橡胶草90年来主要研究成果及最新研究进展

天然橡胶是重要的国防战略物质,巴西橡胶树（Hevea brasiliensis（Willd.ex A.Juss.） Muell.Arg）是天然橡胶的唯一来源,天然橡胶商业化形式极为单一,潜在的供给不足问题亟待解决。因此,寻找可替代巴西橡胶树的产胶植物一直受到全世界高度重视。蒲公英属橡胶草（Taraxacum kok-saghyz Rodin）根部含有与橡胶树橡胶类似的天然橡胶分子,该植物主要分布在温带和寒带地区,具有易于机械化收获、生长周期短、遗传转化相对容易等特点,是最具开发潜力的产胶植物。本文对橡胶草90年（1931-2018）来的研究历史和主要成果进行了概括,对近10年取得的最新成果进行了深度分析,并预测橡胶草在未来天然橡胶产业中的作用,期望为开展橡胶草商业化生产和橡胶生物合成相关基础研究提供一定的参考。     

Water status of callus from Hevea brasiliensis during induction of somatic embryogenesis

To improve somatic embryogenesis in Hevea brasiliensis , the water and plant growth regulator status of the culture medium was studied. Induction of embryogenic tissue from the internal integument of immature seeds was clearly favored by stabilizing the water potential of the culture medium at –0.7 MPa, by using low and decreasing concentrations of 3,4-dichlorophenoxyacetic acid and benzyladenine or by incorporating 10^-7 M abscisic acid in the medium. Each of these changes in the medium favored a specific water status in the callus, namely a high relative water content (93 to 95%) and an elevated water potential (–0.9 MPa). These characteristics were apparently important for initiating somatic embryogenesis, and their decrease corresponded to the loss of embryogenic potential in the callus. Thus, the relative water content and water potential of callus appear to be good markers of its embryogenic state.     

Seasonal Changes of Cambial Activity and Phloem Development in Hevea brasiliensis

There is definitely seasonal activity in cambial growth in the trunk of Hevea brasi- liensis planted on Hainan Island and the cambial growth ceases during leaf-fail and leaf-absent period simultaneously with lower temperature and dries. The sieve elements founction for one-half year to two years. The variation in conducting-phloem thicknesses in a year is not significant and the conducting-phloem retains in about the same thickness during leaf-fall and leaf-absent period as that during the other periods in a year.     

农杆菌介导法在橡胶树遗传转化中的应用与展望

综述农杆菌介导法在巴西橡胶树遗传转化中的应用进展,分析影响农杆菌转化的关键因素,如植物基因型与外植体、菌株与载体类型、菌液浓度与侵染时间、vir诱导物、筛选剂与抑菌剂、培养基的组成和附加成分等,并对提高巴西橡胶树转化效率的策略进行探讨。     

Chitinase from Paracoccidioides brasiliensis: molecular cloning, structural, phylogenetic, expression and activity analysis

A full-length cDNA encoding a chitinase (Pbcts1) was cloned by screening a cDNA library from the yeast cells of Paracoccidioides brasiliensis. The cDNA consists of 1888 bp and encodes an ORF of 1218 bp corresponding to a protein of 45 kDa with 406 amino acid residues. The deduced PbCTS1 is composed of two signature family 18 catalytic domains and seems to belong to fungal/bacterial class. Phylogenetic analysis of PbCTS1 and other chitinases suggests the existence of paralogs of several chitinases to be grouped based on specialized functions, which may reflect the multiple and diverse roles played by fungi chitinases. Glycosyl hydrolase activity assays demonstrated that P. brasiliensis is able to produce and secrete these enzymes mainly during transition from yeast to mycelium. The fungus should be able to use chitin as a carbon source. The presence of an endocytic signal in the deduced protein suggests that it could be secreted by a vesicular nonclassical export pathway. The Pbcts1 expression in mycelium, yeast, during differentiation from mycelium to yeast and in yeast cells obtained from infected mice suggests the relevance of this molecule in P. brasiliensis electing PbCTS1 as an attractive drug target.     

Antimicrobial susceptibilities of strains of Nocardia brasiliensis isolated from soil of Tucumán

The activity of antimicrobial agents against soil isolates of N. brasiliensis was studied by determination of the minimum inhibitory concentrations (MICs) and disk diffusion technique, according to the National Committee for Clinical Laboratory Standards (NCCLS). The objectives were: (a) to study the patterns of sensitivity among regional strains of N. brasiliensis isolated from natural sources (soil) of different zones of Tucumán province; (b) to correlate these results with those previously obtained with regional strains of N. brasiliensis isolated from human mycetomas, as a contribution in the evaluation of the importance of the natural reservoir area of the potentially pathogen strains. The results obtained by both methods identified strains of N. brasiliensis from soils with similar patterns of susceptibility to the strains N. brasiliensis isolated from human mycetomas. This showed strains sensitive and resistant to antibiotics. The majority of the isolates of N. brasiliensis from soils showed higher susceptibilities to antibiotics than the strains isolated from human mycetomas. Among the antibiotics studied, cefotaxime, ceftriaxone and gentamicin were the most effective against all the regional strains tested, and these results are correlated with those obtained with regional strains that cause human mycetomas. This revised version was published online in June 2006 with corrections to the Cover Date.     

Presence of carnitine acetyltransferase in peroxisomes and in mitochondria of oleic acid-grown Saccharomyces cerevisiae

Abstract Paracoccidiodes brasiliensis , the agent of paracoccidioidomycosis, when grown in a synthetic medium, expresses at the cell surface of both yeast and mycelial forms acidic glycoconjugates containing N -acetlyneuraminic acid units. Sialic acids were extracted using mild hydrolytic conditions, and were identified by thin-layer and gas chromatography, standard colorimetry, reaction with periodate-resorcinol and mass spectrometry. Their surface location was inferred from fluorescent-lectin ( Limulus polyphemus agglutinin) binding to whole cells abrogated by previous treatment with neuraminidase. Expression of sialic acids on virulent yeast forms of P. brasiliensis (3.7 × 10⁶ residues per cell) may inhibit fungal phagocytosis during early infection, when the immunological response is still being built up.     

Clinical isolates of <Emphasis Type="Italic">Nocardia brasiliensis</Emphasis> from Japan exhibit variable susceptibility to the antibiotic imipenem

Clinical isolates of Nocardia brasiliensis from Japan were classified into two groups based on their susceptibility to the carbapenem antibiotic, imipenem (IPM). Of 33 strains tested, 10 belonged to an IPM susceptible group, with MIC of from 0.25 to 2 εg/ml and a MIC₈₀ value of 1.5 εg/ml for this antibiotic. The remaining 23 strains belonged to an IPMresistant group with MIC and MIC₈₀ values of 8–16 εg/ml and >16 εg/ml, respectively. The type strain of N. brasiliensis belonged to this resistant group. Analysis of 16S rDNA genes sequences showed that the IPM susceptible group had characteristic single nucleotide substitutions at positions 103 (T), 381 (A), and 456 (A), in contrast to the IPM resistant group. This grouping, however, was not associated with their clinical manifestation.