Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5′-triphosphate

Addition of ATP to chloroplasts causes a reversible 25–30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at ?196°C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial (F_o) and variable (F_v) fluorescence such that the ratio of F_v to the maximum (F_m) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of F_v against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.     

Tolerance Limit of the Sugarbeet to Heterodera schachtii

Field and greenhouse experiments showed that yield losses of sugarbeet, Beta vulgaris, did not occur in soil infested with fewer than eight Heterodera schachtii eggs/g soil. However, larger population densities greatly reduced sugarbeet yield. In the field experiment, the yield in microplots inoculated with more than 64 eggs/g soil was less than 20% of yields in uninoculated microplots. Nevertheless, tolerance limits of 4 and 1.8 eggs/g soil, in greenhouse and field microplots, respectively, were derived by fitting the data with the equation y =m + (l - m)z^P-T. Maximum rates of multiplication of 55 and more than 300, and equilibrium densities of 340 and 130 eggs/g soil, were estimated in greenhouse and field microplot tests, respectively.     

A comparison of the inhibitory effects of melatonin and indomethacin on platelet aggregation and thromboxane release

Collagen-induced platelet aggregation and thromboxane release is inhibited, in a concentration response relationship, by preincubation of gel-filtered platelets with melatonin in the concentration range 430 nM – 4.3 mM. Inhibition of platelet aggregation and thromboxane release also occurs in the presence of indomethacin (4.3 nM – 4.3 mM), a known potent inhibitor of prostaglandin synthesis. Arachidonic acid-induced platelet aggregation and thromboxane release was inhibited in the presence of 4.0 mM melatonin. We therefore propose that inhibition of prostaglandin synthesis maybe the mechanism by which melatonin expresses its activity. Its antigonadotropic activity may result from inhibition of PGE₂ synthesis in the hypothalamus and median eminence.     

Mutant cell lines resistant to azetidine carboxylic acid: Quantitative and qualitative differences in pyrroline-5-carboxylate synthase activity

Mutant Chinese hamster lung fibroblasts were selected that are resistant to the proline analog L-azetidine-2-carboxylic acid. Resistance in the two mutant cell lines is associated with two distinct alterations in pyrroline-5-carboxylate synthase, the enzyme that catalyzes the proline biosynthetic step leading from glutamic acid to pyrroline-5-carboxylate. In one mutant cell line, pyrroline-5-carboxylate synthase specific activity is increased 30-fold over the level in control cells. In the other mutant line, pyrroline-5-carboxylate synthase activity is not increased, but the enzyme has become insensitive to inhibition by ornithine and proline.     

Effects of metabolic inhibitors on cell lethality and mutation induction in Chinese hamster cells. I. Inhibitors of de novo purine synthesis and a comparison with the effects of caffeine

The effect of pre- and posttreatment incubation of UV-irradiated and ethyl methanesulphonate (EMS) treated cells with non-toxic concentrations of inhibitors of de novo purine synthesis (dnPS) on expression of potentially lethal and premutational damage at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus in V79 cells has been examined. The concentrations of inhibitors used were shown to profoundly perturb de novo DNA synthesis, by measurements of [¹⁴C]formate uptake, and cell cycle progression by flow cytofluorimetry. Postincubation in 6-methyl mercaptopurine ribonucleoside (MMPR) usually but not invariably potentiated the cytotoxic effects of UV and EMS but azaserine (AZS) and methotrexate (MTX) were without effect. No effects on mutant frequencies were observed on posttreatment with any of these agents. Caffeine produced the least effect on dnPS, but invariably potentiated lethal damage. This potentiation of lethal damage is not mediated by dnPS inhibition as has been suggested for Chinese hamster ovary (CHO) cells.     

On the Estimation of the Population Mean with Known Coefficient of Variation

For the estimation of population mean a class of estimators has been proposed when the coefficient of variation is known and its efficiency is compared with the usual unbiased estimator and the estimators suggested by various researchers. The properties of the proposed class of estimators have been also discussed in the case of normal population.     

