Silicon mediated redox homeostasis in the root-apex transition zone of rice plays a key role in aluminum tolerance.

The supply of silicon (Si) mitigates the aluminum (Al) toxicity on plant root growth, while the underlying mechanism remains unknown. Transition zone (TZ) emerges as the Al-toxicity target of plant root apex. The objective of the study was to evaluate the effect of Si on redox homeostasis in root-apex TZ of rice seedlings under Al stress. Si alleviated Al toxicity as revealed by promotion of root elongation and less Al accumulation. In Si-deprived plants, treatment with Al altered the normal distribution of superoxide anion (O2·-) and hydrogen peroxide (H2O2) in root tip. Al induced a significant increase of reactive oxygen species (ROS) in root-apex TZ, resulting in the peroxidation of membrane lipid and loss of plasma membrane integrity in root-apex TZ. However, Si greatly increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and enzymes involved in ascorbate-glutathione (AsA-GSH) cycle in root-apex TZ under Al stress, and enhanced AsA and GSH contents, which reduced ROS and callose contents, thereby reducing malondialdehyde (MDA) content and Evans blue uptake. These results allow to precise the changes of ROS in root-apex TZ after exposure to Al, and the positive role of Si in maintaining redox balance in root-apex TZ.

Performance enhancement of gas sensing by modification of molybdenum selenide nanosheets with metal nanoparticles.

In this paper, nanostructured molybdenum selenide (MoSe2) with composited phases are synthesized by hydrothermal method, and the products are modified by metal anoparticles to improve the gas sensing performance. Microstructure characterization shows that few layered 1T/2H-MoSe2nanosheets have been successfully prepared. Both the morphology and component of nanosheets could be tuned by the reaction parameters. It is shown the MoSe2-based nanomaterials have excellent selectivity to nitrogen dioxide (NO2) according to gas sensing properties measurement. The sensitivity of 1T/2H-MoSe2nanosheets modified by Cu nanoparticles is 17.73 (50 ppm NO2) at the optimal operating temperature, which is the highest compared with other samples. The sensors also exhibit rapid response/recovery time and high stability. The sensing mechanism of MoSe2nanosheets toward NO2is investigated based on the first-principles calculation. The results suggest the modification by metal nanoparticles could significantly improve the adsorption energy and charge transfer between gas molecule and MoSe2. This work demonstrates a promising guidance for the design of new NO2gas sensing materials and devices.

Performance Enhancement of Gas Sensing by Modification of Molybdenum Selenide Nanosheets with Metal Nanoparticles.

In this paper, nanostructured Molybdenum Selenide (MoSe2) with composited phases are synthesized by hydrothermal method, and the products are modified by metal anoparticles to improve the gas sensing performance. Microstructure characterization shows that few layered 1T/2H-MoSe2 nanosheets have been successfully prepared. Both the morphology and composition of nanosheets could be tuned by the reaction parameters. It is shown the MoSe2-based nanomaterials have excellent selectivity to Nitrogen dioxide (NO2) according to gas sensing properties measurement. The sensitivity of 1T/2H-MoSe2 nanosheets modified by Cu nanoparticles is 17.73 (50 ppm NO2) at the optimal operating temperature, which is the highest compared with other samples. The sensors also exhibit rapid response/recovery time and high stability. The sensing mechanism of MoSe2 nanosheets toward NO2 is investigated based on the first-principles calculation. The results suggest the modification by metal nanoparticles could significantly improve the adsorption energy and the charge transfer between gas molecule and MoSe2. This work demonstrates a promising guidance for the design of new NO2 gas sensing materials and devices.

Exogenous spermidine alleviates the adverse effects of aluminum toxicity on photosystem II through improved antioxidant system and endogenous polyamine contents.

