Stimulation and inhibition of secretion by phorbol myristate acetate in different cell types

In washed human platelets and in HL60 granulocytes phorbol myristate acetate (PMA, 1-2000nM) synergised with threshold concentrations of secretogogues to induce a sustained maximum secretory response. Likewise, superoxide production from HL60 cells maintained a maximal response at PMA concentrations between 30-300nM. At concentrations up to 10nM PMA also augmented calcium ionophore, A23187, stimulated histamine release from rat peritoneal mast cells. However, in the mast cell PMA concentrations above 10nM reduced maximum histamine release in a dose-dependent manner.     

Proton translocation during denitrification in Rhodopseudomonas sphaeroides f. denitrificans

Proton translocation during the reduction of NO ₃ ^- , NO ₂ ^- , N₂O and O₂, with endogenous substrates, in washed cells of Rhodopseudomonas sphaeroides f. denitrificans was investigated by an oxidant pulse method. On adding NO ₂ ^- to washed cells, anaerobically in the dark, an alkalinization occurred in the reaction mixture followed by acidification. When NO ₃ ^- , N₂O or O₂ was added to cells in the dark or with these compounds and NO ₂ ^- in light an acidification only was observed. Proton translocation was inhibited by carbonyl cyanide-m-chlorophenyl hydrazone.Valinomycin treated cells produced acid in response to the addition of either NO ₃ ^- , NO ₂ ^- , N₂O or O₂. The proton extrusion stoichiometry ( ratios) in illuminated cells were as follows: NO ₃ ^- 0.5N₂, 4.82; NO ₂ ^- 0.5N₂, 5.43; N₂ON₂, 6.20; and O₂H₂O, 6.43. In the dark the comparable values were 3.99, 4.10, 4.17 and 3.95. Thus, illuminated cells produced higher values than those in the dark, indicating a close link between photosynthesis and denitrification in the generation of proton gradients across the bacterial cell membranes.When reduced benzyl viologen was the electron donor in the presence of 1 mM N-ethylmaleimide and 0.5 mM 2-n-heptyl-4-hydroxyquinoline-N-oxide in the dark, the addition of either NO ₃ ^- , NO ₂ ^- or N₂O to washed cells resulted in a rapid alkalinization of the reaction mixture. The stoichiometries for proton consumption, ratios without a permeant ion were NO ₃ ^- NO ₂ ^- ,-1.95; NO ₂ ^- 0.5 N₂O,-3.03 and N₂ON₂,-2.02. The data indicate that these reductions occur on the periplasmic side of the cytoplasmic membrane.Abbreviations BVH reduced benzyl viologen - CCCP carbonyl cyanide m-chlorophenyl hydrazone - DIECA N, N-diethyl-dithiocarbamate - HOQNO 2-n-heptyl-4-hydroxyquinoline-N-oxide - NEM N-ethylmaleimide     

Effects of newly synthesised platinum(ii) complexes on mitochondrial functions

Protease deficient recA431 mutants of Escherichia coli are defective in their capacity for induction of SOS responses and were intermediate in their sensitivities to ultraviolet light (UV) and cis-platinum(II)diamminodichloride (cis-PDD). Survival after treatment determined as colony forming ability was greater in rec⁺ strains and decreased in recA13 mutants which are defective in both recA proteolytic and recombination capabilites. In contrast, recA431 mutants were as sensitive to N-methyl-N′-nitro-N-nitrosoguanidine (NTG) as the recA13 cells. When cells carried either the pKM101 or N3 plasmid, survival after treatment with the three mutagens was increased. Presence of these plasmids in cells also resulted in hypermutagenicity as indicated by reversion of the argE3 mutation using a modified Ames test. Mutagenesis by NTG and cis-PDD was increased, as was survival of cells treated with UV light, cis-PDD and NTG in both recA⁺ and recA431 (protease deficient) strains. No plasmid mediated enhancement of mutagenesis or cell survival was observed in recA13 mutants. Thus, the ability of the plasmids to enhance cell survival and mutagenesis was dependent on recombination proficiency of the recA gene product and not its regulatory proteolytic activity. Unlike UV or NTG, presence of one of these plasmids was needed to detect reversion of the argE3 mutation by cis-PDD.     

