[Research advances in critical transition and its ecological mechanisms of terrestrial ecosystems.] / é™†åœ°ç”Ÿæ€ç³»ç»Ÿä¸´ç•Œè½¬æ¢ç†è®ºåŠå ¶ç”Ÿæ€å­¦æœºåˆ¶ç ”ç©¶è¿›å±•.

With the exacerbating disturbances of climate changes and human activities to terrestrial ecosystems, more and more studies realize that ecosystems are at the risk of shifts without warning in structural and functional states and recovery from perturbations require more time. Developing an early warning model to identify critical transition and understanding its ecological mechanism of typical ecosystems have become hotspot in ecological researches. At present, based on theoretical and experimental researches across multiple spatiotemporal scales, a variety of theoretical frameworks and indicators of early warning signals (EWSs) were proposed to signal terrestrial ecosystem critical transition. Here, in order to more thoroughly understand and construct theoretical frameworks and indicators of early warning signals, we reviewed advances in critical transitions from aspects of theoretical methods and processing mechanisms. Catastrophe theory and critical slowing down (CSD) are the two basic theories for early-warning ecosystem state transitions. Self-organization and feedback mechanisms are the primary ecological mechanisms to shape alternative stable state. Understanding cascade effects networks (CENet) among biological and environmental elements, and clarifying the equilibrium relationships between input and output of key ecosystem parameters are theoretical foundation of critical transition model. These theoretical cognitions could provide useful references to early warning of ecosystem disasters, ecological environment management and restoration.

Isolation of Flavonoids From Wild Aquilaria sinensis Leaves by an Improved Preparative High-Speed Counter-Current Chromatography Apparatus.

Four flavonoids including apigenin-7,4'-dimethylether, genkwanin, quercetin, and kaempferol were isolated in a preparative or semi-preparative scale from the leaves of wild Aquilaria sinensis using an improved preparative high-speed counter-current chromatography apparatus. The separations were performed with a two-phase solvent system composed of hexane-ethyl acetate, methanol-water at suitable volume ratios. The obtained fractions were analyzed by HPLC, and the identification of each target compound was carried out by ESI-MS and NMR. The yields of the above four target flavonoids were 4.7, 10.0, 11.0 and 4.4%, respectively. All these four flavonoids exhibited nitrite scavenging activities with the clearance rate of 12.40 ± 0.20%, 5.84 ± 0.03%, 28.10 ± 0.17% and 5.19 ± 0.11%, respectively. Quercetin was originally isolated from the Thymelaeaceae family, while kaempferol was isolated from the Aquilaria genus for the first time. In cytotoxicity test these two flavonoids exhibited moderate inhibitory activities against HepG2 cells with the IC50 values of 12.54 ± 1.37 and 38.63 ± 4.05 µM, respectively.

[Study on Triterpenoids from Helicteres angustifolia by High-Speed Countercurrent Chromatography].

Objective: To develop a method for separation and purification of triterpenoids from Helicteres angustifolia by highspeed countercurrent chromatography( HSCCC). Methods: The ethyl acetate extract of Helicteres angustifolia were separated by two-step HSCCC. The structures of the target compounds were identified by ESI-MS and1H-NMR and characterized by FTIR. Results: Six compounds were isolated and prepared from ethyl acetate extract of Helicteres angustifolia,and identified as methyl helicterilate( 1),methyl helicterate( 2),helicterilic acid( 3),helicteric acid( 4),betulic acid( 5),oleanolic acid( 6). The purity of the chemical constituents were determined by HPLC,and the mass fraction was more than 95. 0%,respectively. Conclusion: This method is suitable for the separation and preparation of triterpenoids from Helicteres angustifolia,which is rapid,high purity and high yield.

The genetic basis of white tigers.

The white tiger, an elusive Bengal tiger (Panthera tigris tigris) variant with white fur and dark stripes, has fascinated humans for centuries ever since its discovery in the jungles of India. Many white tigers in captivity are inbred in order to maintain this autosomal recessive trait and consequently suffer some health problems, leading to the controversial speculation that the white tiger mutation is perhaps a genetic defect. However, the genetic basis of this phenotype remains unknown. Here, we conducted genome-wide association mapping with restriction-site-associated DNA sequencing (RAD-seq) in a pedigree of 16 captive tigers segregating at the putative white locus, followed by whole-genome sequencing (WGS) of the three parents. Validation in 130 unrelated tigers identified the causative mutation to be an amino acid change (A477V) in the transporter protein SLC45A2. Three-dimensional homology modeling suggests that the substitution may partially block the transporter channel cavity and thus affect melanogenesis. We demonstrate the feasibility of combining RAD-seq and WGS to rapidly map exotic variants in nonmodel organisms. Our results identify the basis of the longstanding white tiger mystery as the same gene underlying color variation in human, horse, and chicken and highlight its significance as part of the species' natural polymorphism that is viable in the wild.

[Separation of eleutheroside E from crude extract of Radix Acanthopanacis Senticosus by analytical and preparative high-speed countercurrent chromatography].

Analytical high-speed countercurrent chromatography (HSCCC) was used for the systematic optimization of the two-phase solvent system to separate eleutheroside E from crude extract of Radix Acanthopanacis Senticosus. Eleutheroside E was obtained by preparative HSCCC with two-phase solvent system composed of chloroform-methanol-isopropanol-water (5:6:1:4 in volume ratio). The mobile phase is the lower phase and operated at a flow-rate of 2.0 mL/min, while the apparatus rotated at 800 r/min. High performance liquid chromatographic analysis of eleutheroside E revealed that its purity was over 98%. HSCCC is a useful method for the separation of natural products.