Ammonium improved cell wall and cell membrane P reutilization and external P uptake in a putrescine and ethylene dependent pathway.

Ammonium promotes rice P uptake and reutilization better than nitrate, under P starvation conditions; however, the underlying mechanism remains unclear. In this study, ammonium treatment significantly increased putrescine and ethylene content in rice roots under P deficient conditions, by increasing the protein content of ornithine decarboxylase and 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase compared with nitrate treatment. Ammonium treatment increased rice root cell wall P release by increasing pectin content and pectin methyl esterase (PME) activity, increased rice shoot cell membrane P release by decreasing phosphorus-containing lipid components, and maintained internal P homeostasis by increasing OsPT2/6/8 expression compared with nitrate treatment. Ammonium also improved external P uptake by regulating root morphology and increased rice grain yield by increasing the panicle number compared with nitrate treatment. The application of putrescine and ethylene synthesis precursor ACC further improved the above process. Our results demonstrate for the first time that ammonium increases rice P acquisition, reutilization, and homeostasis, and rice grain yield, in a putrescine- and ethylene-dependent manner, better than nitrate, under P starvation conditions.

Unearthing the alleviatory mechanisms of hydrogen sulfide in aluminum toxicity in rice.

Hydrogen sulfide (H2S) improves aluminum (Al) resistance in rice, however, the underlying mechanism remains unclear. In the present study, treatment with 30-µM Al significantly inhibited rice root growth and increased the total Al content, apoplastic and cytoplasm Al concentration in the rice roots. However, pretreatment with NaHS (H2S donor) reversed these negative effects. Pretreatment with NaHS significantly increased energy production under Al toxicity conditions, such as by increasing the content of ATP and nonstructural carbohydrates. In addition, NaHS stimulated the AsA-GSH cycle to decrease the peroxidation damage induced by Al toxicity. Pretreatment with NaHS significantly inhibited ethylene emissions in the rice and then inhibited pectin synthesis and increased the pectin methylation degree to reduce cell wall Al deposition. The phytohormones indole-3-acetic and brassinolide were also involved in the alleviation of Al toxicity by H2S. The transcriptome results further confirmed that H2S alleviates Al toxicity by increasing the pathways relating to material and energy metabolism, redox reactions, cell wall components, and signal transduction. These findings improve our understanding of how H2S affects rice responses to Al toxicity, which will facilitate further studies on crop safety.

Putrescine alleviates aluminum toxicity in rice (Oryza sativa) by reducing cell wall Al contents in an ethylene-dependent manner.

Aluminum (Al3+ ) toxicity in acidic soils limits crop productivity worldwide. In this study, we found that putrescine (PUT) significantly alleviates Al toxicity in rice roots. The addition of 0.1 mM PUT promoted root elongation and reduced the Al content in the root apices of Nipponbare (Nip) and Kasalath (Kas) rice under Al toxicity conditions. Exogenous treatment with PUT reduced the cell wall Al content by reducing polysaccharide (pectin and hemicellulose) levels and pectin methylesterase (PME) activity in roots and decreased the translocation of Al from the external environment to the cytoplasm by downregulating the expression of OsNRAT1, which responsible to encode an Al transporter protein Nrat1 (Nramp aluminum transporter 1). The addition of PUT under Al toxicity conditions significantly inhibited ethylene emissions and suppressed the expression of genes involved in ethylene biosynthesis. Treatment with the ethylene precursor 1-aminocylopropane-1-carboxylic acid (ACC) significantly improved ethylene emission, inhibited root elongation, increased the Al accumulation in root tips and the root cell wall, and increased cell wall pectin and hemicellulose contents in both rice cultivars under Al toxicity conditions. The ethylene biosynthesis antagonist aminoethoxyvinylglycine (AVG, inhibitor of the ACC synthase) had the opposite effect and reduced PME activity. Together, our results show that PUT decreases the cell wall Al contents by suppressing ethylene emissions and decreases the symplastic Al levels by downregulating OsNRAT1 in rice.

Boron reduces cell wall aluminum content in rice (Oryza sativa) roots by decreasing H2O2 accumulation.

When boron (B) deficiency and aluminum (Al) toxicity co-exist in acidic soils, crop productivity is limited. In the current study, we found that 3 µM of B pretreatment significantly enhances rice root elongation under Al toxicity conditions. Pretreatment with B significantly decreases the deposition of Al in rice apoplasts, suppresses the synthesis of cell wall pectin, inhibits cell wall pectin methylesterase (PME) activity and its gene expression, and increases the expression of OsSTAR1 and OsSTAR2, which are responsible for reducing the Al content in the cell walls. In addition, B pretreatment significantly increases OsALS1 expression, thereby facilitating the transfer of Al from the cytoplasm to the vacuoles. However, B pretreatment had no effect on Al uptake and citric acid secretion. Pretreatment with B significantly increases the activity of ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), thus increasing the elimination rate of H2O2 in rice roots. Co-treatment using B and H2O2 does not increase root growth under Al toxicity conditions; it also improves pectin synthesis, enhances PME activity, and increases Al deposition in root cell walls. However, the co-treatment of B and H2O2 scavenger 4-hydroxy-TEMPO has an opposite effect. The above results indicate that applying B fertilizers in acidic soil can help decrease the side effects of Al toxicity on rice growth.

In2O 3 Nanotower Hydrogen Gas Sensors Based on Both Schottky Junction and Thermoelectronic Emission.

Indium oxide (In2O3) tower-shaped nanostructure gas sensors have been fabricated on Cr comb-shaped interdigitating electrodes with relatively narrower interspace of 1.5 µm using thermal evaporation of the mixed powders of In2O3 and active carbon. The Schottky contact between the In2O3 nanotower and the Cr comb-shaped interdigitating electrode forms the Cr/In2O3 nanotower Schottky diode, and the corresponding temperature-dependent I-V characteristics have been measured. The diode exhibits a low Schottky barrier height of 0.45 eV and ideality factor of 2.93 at room temperature. The In2O3 nanotower gas sensors have excellent gas-sensing characteristics to hydrogen concentration ranging from 2 to 1000 ppm at operating temperature of 120-275 °C, such as high response (83 % at 240 °C to 1000 ppm H2), good selectivity (response to H2, CH4, C2H2, and C3H8), and small deviation from the ideal value of power exponent ß (0.48578 at 240 °C). The sensors show fine long-term stability during exposure to 1000 ppm H2 under operating temperature of 240 °C in 30 days. Lots of oxygen vacancies and chemisorbed oxygen ions existing in the In2O3 nanotowers according to the x-ray photoelectron spectroscopy (XPS) results, the change of Schottky barrier height in the Cr/In2O3 Schottky junction, and the thermoelectronic emission due to the contact between two In2O3 nanotowers mainly contribute for the H2 sensing mechanism. The growth mechanism of the In2O3 nanotowers can be described to be the Vapor-Solid (VS) process.