Aluminum (Al) toxicity is a major yield-limiting factor for crops in acidic soils. In this work, we have investigated the potential role of spermidine (Spd) on Al toxicity in rice chloroplasts. Exogenous Spd markedly reduced Al concentration and elevated other nutrient elements such as Mn, Mg, Fe, K, Ca, and Mo in chloroplasts of Al-treated plants. Meanwhile, Spd further activated arginine decarboxylase (ADC) activity of key enzyme in polyamine (PA) synthesis, and enhanced PA contents in chloroplasts. Spd application dramatically addressed Al-induced chlorophyll (Chl) losses, inhibited thylakoid membrane protein complexes degradation, especially photosystem II (PSII), and significantly depressed the accumulations of superoxide radical (O2·-), hydrogen peroxide (H2O2), and malondialdehyde (MDA) in chloroplasts. Spd addition activated antioxidant enzyme activities and decreased soluble sugar content in chloroplasts compared with Al treatment alone. Spd not only reversed the inhibition of photosynthesis-related gene transcript levels induced by Al toxicity, but diminished the increased expression of Chl catabolism-related genes. Furthermore, Chl fluorescence analysis showed that Spd protected PSII reaction centers and photosynthetic electron transport chain under Al stress, thus improving photosynthetic performance. These results suggest that PAs are involved in Al tolerance in rice chloroplasts and can effectively protect the integrity and function of photosynthetic apparatus, especially PSII, by mitigating oxidative damage induced by Al toxicity.

Responses of photosynthetic properties and antioxidant enzymes in high-yield rice flag leaves to supplemental UV-B radiation during senescence stage.

Despite the increasing occurrence of ultraviolet-B (UV-B) radiation, its molecular mechanism is poorly documented in higher plants compared to other environmental stress. In present study, the influence of supplemental UV-B radiation on photosynthetic performance and antioxidant enzymes in rice (Oryza sativa L.) was investigated. Supplemental UV-B radiation reduced net photosynthetic rate in rice flag leaves during senescence stage. By means of the JIP-test, it was found that the potential of processing light energy through the photosynthetic machinery was slightly inhibited by the increased thermal dissipation. Furthermore, 18 thylakoid membrane protein spots were differentially expressed (5-fold or greater variation compared to the control) in supplemental UV-B-treated rice. These identified proteins were involved in various cellular responses and metabolic processes including photosynthesis, stress defense, Calvin cycle, and others of unknown functions. Taken together, these results suggested that physiological changes that resulted from supplemental UV-B radiation were linked to the light reaction, carbon metabolism, and antioxidant enzymes in rice leaves during senescence stage.

Photosynthetic responses of Oryza sativa L. seedlings to cadmium stress: physiological, biochemical and ultrastructural analyses.

In the present study, photosynthetic responses induced by cadmium stress in chlorophyll biosynthesis, photochemical activities, the stability of thylakoid membranes chlorophyll-protein complexes and the chloroplast ultrastructure of the cereal crop Oryza sativa L. were characterized. Cadmium inhibited the biosynthesis of chlorophyll by interfering with activity of δ-aminolevulinic acid dehydratase in the rice seedlings. For the photochemical activities analyses, the extent of the decrease in photosystem II activity was much greater than that in the PS I activity. The variations in the chlorophyll a fluorescence parameters also indicated that cadmium toxicity drastically affected the photochemistry of PS II. Biochemical analyses by BN-PAGE and protein immunoblot showed that cadmium toxicity considerably affected the stability of PS II-core, cytb 6 /f, RuBisCO, PSI + LHCI and LHCII (Trimeric). We observed the rate of the thylakoid membranes protein degradation, was mainly at the level of RbcL, PsaA, Lhca1 and D1. In addition, the damages to chloroplast structure and thylakoid stacking analyzed by transmission electron microscopy were indicative of general disarray in the photosynthetic functions exerted by cadmium toxicity. These results are valuable for understanding the biological consequences of heavy metals contamination particularly in soils devoted to organic agriculture.

Iron-mediated [3 + 2] or [3 + 3] annulation of 2-(2-(ethynyl)phenoxy)-1-arylethanones: selective synthesis of indeno[1,2-c]chromenes and 5H-naphtho[1,2-c]chromenes.

An iron-mediated tandem annulation strategy has been developed for the synthesis of numerous functional indeno[1,2-c]chromenes and 5H-naphtho[1,2-c]chromenes. This work is the first to disclose an iron-mediated method through sequential electrophilic addition of a ketone to an alkyne and annulation tandem reaction. Importantly, a halide is introduced into the products by a ring-opening process among the annulation of alkynylcyclopropanes, which makes the methodology more attractive for organic synthesis.