Torsional motion of eosin-labeled F-actin as detected in the time-resolved anisotropy decay of the probe in the sub-millisecond time range

The internal motion of F-actin in the time range from 10(-6) to 10(-3) second has been explored by measuring the transient absorption anisotropy of eosin-labeled F-actin using laser flash photolysis. The transient absorption anisotropy of eosin-F-actin at 20 degrees C has a component that decays in the submicrosecond time scale to an anisotropy of about 0.3. This anisotropy then decays with a relaxation time of about 450 microseconds to a residual anisotropy of about 0.1 after 2 ms. When the concentration of eosin-F-actin was varied in the range from 7 to 28 microM, the transient absorption anisotropy curves obtained were almost indistinguishable from each other. These results show that the anisotropy decay arises from internal motion of eosin-F-actin. Analysis of the transient absorption anisotropy curves indicates that the internal motion detected by the decay in anisotropy is primarily a twisting of actin protomers in the F-actin helix; bending of the actin filament makes a minor contribution only to the measured decay. The torsional rigidity calculated from the transient absorption anisotropy is 0.2 X 10(-17) dyn cm2 at 20 degrees C, which is about an order of magnitude smaller than the flexural rigidity determined from previous studies. Thus, we conclude that F-actin is more flexible in twisting than in bending. The calculated root-mean-square fluctuation of the torsional angle between adjacent actin protomers in the actin helix is about 4 degrees at 20 degrees C. We also found that the torsional rigidity is approximately constant in the temperature range from 5 to approximately 35 degrees C, and that the binding of phalloidin does not appreciably affect the torsional motion of F-actin.     

Mechanism of proton-pumping in the cytochrome b/f complex

Several models have been proposed to interpret the mechanism of proton-pumping associated with the electron transfer reactions in the cytochrome b/f complex. Energetics considerations suggest that the proton pump is coupled to the oxidation of cytochrome b by plastoquinone. Experiments performed in living cells under anaerobic conditions suggest that proton-pumping can occur through two independent mechanisms. When the two b cytochromes are reduced prior to a flash illumination i.e. after a long dark anaerobic incubation (>10 minutes), proton-pumping is very likely associated with the reduction of a semiquinone by cyt b which occurs at a site close to the inner face of the membrane. The electrogenic phase is associated with the tranfer of protons via a transmembrane channel. This process is not inhibited by 2-n-nonyl-4-hydroxyquinoline N-oxide (NQNO). Under repetitive-flash or under aerobic conditions, proton-pumping occurs according to a modified Q-cycle mechanism, which is inhibited by NQNO.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement     

受白粉菌诱导大麦抗感等基因系蛋白质变化的双向电泳分析

分别对接种与否的大麦抗—感白粉病等基因系—叶期幼苗取材进行蛋白质双向电泳分析。结果表明,病原的侵入使抗—感两系在30Kd以下的低分子量区域的蛋白质发生了明显变化。接种48小时之后,抗病系在pH5.5、6.0、6.8及8.8附近出现了对照中所没有的蛋白质,而在pH6.0和8.8附近的蛋白质则较对照有减小的趋势;感病系在pH6.0附近蛋白质明显增多,在pH8.8处不仅在量上有大幅度提高,而且种类也有增加。结果还表明,抗—感系间在未接种的情况下双向电泳图谱也有差异,接种之后由于感病系在pH8.8处蛋白质的特异性合成,使抗—感两系间的差异缩小。     

中国茶藨子属(虎耳草科)新植物

<正> 灌木,高约2米。小枝微弯曲,黑褐色,无毛。冬芽长卵圆形。叶片呈不等的五角形,长7—13匣米,宽8—16厘米,先端长渐尖,基部深心形,边缘有不等重锯齿,上面深绿色,散生硬毛,下面淡绿色,沿脉被短柔毛,主脉和侧脉均突起;叶柄长5—9.5厘米,近无毛。总状花序,下垂,花梗长3—4毫米,和总花梗均被短柔毛,常混生星状毛。果实长圆形,红色,直径约6毫米;萼片宿存,反折,近无毛。     

