Olfactory discrimination of complex mixtures of amino acids by the black bullhead Ameiurus melas

On the basis of previous findings of behavioural discrimination of amino acids and on the knowledge of electrophysiology of the catfish (genera Ictalurus and Ameiurus) olfactory organs, behavioural experiments that investigated olfactory discrimination of amino acid mixtures were carried out on the black bullhead Ameiurus melas. Repeated presentations of food‐rewarded mixtures released increased swimming activity measured by counting the number of turns >90° within 90 s of stimulus addition. Non‐rewarded amino acids and their mixtures released little swimming activity, indicating that A. melas discriminated between the conditioned and the non‐conditioned stimuli. Two questions of mixture discrimination were addressed: (1) Are A. melas able to detect components within simple and complex amino acid mixtures? (2) What are the smallest differences between two complex mixtures that A. melas can detect? Three and 13 component mixtures tested were composed primarily of equipotent amino acids [determined by equal electroolfactogram (EOG) amplitude] that contained L‐Cys at ×100 the equipotent concentration. Ameiurus melas initially perceived the ternary amino acid mixture as its more stimulatory component alone [i.e. cysteine (Cys)], whereas the conditioned 13 component mixture containing the more stimulatory L‐Cys was perceived immediately as different from L‐Cys alone. The results indicate that components of ternary mixtures are detectable by A. melas but not those of more complex mixtures. To test for the smallest detectable differences in composition between similar multimixtures, all mixture components were equipotent. Initially, A. melas were unable to discriminate the mixtures of six amino acids from the conditioned mixtures of seven amino acids, whereas they discriminated immediately the mixtures of four and five amino acids from the conditioned mixture. Experience with dissimilar mixtures enabled the A. melas to start discriminating the seven‐component conditioned mixture from its six‐component counterparts. After fewer than five training trials, A. melas discriminated the mixtures of nine and 10 amino acids from a conditioned mixture of 12 equipotent amino acids; however, irrespective of the number of training trials, A. melas were unable to discriminate the 12 component mixture from its 11 component counterparts.     

Mixtures of plant growth-promoting rhizobacteria for induction of systemic resistance against multiple plant diseases

Studies of induced systemic resistance using strains of plant growth-promoting rhizobacteria (PGPR) have concentrated on the use of individual PGPR as inducers against multiple diseases of a single crop. To date, few reports have examined the potential of PGPR strain mixtures to induce systemic resistance against diseases of several different plant hosts. The objective of this study was to select mixtures of compatible PGPR strains with the capacity to elicit induced systemic resistance in four hosts. The specific diseases and hosts tested in this study included: bacterial wilt of tomato (Lycopersicon esculentum) caused by Ralstonia solanacearum, anthracnose of long cayenne pepper (Capsicum annuum var. acuminatum) caused by Colletotrichum gloeosporioides, damping off of green kuang futsoi (Brassica chinensis var. parachinensis) caused by Rhizoctonia solani, and cucumber mosaic virus (CMV) on cucumber (Cucumis sativus). To examine compatibility, seven selected PGPR strains were individually tested for in vitro antibiosis against all other PGPR strains and against three of the tested pathogens (R. solanacearum, C. gloeosporioides, and R. solani). No in vitro antibiosis was observed among PGPR strains or against pathogens. Twenty-one combinations of PGPR and seven individual PGPR were tested in the greenhouse for induced resistance activity. Results indicated that four mixtures of PGPR and one individual strain treatment significantly reduced the severity of all four diseases compared to the nonbacterized control: 11 mixtures reduced CMV of cucumber, 16 mixtures reduced bacterial wilt of tomato, 18 mixtures reduced anthracnose of long cayenne pepper, and 7 mixtures reduced damping off of green kuang futsoi. Most mixtures of PGPR provided a greater disease suppression than individual PGPR strains. These results suggest that mixtures of PGPR can elicit induced systemic resistance to fungal, bacterial, and viral diseases in the four hosts tested.     

