melatonin acts as a potent agent to delay leaf senescence and cell death in rice. Treatments with melatonin significantly reduced chlorophyll degradation, suppressed the transcripts of senescence‐associated genes, delayed the leaf senescence, and enhanced salt stress tolerance. Genome‐wide expression profiling by RNA sequencing reveals that melatonin is a potent free radical scavenger, and its exogenous application results in enhanced antioxidant protection. Leaf cell death in noe1, a mutant with over‐produced H2O2, can be relieved by exogenous application of melatonin. These data demonstrate that melatonin delays the leaf senescence and cell death and also enhances abiotic stress tolerance via directly or indirectly counteracting the cellular accumulation of H2O2.

Synthesis of gold nanoparticles dispersed within pores of mesoporous silica induced by ultrasonic irradiation and its characterization

Abstract Gold (Au) nanoparticles loaded within pores of mesoporous silica were in situ synthesized by sonochemical reduction of chloroauric acid (HAuCl 4 ) within pores of silica. The sonochemical reduction was carried out by ultrasonic irradiation in argon atmosphere at room temperature. The composite was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HREM) techniques. It has been shown that nearly spherical shaped Au nanoparticles, with a fairly narrow size distribution, are isolated from each other and uniformly dispersed within the pores, which are less than 9 nm in diameter. With the decrease of particles size, a significant red-shift of surface plasma resonance (SPR) band of Au particles was observed in the optical absorption measurement.

Preparation and characterization of CdS nanoparticles by ultrasonic irradiation

Abstract Cadmium sulfide (CdS) nanoparticles of about 3 nm in diameter have been prepared by the sonochemical reduction of a mixed solution of cadmium chloride (CdCl2), sodium thiosulfate (Na2S2O3) and isopropyl alcohol ((CH3)2CHOH) in Ar atmosphere at room temperature. The CdS nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The formation mechanism of CdS nanoparticles is also discussed together with the optical absorption spectroscopy analysis. The method presented here can be used for the preparation of other sulfide nanoparticles.

Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice.

Significance As one of the most important growth-promoting hormones, auxin regulates many aspects of plant growth and development. Understanding auxin action has long been a challenging task because of the complexity of the hormone transport involved in auxin response. Despite tremendous progress made in Arabidopsis, auxin response and transport are poorly understood in crop plants, which impedes the application of hormone knowledge in agricultural improvement. This study not only identifies a novel positive regulator of plant growth in rice and demonstrates its significant role in improving seed size and grain yield, it also illustrates the specific involvement of the plasma membrane-associated protein in regulating auxin response and transport, thus illuminating a new strategy for enhancing crop productivity. Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity.

A facile synthesis route to CdS nanocrystals at room temperature

CdS nanocrystals have been prepared by a sonochemical reduction of a mixed solution of CdCl , Na S O and 22 2 3 Ž. CH CHOH in Ar atmosphere at room temperature. The products were characterized by X-ray diffraction, transmission 32 electron microscopy and X-ray photoelectron spectrum. It was found that the CdS nanocrystal is in b-CdS structure with an average size of about 5.5 nm in diameter, and the size distribution is very narrow. The chemical mechanism for the formation of CdS nanocrystals is discussed. q 2001 Elsevier Science B.V. All rights reserved.