Genetic variation in soybean photosynthetic electron transport capacity is related to plastocyanin concentration in the chloroplast

Fifteen ancestral genotypes of United States soybean cultivars were screened for differences in photosynthetic electron transport capacity using isolated thylakoid membranes. Plants were grown in controlled environment chambers under high or low irradiance conditions. Thylakoid membranes were isolated from mature leaves. Photosynthetic electron transport was assayed as uncoupled Hill activity using 2,6-dichlorophenolindophenol (DCIP). Soybean electron transport activity was dependent on genotype and growth irradiance and ranged from 6 to 91 mmol DCIP reduced [mol chlorophyll]^–1 s^–1. Soybean plastocyanin pool size ranged from 0.1 to 1.3 mol plastocyanin [mol Photosystem I]^–1. In contrast, barley and spinach electron transport activities were 140 and 170 mmol DCIP reduced [mol chlorophyll]^–1 s^–1, respectively, with plastocyanin pool sizes of 3 to 4 mol plastocyanin [mol Photosystem I]^–1. No significant differences in the concentrations of Photosystem II, plastoquinone, cytochrome b₆f complexes, or Photosystem I were observed. Thus, genetic differences in electron transport activity were correlated with plastocyanin pool size. The results suggested that plastocyanin pool size can vary significantly and may limit photosynthetic electron transport capacity in certain species such as soybean. Soybean plastocyanin consisted of two isoforms with apparent molecular masses of 14 and 11 kDa, whereas barley and spinach plastocyanins each consisted of single polypeptides of 8 and 12 kDa, respectively.Abbreviations DAP days after planting - DCIP 2,6-dichlorophenolindophenol - LiDS lithium dodecyl sulfate - PPFD photosynthetic photon flux density (mol photons m^–2 s^–1) - PS I Photosystem I - PS II Photosystem II - P700 reaction center of Photosystem I The US Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

The effect of reduced phytoalexin production on the resistance of upland cotton (Gossypium hirsutum) to verticillium and fusarium wilts

The effect on disease development of inhibiting the production of the sesquiterpenoid phytoalexin hemigossypol (HG) in cotton resistant to both verticillium and fusarium wilts was investigated. Inhibition was achieved by treating the plants with the sodium salt of compactin, a competitive inhibitor of hydroxy-methylglutaryl (HMG) CoA reductase. Compactin treatment (150 μg litre^-1) reduced HG production by a mean of 48%. The enzyme inhibitor did not mimic symptoms in uninfected plants or significantly reduce the ability of the conidia of either Fusarium oxysporum f.sp. vasinfectum or Verticillium dahliae to germinate. Treatment of infected plants with compactin resulted in a breakdown of resistance to verticillium wilt but not to fusarium wilt. These results support the view that HG production is the primary mechanism of resistance to verticillium wilt, but not to fusarium wilt.     

Behavioral responses of three species of ground beetle (Coleoptera: Carabidae) to olfactory cues associated with prey and habitat

The responses ofPterostichus melanarius Illiger,Harpalus rufipes DeGeer, andNebria brevicollis Fabricius (Coleoptera: Carabidae) to olfactory cues of prey and habitat were studied in a four-arm continuous-airflow olfactometer. The process was semiautomated using time-lapse image analysis by microcomputer. The primary constituent of the aphid alarm pheromone, (E)--farnesene (EBF), was synthesized and tested for a kairomonal role in prey detection by carabids. In addition, individual beetles were exposed to odors from live aphids, live collembolans, and a crude extract of wheat. All three beetle species showed evidence of olfaction.P. melanarius responded to all the odors except collembolans,H. rufipes responded to EBF and wheat, andN. brevicollis to collembolans. The use of a defence allomone as a prey-finding kairomone by certain carabid species has implications for pest management. Manipulation of predator chemical ecology by the inclusion of behavior-modifying compounds in a crop spray mix with reduced amounts of insecticide may allow for efficient aphid control with less environmental contamination.