The utilization of the mixtures of monosaccharides by some mucorales

Summary The utilization of mixtures of monosaccharides byBlakeslea trispora Thaxter,Choanephora circinans (Naganish &Kawakami)Hesseltine &Benjamin,Gilbertella persicaria var.indica Mehrotra &Mehrotra andHelicostylum piriforme Bainier was studied. The effect of sorbose on the utilization of other sugars present in the mixtures was also studied. It was found that all the mixtures of sugars in combination with asparagine or ammonium chloride were valueless for all the organisms exceptHelicostylum piriforme. Growth ofHelicostylum piriforme on the mixtures with asparagine as the nitrogen source was better than on the mixtures with ammonium chloride as the source of nitrogen. Asparagine being a favourable source counteractecd sorbose inhibition, while ammonium chloride failed to do so. On the other hand, both of the nitrogen sources failed to counteract sorbose inhibition in the rest of the organisms. None of the organisms could finish sorbose and rhamnose from any of the mixtures within the specified period.     

Interspecific interactions under fertilization among Elymus nutans,Festuca sinensis and Festuca ovina on the eastern Qinghai‐Tibetan plateau

A field replacement experiment was used to study the interspecific interaction among three perennial grasses (Elymus nutans, Festuca sinensis and Festuca ovina) that are distributed widely on the east Qinghai‐Tibetan plateau. The experiment consisted of four different species mixtures at four seeding densities and two fertilizer levels. Above‐ground biomass, relative yield and complementary effect were determined from harvested shoot dry weights. The results showed that above‐ground biomass was greater in all species mixtures than in monocultures. The difference between the observed and expected relative yield was greater than zero in all mixtures for E. nutans and was greater than zero in the F. sinensis/F. ovina mixture, but was below zero in all other mixtures for F. sinensis, and was below zero in all mixtures for F. ovina. The complementary effect was more negative across all seeding densities except at a seeding density of 400 seeds/m², and was negative across all mixtures except the F. sinensis/F. ovina mixture. In addition, fertilization had an insignificant impact on the relative yield, but a significant impact on the complementary effect. Fertilization enhanced negative interspecific interaction among the species.     

A quantitative review comparing the yield of switchgrass in monocultures and mixtures in relation to climate and management factors

Switchgrass (Panicum virgatum L.), a US Department of Energy model species, is widely considered for US biomass energy production. While previous studies have demonstrated the effect of climate and management factors on biomass yield and chemical characteristics of switchgrass monocultures, information is lacking on the yield of switchgrass grown in combination with other species for biomass energy. Therefore, the objective of this quantitative review is to compare the effect of climate and management factors on the yield of switchgrass monocultures, as well as on mixtures of switchgrass, and other species. We examined all peer‐reviewed articles describing productivity of switchgrass and extracted dry matter yields, stand age, nitrogen fertilization (N), temperature (growing degree days), and precipitation/irrigation. Switchgrass yield was greater when grown in monocultures (10.9 t ha^?1, n=324) than when grown in mixtures (4.4 t ha^?1, n=85); yield in monocultures was also greater than the total yield of all species in the mixtures (6.9 t ha^?1, n=90). The presence of legume species in mixtures increased switchgrass yield from 3.1 t ha^?1 (n=65) to 8.9 t ha^?1 (n=20). Total yield of switchgrass‐dominated mixtures with legumes reached 9.9 t ha^?1 (n=25), which was not significantly different from the monoculture yield. The results demonstrated the potential of switchgrass for use as a biomass energy crop in both monocultures and mixtures across a wide geographic range. Monocultures, but not mixtures, showed a significant positive response to N and precipitation. The response to N for monocultures was consistent for newly established (stand age <3 years) and mature stands (stand age ≥3 years) and for lowland and upland ecotypes. In conclusion, these results suggest that fertilization with N will increase yield in monocultures, but not mixtures. For monocultures, N treatment need not be changed based on ecotype and stand age; and for mixtures, legumes should be included as an alternative N source.     

Identification of a radical formed in the reaction mixtures of oxidized phosphatidylcholine with ferrous ions using HPLC–ESR and HPLC–ESR–MS

Identification of free radicals was performed for the reaction mixtures of autoxidized 1,2-dilinoleoylphosphatidylcholine (DLPC) with ferrous ions (or DLPC hydroperoxide with ferrous ions) and of DLPC with soybean lipoxygenase using electron spin resonance (ESR), high performance liquid chromatography (HPLC)–ESR and HPLC–ESR–mass spectrometry (MS) combined use of spin trapping technique. ESR measurements of the reaction mixtures showed prominent signals with hyperfine coupling constants (a^N=1.58?mT and a^Hβ=0.26?mT). Outstanding peaks with almost same retention times (autoxidized DLPC, 36.9?min; DLPC hydroperoxide, 35.0?min; DLPC with soybean lipoxygenase, 37.1?min) were observed on the elution profile of the HPLC–ESR analyses of the reaction mixtures. HPLC–ESR–MS analyses of the reaction mixtures gave two ions at m/z 266 and 179, suggesting that 4-POBN/pentyl radical adduct forms in these reaction mixtures.     

