不同浓度壳聚糖对炭黑曲霉和硫色镰刀菌生长和发育的影响

【背景】壳聚糖是广泛存在于甲壳动物的一种多糖,具有广谱的抗真菌活性,但壳聚糖是否影响炭黑曲霉(Aspergillus carbonarius)和硫色镰刀菌(Fusarium sulphureum)生长和发育尚未见报道。【目的】明确不同浓度壳聚糖对A. carbonarius和F. sulphureum生长和发育的影响。【方法】通过在PDA培养基中添加不同浓度壳聚糖,测定两种真菌的菌落直径、生物量和菌丝干重,观察产孢量、孢子萌发和芽管长度,比较抑菌的差异。【结果】壳聚糖处理可显著改变两种真菌的菌落形态,处理浓度越高菌落皱缩和变形越明显;壳聚糖还可以有效抑制两种真菌的菌落生长、菌丝干重和菌丝生物量,抑制效果呈明显的浓度依赖,对F. sulphureum的抑制效果更好。壳聚糖可抑制两种真菌的产孢量、孢子萌发和芽管伸长,处理浓度越高抑制效果越好,对F. sulphureum的抑制效果更为明显。壳聚糖对A. carbonarius和F. sulphureum的EC₅₀值分别为0.12 mg/mL和0.075 mg/mL。【结论】壳聚糖可有效抑制A. carbonarius和F. sulphureum的生长发育,抑制效果呈浓度依赖,F. sulphureum对壳聚糖更为敏感。     

PRECONDITIONING OF GERMINATION IN LETTUCE AT TIME OF FRUIT RIPENING

Koller , D. (The Hebrew U., Jerusalem. ² ) Preconditioning of germination in lettuce at time of fruit ripening. Amer. Jour. Bot. 49(8): 841–844. 1962.—The effects of controlled environments during maturation on subsequent germination response of the seed were investigated with the light-sensitive lettuce ‘Grand Rapids.‘ The plants matured under a variety of temperature/photoperiod combinations, after completing vegetative growth and flower initiation under identical conditions. Good seed set was obtained only at night temperatures between 17 and 23 C, under short-day (8-hr) conditions. Seed germination was tested at 20, 23 and 26 C, in continuous dark and after a light-break, respectively. The conditions under which the seed had ripened brought about quantitative changes in the germination response. The stimulating effects of a light-break on germination at high temperatures did not change, but maturation under high temperatures or in continuous light increased the high-temperature tolerance of seed germination both in continuous dark and after a short light-break.     

Equal diversity in disparate species assemblages: a comparison of native and exotic woodlands in California

The species richness of ecosystems can remain stable over time, despite changes in species composition and changes in the dominant plant species. While this pattern of stability is known to occur temporally, it has been examined poorly in a spatial context. To examine this spatially, the species richness, diversity and composition of native woodlands (of oak and bay trees) and exotic woodlands (of eucalypt trees) were compared in California. Species richness was nearly identical for understorey plants, leaf‐litter invertebrates, amphibians and birds; only rodents had significantly fewer species in eucalypt sites. Species diversity patterns (using the Shannon–Wiener Index) were qualitatively identical to those for species richness, except for leaf‐litter invertebrates, which were significantly more diverse in eucalypt sites during the spring. Species composition was different between sites, as evidenced by a principal components analysis, coefficients of similarity, and the relatively few species shared between native and eucalypt sites. Thus, the consistency in richness and diversity observed for most groups, in most seasons, occurred despite significant differences in species composition. These results are consistent with previous demonstrations of temporal stability, suggesting that species richness may often be stable, both temporally and spatially, despite changes in composition and regardless of the dominant vegetation.     

Insulin-induced translocation of IR to the nucleus in insulin responsive cells requires a nuclear translocation sequence

Insulin binding to its cell surface receptor (IR) activates a cascade of events leading to its biological effects. The Insulin-IR complex is rapidly internalized and then is either recycled back to the plasma membrane or sent to lysosomes for degradation. Although most of the receptor is recycled or degraded, a small amount may escape this pathway and migrate to the nucleus of the cell where it might be important in promulgation of receptor signals. In this study we explored the mechanism by which insulin induces IR translocation to the cell nucleus. Experiments were performed cultured L6 myoblasts, AML liver cells and 3T3-L1 adipocytes. Insulin treatment induced a rapid increase in nuclear IR protein levels within 2 to 5?min. Treatment with WGA, an inhibitor of nuclear import, reduced insulin-induced increases nuclear IR protein; IR was, however, translocated to a perinuclear location. Bioinformatics tools predicted a potential nuclear localization sequence (NLS) on IR. Immunofluorescence staining showed that a point mutation on the predicted NLS blocked insulin-induced IR nuclear translocation. In addition, blockade of nuclear IR activation in isolated nuclei by an IR blocking antibody abrogated insulin-induced increases in IR tyrosine phosphorylation and nuclear PKCδ levels. Furthermore, over expression of mutated IR reduced insulin-induced glucose uptake and PKB phosphorylation. When added to isolated nuclei, insulin induced IR phosphorylation but had no effect on nuclear IR protein levels. These results raise questions regarding the possible role of nuclear IR in IR signaling and insulin resistance.     

Sugar-regulated susceptibility of tomato fruit to Colletotrichum and Penicillium requires differential mechanisms of pathogenicity and fruit responses

Colletotrichum gloeosporioides and Penicillium expansum cause postharvest diseases in tropical and deciduous fruit. During colonization, C. gloeosporioides and P. expansum secrete ammonia in hosts with low sugar content (LowSC) and gluconic acid in hosts with high sugar content (HighSC), respectively, as a mechanism to modulate enhanced pathogenicity. We studied the pathogens interactions with tomato lines of similar genetic background but differing in their sugar content. Colletotrichum gloeosporioides showed enhanced colonization of the LowSC line with differential expression response of 15% of its genes including enhanced relative expression of glycosyl hydrolases, glucanase and MFS-transporter genes. Enhanced colonization of P. expansum occurred in the HighSC line, accompanied by an increase in carbohydrate metabolic processes mainly phosphoenolpyruvate carboxykinase, and only 4% of differentially expressed genes. Gene response of the two host lines strongly differed depending on the sugar level. Limited colonization of HighSC line by C. gloeosporioides was accompanied by a marked alteration of gene expression compared the LowSC response to the same pathogen; while colonization by P. expansum resulted in a similar response of the two different hosts. We suggest that this differential pattern of fungal/host responses may be the basis for the differential of host range of both pathogens in nature.     

High level expression in Escherichia coli of isopenicillin N synthase genes from Flavobacterium and Streptomyces, and recovery of active enzyme from inclusion bodies

A T7 promoter-based vector was used to express the isopenicillin N synthase (IPNS) genes of Flavobacterium sp. 12,154 and Streptomyces jumonjinensis in Escherichia coli. Most of the IPNS synthesized at 37 degrees C, and representing some 22% and 51% of the total cell protein respectively, occurred in an insoluble, enzymatically inactive form. Active IPNS was recovered in a rapid and simple two-step procedure in which the insoluble material was first denatured in 5 M urea and then refolded by passing the solubilized IPNS through a G-25 Sephadex sizing column. Further chromatography on DEAE-Sepharose resulted in highly active IPNS preparations. This procedure was found to be well suited for scaling up to produce large amounts of IPNS.