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Oxygen plays a crucial role in the synthesis of boron nitride (BN) and the preparation of BN ceramics. The effects of oxygen content on the microstructure and properties of BN fibers treated at 1600 °C have not been studied yet. In this work, polymer-derived BN fibers are cured at 300 °C under oxygen and pyrolyzed at 600 °C, 700 °C and 800 °C under ammonia as the pre-heated BN fibers. Then, these pre-heated BN fibers are treated at 1600 °C under nitrogen as the final BN fibers. The compositions and microstructures of the pre-heated and final BN fibers are investigated. As the pre-heated temperature increases, the oxygen contents of the pre-heated BN fibers decrease to 24 wt%, 17 wt% and 5 wt%, respectively. The structures of the pre-heated BN fibers transform from amorphous BN to turbostratic BN. The oxygen in the pre-heated BN fiber volatilizes as boron oxide during treatment at 1600 °C, promoting the formation and growth of h-BN in the final BN fiber, with the maximum grain size reaching 74 × 20 nm (La × Lc). As the grain size of the final BN fiber increases, the Young's modulus, density and oxidation resistance level of the BN fiber improve, and the dielectric properties decrease. The final BN fiber that underwent pre-heating at 700 °C has the best comprehensive properties, with a tensile strength of 1.11 GPa and a Young's modulus of 265 GPa. This study researches the relationship between composition, structure and performance, and provides a scientific basis for the preparation process of BN fibers. • The initial BN fibers with gradient oxygen content are obtained by controlling the nitridation temperature after air curing. • The higher the oxygen content in the initial BN fibers, the better the crystallinity of the BN fibers treating at 1600 °C. • The tensile strength of BN fiber with a grain size of 34 × 11 nm (La × Lc) is 1.11 GPa, and the Young's modulus is 265 GPa. [ABSTRACT FROM AUTHOR]

This study assessed the effects of seven combinations of maize (Zea mays) genes phosphoenolpyruvate carboxylase (pepc), pyruvate phosphate dikinase (ppdk), and NADP-malic enzyme (nadp-me), on the photosynthesis of Arabidopsis. The photosynthetic rate, carboxylation efficiency, and shoot-dry-weight of Zmpepc (PC), Zmpepc + Zmppdk (PCK), Zmpepc + Zmnadp-me (PCM), and Zmpepc + Zmppdk + Zmnadp-me (PCKM) were significantly higher than those of the control wild-type (WT), with a trends to be PCKM > PCK > PC and PCM > WT. This indicated that Zmpepc was a prerequisite for improved photosynthetic performance; Zmppdk had a positive effect on Zmpepc , and the triple gene combination had the most significant synergistic effects. PCKM significantly enhanced activity of photosystem (PS)II (K, J phase) and PSI, light energy absorption (ABS/CSm) and conversion (TRo/ABS), and electron transfer (ETo/TRo). PCKM up-regulated 18 photosynthesis-related proteins, among which, 11 were involved in light reaction resulting in improved light-energy absorption and conversion efficiency, electron transfer, activity and stability of PSII and PSI, and the ATP and NADPH production. The remaining seven proteins were involved in dark reaction. The up-regulation of these proteins in PCKM improved the coordinated operation of light and dark reaction, increasing the photosynthesis and dry weight ultimately. These results also provide a promising strategy for the genetic improvement of the photosynthetic performance of C 3 crops by inserting major C 4 photosynthetic genes. • Arabidopsis was transformed with C 4 plant genes (Zmpepc , Zmppdk and Zmnadp-me). • Joint expression of the three C 4 plant genes significantly enhanced photosynthesis. • Eighteen proteins involved in photosynthetic process were up-regulated. • The light-energy absorption, conversion and CO 2 assimilation were all improved. • The overproduction of the metabolites of C 4 process may work as signals. [ABSTRACT FROM AUTHOR]

Wheat is one of the staple food crops worldwide and breeding for high yield wheat is critical to meet the need of increasing world population. To determine the factors that limit wheat yield potential in Henan province, China, 30 wheat cultivars that have been widely grown in Henan province since 1940s were evaluated for grain yield and related physiological traits. The results show that grain yield has been significantly increased since 1940s, with an annual genetic gain of 1.09%, and the increased yield after 1900s was attributed to the introduction of 1BL/1RS translocation. The significant yield increase mainly resulted from a significant increase in grain number per spike (GNPS), thousand kernel weight (TKW) and harvest index (HI), and a significant decrease in plant height due to utilization of semi-dwarfing genes. The genetic improvement of assimilate accumulation and translocation was mainly reflected by the improvement in post-anthesis assimilate accumulation (PoAAA) and post-anthesis transportion rate (PoATR) of pre-anthesis assimilates (PrAA), with genetic gains of 0.63% and 1.89%, respectively. The improvement of the PoAAA was closely related to an increase in net photosynthetic rates ( P n ) of flag leaves at anthesis and 20 days after anthesis, and leaf area index (LAI) at 20 days after anthesis; whereas the improvement of the PoATR of the PrAA was closely associated with the improvement of accumulation and redistribution of the assimilates accumulated in stems and sheaths. As yield increased, the source-sink ratio significantly decreased, reflecting that the source has been gradually becoming a limiting factor to grain yield increase. Therefore, diverse strategies should be adopted to improve biomass (source) in future wheat breeding to meet the need of continuous increasing in wheat yield. [ABSTRACT FROM AUTHOR]