Rheum officinale Baill. is an important traditional Chinese medicinal herb, its dried roots and rhizomes being widely utilized to cure diverse diseases. However, previous studies mainly focused on the active compounds and their pharmacological effects, and the molecular mechanism underlying the biosynthesis of these ingredients in R. officinale is still elusive. Here, we performed comparative transcriptome analyses to elucidate the differentially expressed genes (DEGs) in the root, stem, and leaf of R. officinale. A total of 236,031 unigenes with N50 of 769 bp was generated, 136,329 (57.76%) of which were annotated. A total of 5884 DEGs was identified after the comparative analyses of different tissues; 175 and 126 key enzyme genes with tissue-specific expression were found in the anthraquinone, catechin/gallic acid biosynthetic pathway, respectively, and some of these key enzyme genes were verified by qRT-PCR. The phylogeny of the PKS III family in Polygonaceae indicated that probably only PL_741 PKSIII1, PL_11549 PKSIII5, and PL_101745 PKSIII6 encoded PKSIII in the polyketide pathway. These results will shed light on the molecular basis of the tissue-specific accumulation and regulation of secondary metabolites in R. officinale, and lay a foundation for the future genetic diversity, molecular assisted breeding, and germplasm resource improvement of this essential medicinal plant.
Polyester polyol (PP)-based polyurethanes (PUs) consisting of two difunctional acids [1,4-cyclohexanedicarboxylic acid (CHDA) and 1,6-adipic acid (AA)] and also two diols [1,4-cyclohexanedimethanol (CHDM) and 1,6-hexanediol (HDO)] were synthesized by a two-step procedure with a variable feed ratio of CHDA to AA but fixed ratio of CHDM and HDO. The prepared PPs and/or PUs were characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and atomic force microscopy. The effects of difunctional acids on the thermal, mechanical, and dynamic mechanical thermal properties of PPs or PU films were investigated by thermogravimetry analysis, differential thermogravimetry and dynamic mechanical thermal analysis. The results show that PP exhibits a lowest viscosity with the mole fraction of CHDA and AA at 3 : 7 whereas it delivers a lowest melting point with the mole fraction at 9 : 1. After PPs being cross-linked by isocyanate trimers, the impact resistance, shear strength and glass transition temperature increase the mixed-acid formulations with increasing the content of CHDA. In detail, the resultant PU almost simultaneously exhibits the best mechanical and thermal properties when the mole fraction of CHDA and AA is kept constant at 9 : 1, thus giving rise to a high glass transition temperature of 56.4 C and a onset decomposition temperature of 350 C, and also delivering a balanced toughness and hardness with an impact resistance of 100 J/g and storage modulus as high as 10 9 Pa. This path for synthesis of PP-based PU provides a design tool for high performance polymer coatings.
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