增强UV-B辐射对蚕豆叶片微粒体膜一些性质的影响

温室条件下,用0（Control）、8．65kJm－2d－1（TI）及11．2KJm－2d－1（t2）不同剂量的UV－B辐射处理蚕豆幼苗。Ca2 ．ATPase及Mg2 －ATPase的活性在辐射处理期间下降。在处理21d,T1和T2微粒体膜的MDA含量明显高于对照,同时IUFA急剧下降,且呈明显的剂量效应。14及21d时,膜磷脂的含量也明显下降。脂氧合酶（Lox）活性在第7及14天与对照相比都显著升高,而21d后迅速下降。结果表明,增强UV－B对微粒体膜的伤害可能是一方面导致正常酶合成与分解之间的平衡失调,另一方面导致了膜脂过氧化作用。     

Differential response of cycling and noncycling cells to inducers of DNA synthesis and mitosis

The objective of this study was to determine whether cells in G(0) phase are functionally distinct from those in G(1) with regard to their ability to respond to the inducers of DNA synthesis and to retard the cell cycle traverse of the G(2) component after fusion. Synchronized populations of HeLa cells in G(1) and human diploid fibroblasts in G(1) and G(0) phases were separately fused using UV-inactivated Sendai virus with HeLa cells prelabeled with [(3)H]ThdR and synchronized in S or G(2) phases. The kinetics of initiation of DNA synthesis in the nuclei of G(0) and G(1) cells residing in G(0)/S and G(1)/S dikaryons, respectively, were studied as a function of time after fusion. In the G(0)/G(2) and G(1)/G(2) fusions, the rate of entry into mitosis of the heterophasic binucleate cells was monitored in the presence of Colcemid. The effects of protein synthesis inhibition in the G(1) cells, and the UV irradiation of G(0) cells before fusion, on the rate of entry of the G(2) component into mitosis were also studied. The results of this study indicate that DNA synthesis can be induced in G(0)nuclei after fusion between G(0)- and S-phase cells, but G(0) nuclei are much slower than G(1) nuclei in responding to the inducers of DNA synthesis because the chromatin of G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells differ from G(1) cells with regard to their effects on the cell cycle progression of the G(2) nucleus into mitosis. This difference between G(0) and G(1) cells appears to depend on certain factors, probably nonhistone proteins, present in G(1) cells but absent in G(0) cells. These factors can be induced in G(0) cells by UV irradiation and inhibited in G(1) cells by cycloheximide treatment.     

Effect of oregano essential oil on microbiological and physico-chemical attributes of minced meat stored in air and modified atmospheres

AIMS: This study aimed to determine the combined effect of packaging (air, modified atmosphere) with or without the addition of essential oil not only on the selection of microbial association of meat but also to determine any significant difference in microbial metabolites produced from the prevailing bacteria. METHODS AND RESULTS: Samples of minced meat were mixed with different concentration of oregano essential oil (0, 0.05, 0.5 and 1% v/w) and packed under aerobic or with modified atmosphere (Mixed Gas Modified Atmosphere--MGMA, 40% CO2/30% N2/30% O2; or CO2 Modified Atmosphere--COMA, 100% CO2) and stored at 5 degrees C. In all packaging conditions, only concentrations of 0.5% and 1% oregano oil were effective. Inhibition was evident in the order air < MGMA < COMA. Oregano essential oil delayed glucose and lactate consumption aerobically as well as under MGMA. pH changes were also evident. Furthermore, proteolysis was significantly inhibited in aerobically stored samples, and so was the production of acetate under MAP. Similar results were obtained for the other organic acids eluted from HPLC column. CONCLUSIONS: Oregano essential oil delayed microbial growth and suppressed the final counts of the spoilage micro-organisms. It also caused a pronounced alteration in the physico-chemical properties of the minced meat. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbial analysis alone as spoilage index may misrepresent the effect of a hurdle such as essential oils on spoilage.     

Effect of NaCl and KCl on fate and growth/no growth interfaces of Listeria monocytogenes Scott A at different pH and nisin concentrations

AIMS: The fate of Listeria monocytogenes Scott A, was studied in broth, at different a(w)s (by adding NaCl or KCl from 0.0 to 1.4 mol l(-1)), pHs (from 4.0 to 7.3 by adding lactic acid), and nisin concentrations (from 0 to 100 IU ml(-1)). METHODS AND RESULTS: Increasing salt and nisin concentrations and decreasing pH resulted in lower growth rates and extended lag phases. At pH 4.5 no growth was observed while in presence of nisin and/or 1 mol l(-1) salts of both kinds, L. monocytogenes Scott A was inactivated. Equal-molar concentrations of NaCl or KCl (similar a(w)), exerted similar effects against L. monocytogenes in terms of lag phase duration, growth or death rate. The growth boundaries of L. monocytogenes Scott A at 5 degrees C were also estimated by growth/no growth turbidity data, modeled by logistic polynomial regression. The concordance of logistic models, were 99.6 and 99.8% for NaCl and KCl, respectively. CONCLUSIONS: The growth interfaces derived by both NaCl and KCl models were almost identical. Hence, NaCl can be replaced by KCl without risking the microbiological safety of the product. Increasing nisin concentrations markedly affected the interface resulting in a more inhibitory environment for L. monocytogenes Scott A. Low to medium salt concentrations (0.3-0.7 mol l(-1) of either NaCl or KCl) provided a protective effect against inhibition of L. monocytogenes Scott A by nisin. SIGNIFICANCE AND IMPACT OF THE STUDY: Modelling the growth boundaries not only contributes to the development of safer food by providing useful data, but can also be used to study interactions between factors affecting initiation of growth of pathogenic micro-organisms.     