Physical properties of insect cuticular hydrocarbons: Model mixtures and lipid interactions

Cuticular lipids include a diverse array of hydrophobic molecules that play an important role in the water economy of terrestrial arthropods. Their waterproofing abilities are believed to depend largely on their physical properties, but little is known about interactions between different surface lipids to determine the phase behavior of the total lipid mixture. I examined the biophysical properties of binary hydrocarbon mixtures, as a model for interactions between different epicuticular lipids of insects. The midpoint of the solid/liquid phase transition (T_m) for mixtures of n-alkanes differing in chain length equaled the weighted average of the T_ms of the component lipids. This was also true for n-alkane-methylalkane mixtures. However, alkane-alkene mixtures melted at temperatures up to 17°C above the temperature predicted from the weighted average of component lipid T_m values. Hydrocarbon mixtures did not exhibit biphasic melting transitions indicative of independent phase behavior of the component lipids. Instead, melting occurred continuously, over a broader temperature range than pure hydrocarbons.     

A comparison between allozyme data and phenotypic distances from defensive secretion in Oreina leaf-beetles (Chrysomelinae)

The genetic relationships between five Oreina species (Chrysomelidae, Coleoptera) were studied. Of these species, four (O. bifrons, O. gloriosa, O. speciosa, O. variabilis) feed on Apiaceae and secrete mixtures of autogenous cardenolides from defensive glands, whilst the other (O. speciosissima) feeds on Asteraceae and is able both to produce cardenolides and to sequester pyrrolizidines N-oxides (PAs). A dendrogram based on the different mixtures of cardenolides produced by the different species agreed with these genetic relationships. In other words, cardenolide mixtures are good taxonomic markers, since the clustering method based on chemical defense produces a branching pattern similar to that based on genetic relationships.     

In vitro test systems supporting the development of improved pest control methods: a case study with chemical mixtures and bivalve biofoulers

Using the bivalve macrofouler Corbicula fluminea, the suitability of in vitro testing as a stepping stone towards the improvement of control methods based on chemical mixtures was addressed in this study. In vitro cholinesterase (ChE) activity inhibition following single exposure of C. fluminea tissue to four model chemicals (the organophosphates dimethoate and dichlorvos, copper and sodium dodecyl phosphate [SDS]) was first assessed. Consequently, mixtures of dimethoate with copper and dichlorvos with SDS were tested and modelled; mixtures with ChE revealed synergistic interactions for both chemical pairs. These synergic combinations were subsequently validated in vivo and the increased control potential of these selected combinations was verified, with gains of up to 50% in C. fluminea mortality relative to corresponding single chemical treatments. Such consistency supports the suitability of using time- and cost-effective surrogate testing platforms to assist the development of biofouling control strategies incorporating mixtures.     

Responses of olfactory receptor neurons in the spiny lobster to binary mixtures are predictable using a noncompetitive model that incorporates excitatory and inhibitory transduction pathways

Coding of binary mixtures by a population of olfactory receptor neurons in the spiny lobster (Panulirus argus) was examined. Extracellular single-unit responses of 50 neurons to seven compounds and their binary mixtures were recorded. The ability of a noncompetitive model with correction for binding inhibition to predict responses to mixtures based on responses to their components was compared with the predictive abilities of other models. This model assumes that different compounds activate different transduction processes in the same neuron leading to excitation or inhibition, and it includes a term quantifying the degree to which binding of an odorant to its receptor sites is inhibited by other compounds. The model accurately predicted the absolute response magnitude of the population of neurons for 13 of 15 mixtures assessed, which is superior to the predictive power of any of the other models. The model also accurately predicted the across neuron patterns generated by the binary mixtures, as evaluated by multidimensional scaling analysis. The results suggest that there is no emergence of unique qualities for binary mixtures relative to components of these mixtures.Abbreviations AMP or A adenosine-5-monophosphate - ANP across neuron pattern - ARM absolute response magnitude - ASW artificial sea water - Bet or B betaine - Cys or C L-cysteine - Glu or G L-glutamate - MDS multidimensional scaling - MID mixture interaction distance - NC model noncompetitive model - NCBI model noncompetitive model with correction for binding inhibition - C model competitive model - CBI model competitive model with correction for binding inhibition - MEC more effective component - NH ₄ or N ammonium chloride - ORN olfactory receptor neuron - Suc or S DL-succinate - Tau or T taurine     