Effect of externally added carnitine on the synthesis of acetylcholine in rat cerebral cortex cells

Acetylcholine synthesis from radiolabelled glucose was monitored in cerebral cortex cells isolated from brains of suckling and adult rats. Acetylcholine synthesis was found much higher in suckling animals, both in the absence and presence of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) inhibitor, paraoxon. Together with choline (20 μM), carnitine was found to stimulate acetylcholine synthesis in a synergistic way in cortex cells from adult rats (18%). Choline, however, was incapable of reversing an inhibitory effect exerted by carnitine on acetylcholine synthesis in cortex cells from suckling animals. Distribution of carnitine derivatives was found significantly different in the cells from young and old animals, the content of acetylcarnitine decreased with age with a corresponding increase of free carnitine. The observed differences in carnitine effect on acetylcholine synthesis suggested that high acetylcarnitine in cells capable of β-oxidation might be correlated with the lower level of acetylcholine synthesis.     

乳源耐甲氧西林金黄色葡萄球菌icaA/D基因缺失株的构建及其生物被膜形成能力与耐药性分析

【背景】耐甲氧西林金黄色葡萄球菌(Methicillin Resistant Staphylococcus aureus,MRSA)是一种具有多重耐药性的人畜共患病原菌,常引起奶牛乳房炎等疾病。形成生物被膜是MRSA重要的耐药机制之一。研究发现ica操纵子调控的胞间多糖黏附素(Polysaccharide Intercellular Adhesin,PIA)通过促进MRSA的黏附与聚集介导生物被膜形成,icaA和icaD基因共表达可显著提高MRSA的N-乙酰葡聚糖转移酶活性,但icaA/D蛋白对MRSA生物被膜形成和耐药性的影响仍不清楚。【目的】探讨icaA/D基因、MRSA生物被膜形成及耐药性三者之间的相关性,为寻找药物作用新靶点提供科学依据。【方法】以具有多重耐药性且生物被膜形成能力强的乳源MRSA M5分离株为研究对象,利用同源重组技术构建其icaA/D基因缺失株;利用FITC-ConA染色结合激光共聚焦显微镜观察野生株与icaA/D基因缺失株的生物被膜形成过程与能力;采用微量肉汤稀释法测定14种抗菌药物对野生株与icaA/D基因缺失株的最小抑菌浓度(MinimumInhibitoryConcentration,MIC)。【结果】构建了MRSA M5的icaA/D基因缺失株。激光共聚焦显微镜下观察到野生株在培养16 h后形成了一层厚的成熟生物被膜,随后开始解离,直至120 h完全解离;而icaA/D基因缺失株在培养后16 h仅形成一薄层生物被膜,48h完全解离。10种受试抗菌药物对缺失株的MIC较野生株减小,而且缺失株对8种药物的敏感性由原来的耐药或中介转变为中介或敏感。【结论】icaA/D基因缺失可明显降低MRSA的生物被膜形成能力与耐药性。     

Sampling and distribution pattern of Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae) in citrus orchard

Developing efficient sampling protocols is essential to monitor crop pests. One vector of the citrus disease HLB, the African citrus psyllid Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae), currently threatens the lemon industry throughout the Mediterranean region. In this work, a pool of sampling methods devoted to monitoring the population of T. erytreae was compared, its spatial distribution in the orchard was assessed, and the minimum sampling effort for the best sampling method was estimated. Three lemon orchards in North-western Portugal were sampled for one year using two types of yellow sticky traps (standard yellow and fluorescent Saturn yellow), B-vac sampling and sweep net sampling. The method that best performed, in terms of cost-efficiency, was the yellow sticky traps. The two colours of the sticky traps tested did not yield a significantly different number of catches. The spatial distribution throughout the orchards was found to be aggregated towards the borders. A minimum of three sticky traps per hectare was found to be enough to estimate the population at 90% accuracy for the mean during the outbreak. These results should help to monitor and anticipate outbreaks that may even colonize neighbour orchards. Studies on the local dispersion patterns of T. erytreae throughout the orchard are mandatory to further refine and optimize efficient monitoring protocols.