Diaphragm adaptations in patients with COPD

Inspiratory muscle weakness in patients with COPD is of major clinical relevance. For instance, maximum inspiratory pressure generation is an independent determinant of survival in severe COPD. Traditionally, inspiratory muscle weakness has been ascribed to hyperinflation-induced diaphragm shortening. However, more recently, invasive evaluation of diaphragm contractile function, structure, and biochemistry demonstrated that cellular and molecular alterations occur, of which several can be considered pathologic of nature. Whereas the fiber type shift towards oxidative type I fibers in COPD diaphragm is regarded beneficial, rendering the overloaded diaphragm more resistant to fatigue, the reduction of diaphragm fiber force generation in vitro likely contributes to diaphragm weakness. The reduced diaphragm force generation at single fiber level is associated with loss of myosin content in these fibers. Moreover, the diaphragm in COPD is exposed to oxidative stress and sarcomeric injury. This review postulates that the oxidative stress and sarcomeric injury activate proteolytic machinery, leading to contractile protein wasting and, consequently, loss of force generating capacity of diaphragm fibers in patients with COPD. Interestingly, several of these presumed pathologic alterations are already present early in the course of the disease (GOLD I/II), although these patients appear not limited in their daily life activities. Treatment of diaphragm dysfunction in COPD is complex since its etiology is unclear, but recent findings indicate the ubiquitin-proteasome pathway as a prime target to attenuate diaphragm wasting in COPD.     

Comparison of the functions of glutathionylspermidine synthetase/amidase from E. coli and its predicted homologues YgiC and YjfC

Protein function prediction is very important in establishing the roles of various proteins in bacteria; however, some proteins in the E. coli genome have their function assigned based on low percent sequence homology that does not provide reliable assignments. We have made an attempt to verify the prediction that E. coli genes ygiC and yjfC encode proteins with the same function as glutathionylspermidine synthetase/amidase (GspSA). GspSA is a bifunctional enzyme that catalyzes the ATP-dependent formation and hydrolysis of glutathionylspermidine (G-Sp), a conjugate of glutathione (GSH) and spermidine. YgiC and YjfC proteins show 51% identity between themselves and 28% identity to the synthetase domain of the GspSA enzyme. YgiC and YjfC proteins were expressed and purified, and the properties of GspSA, YgiC, and YjfC were compared. In contrast to GspSA, proteins YgiC and YjfC did not bind to G-Sp immobilized on the affinity matrix. We demonstrated that all three proteins (GspSA, YgiC and YjfC) catalyze the hydrolysis of ATP; however, YgiC and YjfC cannot synthesize G-Sp, GSH, or GSH intermediates. gsp, ygiC, and yjfC genes were eliminated from the E. coli genome to test the ability of mutant strains to synthesize G-Sp conjugate. E. coli cells deficient in GspSA do not produce G-Sp while synthesis of the conjugate is not affected in ΔygiC and ΔyjfC mutants. All together our results indicate that YgiC and YjfC are not glutathionylspermidine synthetases as predicted from the amino acid sequence analysis.     

Comparison of growth limits of Listeria monocytogenes in milk,broth and cheese

Aim: To determine growth initiation differences of Listeria monocytogenes between a cheesemaking context, milk and tryptic soy broth (TSB). Methods and Results: A laboratory‐scale cheese was made with a mix of two strains of L. monocytogenes at four initial pH values, five water activity (a_w) values and two contamination levels at 30°C. Counts of L. monocytogenes were determined at time 0 and after 8 h of cheese manufacture. Milk and TSB at the same pH and a_w conditions were inoculated with the L. monocytogenes mix in multi‐well plates. Growth was determined by plating each well onto Agosti & Ottaviani Listeria Agar after 8 h of incubation at 30°C. Each condition was repeated six times, and growth initiation probability was modelled with logistic regression models. Growth initiation boundaries were obtained for each matrix type. The results showed that the growth limits were matrix dependent. In the three matrix types, a_w was the most important factor affecting the probability of growth initiation. Contamination level affected growth TSB and cheesemaking conditions. Conclusions: The interface wideness and position in cheese, milk and TSB were dissimilar, indicating that the use of models evaluated in TSB or milk could not be used to predict the behaviour of L. monocytogenes under cheesemaking conditions. Significance and Impact of the Study: Predictive models generated in liquid media are not necessarily adaptable to solid food, and the generation of real food models is necessary.     

Highly Invasive Listeria monocytogenes Strains Have Growth and Invasion Advantages in Strain Competition

Multiple Listeria monocytogenes strains can be present in the same food sample; moreover, infection with more than one L. monocytogenes strain can also occur. In this study we investigated the impact of strain competition on the growth and in vitro virulence potential of L. monocytogenes. We identified two strong competitor strains, whose growth was not (or only slightly) influenced by the presence of other strains and two weak competitor strains, which were outcompeted by other strains. Cell contact was essential for growth inhibition. In vitro virulence assays using human intestinal epithelial Caco2 cells showed a correlation between the invasion efficiency and growth inhibition: the strong growth competitor strains showed high invasiveness. Moreover, invasion efficiency of the highly invasive strain was further increased in certain combinations by the presence of a low invasive strain. In all tested combinations, the less invasive strain was outcompeted by the higher invasive strain. Studying the effect of cell contact on in vitro virulence competition revealed a complex pattern in which the observed effects depended only partially on cell-contact suggesting that competition occurs at two different levels: i) during co-cultivation prior to infection, which might influence the expression of virulence factors, and ii) during infection, when bacterial cells compete for the host cell. In conclusion, we show that growth of L. monocytogenes can be inhibited by strains of the same species leading potentially to biased recovery during enrichment procedures. Furthermore, the presence of more than one L. monocytogenes strain in food can lead to increased infection rates due to synergistic effects on the virulence potential.