THE ECOLOGY AND GENETICS OF FITNESS IN CHLAMYDOMONAS. IV. THE PROPERTIES OF MIXTURES OF GENOTYPES OF THE SAME SPECIES

The properties of mixtures of genotypes of Chlamydomonas reinhardtii were investigated by growing them in monoculture and in all possible pairwise combinations in chemically defined axenic medium. Two sets of genotypes produced by crossing wild-type isolates were cultured in each of two physical environments. Mixtures were consistently more productive and less variable over environments than were their constituent monocultures. The average performance of a genotype in mixture was tightly correlated with its performance in monoculture. Reisolation of spores from mixtures at the end of growth showed that the mixtures became dominated by the component with the greater performance in monoculture, so that the properties of mixtures were attributable to replacement rather than to complementation. These results differ from those of similar trials using a range of different species of Chlamydomonas, where genetic interactions were found to be important. They are discussed in relation to theories of diversity and diversification, and related to the agronomic use of crop mixtures.     

Competitive Aggressiveness in Binary Mixtures of Fusarium graminearum and F. culmorum Isolates Inoculated on Spring Wheat with Highly Effective Resistance QTL

Fusarium head blight (FHB) caused by Fusarium graminearum and F. culmorum is a devastating disease with high effects on grain yield and quality. We developed spring wheat lines incorporating the highly effective FHB resistance quantitative trait loci (QTL) Fhb1 and Qfhs.ifa‐5A. Whether these QTL lead to competition within Fusarium populations in the field resulting in isolates with higher aggressiveness has not been analysed. The aims of this study were to determine (i) the aggressiveness potential of F. graminearum and F. culmorum isolates, (ii) competition effects of these isolates in binary mixtures and (iii) the stability of resistant hosts. Six F. graminearum, two F. culmorum isolates and seven binary mixtures containing these isolates were tested for their aggressiveness and mycotoxin production at two locations in South Germany in 2007 and 2008. Host lines were four spring wheat lines containing the resistance QTL Fhb1 and/or Qfhs.ifa‐5A or none of them and one standard variety. Re‐isolates were sampled from plots inoculated with the binary mixtures to identify the percentage of each isolate in the mixture by simple sequence repeat markers. Resistant host lines reacted as expected and had a high stability to all isolates and mixtures. Only less important host × mixture interactions were detected. Aggressiveness among isolates and mixtures was significantly different. Type and amount of mycotoxin and high single isolate aggressiveness were not necessarily advantageous in the mixture. However, both F. culmorum isolates outcompeted F. graminearum isolates. Significant deviations from the inoculated 1 : 1 proportions occurred in 34 of 49 cases, illustrating that competition effects appeared in the mixtures. These differences depended mainly on the year and not on the level of host resistance. We conclude that resistance should not be affected by the Fusarium isolates and mixtures.     

Testing of different antibiotics against Gram-positive and Gram-negative bacteria isolated from plant tissue culture

Different Gram-positive and Gram-negative bacteria (Staphylococcus xylosus, S. aureus, S. cohnii, Bacillus sp., Corynebacterium sp., Pseudomonas vesicularis) were isolated from homogenized shoot tips of Drosera rotundifolia, Spatiphyllum sp., Syngonium cv. White butterfly, Nephrolepis exaltata cv. Teddy Junior. Growth inhibition of selected bacterial strains was examined using 28 different single antibiotics and 7 antibiotic mixtures. It was found that with the two mixtures Imipenem/Ampicillin and Imipenem/Penicillin G at concentrations of 5 mg l^–1 each, bacterial growth inhibition was most effective. Because of the lack of toxic effects on in vitro plants of 7 species it was proposed that these antibiotic mixtures can be applied advantageously to inhibit bacterial growth in tissue culture.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticksAmblyomma hebraeum andA. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO₂/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. InA. variegatum, aggregation was induced by methyl salicylate,o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed malesA. variegatum and a weak response was induced by an extract of 50 prefed males ofA. hebraeum. InA. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males ofA. hebraeum orA. variegatum and 50 live prefed males ofA. hebraeum. InA. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. InA. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.     

Competition between Australian native and introduced grasses along a nutrient gradient

Abstract Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16× the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia (Themeda triandra, Poa labillardieri and Danthonia carphoides); (ii) two introduced annuals (Vulpia bromoides and Hordeum leporinum); and (iii) two introduced perennials (Lolium perenne and Dactylis glomerata). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south‐eastern Australian grasslands after 150 years of continuous grazing by sheep.     

Uptake of cobalt and cesium by microalgal- and cyanobacterial-clay mixtures

Accumulation of cobalt and cesium by the microalga Scenedesmus obliquus and the cyanobacterium Synechocystis PCC 6803 has been characterized at metal concentrations ranging from 1–100 µM in the presence of three clay minerals, montmorillonite, illite, and kaolinite. The majority of metal uptake over a 4 h period consisted of rapid binding to the clay mineral-cell aggregates, and was unaffected by incubation in the dark or by the presence of the metabolic inhibitor carbonyl cyanide-3-chlorophenyl hydrazone (CCCP). This was followed by a slower, energy-dependent uptake of metal by the cell components of the mixtures, which was inhibited by incubation in the dark or in the presence of CCCP. The initial phase of uptake by the clay mineral-cell mixtures and mixture components alone conformed to a Freundlich adsorption isotherm, the order of uptake for both cobalt and cesium being montmorillonite-cells > illite-cells > kaolinite-cells. S. obliquus-clay mineral mixtures accumulated more cobalt and cesium than Synechocystis PCC 6803-clay mineral mixtures. On a dry weight basis, clay minerals alone accumulated greater amounts of metals than clay mineral-cell mixtures, which accumulated more than the cells alone. However, when the same data was expressed as amount of metal adsorbed per unit surface area, S. obliquus, in most cases, adsorbed greater amounts of cobalt and cesium than the clay minerals or Synechocystis PCC 6803. As the proportion of clay in a cell-clay mineral mixture was increased, the amount of metal accumulated also increased. Reduced accumulation of cobalt and cesium by cell-clay mineral mixtures, exhibited by equal amounts of the individual components added together, indicated that the formation of clay-cell aggregates had masked some of the binding sites normally available to metal ions. Accumulation of cobalt and cesium by all clay mineral-cell mixtures was dependent on the external pH and NaCl concentration, and decreased with decreasing pH and increasing external NaCl concentration. Offprint requests to: G. M. Gadd.     

Biotransformation of free fatty acids in mixtures to methyl ketones by Monascus purpureus

Summary Monascus purpureus converts short-chain fatty acids to methyl ketones. The regulation of the metabolic pathway is similar to that found in Penicillium roquefortii. There are differences in the actual amount of precursors metabolized. The fermentation of fatty acid mixtures led to methyl ketone mixtures. The metabolism of each fatty acid was dependent on the precursor composition. Offprint requests to: C. Kranz     

Studying effects of some surfactants and detergents on filter-feeding bivalves

Effects of several surfactants and chemical mixtures on marine bivalves were studied. An anionic surfactant, sodium dodecylsulphate (SDS), and a cationic surfactant, tetradecyltrimethylammonium bromide (TDTMA), inhibited the filtering activity of oysters (Crassostrea gigas). Similar effects were exhibited by some chemical mixtures that included surfactants. Those mixtures inhibited the filtering activity of Crassostrea gigas and Mytilus galloprovincialis. The new results are in agreement with the author's previous experiments, where a number of xenobiotics and/or pollutants inhibited the filtering activity of several species of marine and freshwater bivalves, e.g., it had been shown that SDS inhibited filtering activity of Mytilus edulis (e.g., Ostroumov, 2000c, 2001a). This experimental approach is helpful in assessment of environmental hazards from man-made chemicals that can contaminate marine systems.     

Effect of stereoconfiguration on ripple phases (Pβ′) of dipalmitoylphosphatidylcholine

Mixtures of sn-1 ( ) and sn-3 ( ) enantiomers of fully hydrated dipalmitoylphosphatidylcholine (DPPC) were studied with differential scanning calorimetry and freeze-fracture microscopy. The pretransition temperature of racemic mixtures of DPPC was 1.8 C° below that of either pure sn-1 or sn-3 enantiomers, which had similar pretransition temperatures. The main transition temperature of racemic mixtures was also depressed, but to a lesser extent, 0.8 C°. Freeze-fracture images of liposomes of sn-1, sn-3, and racemic mixtures of DPPC frozen from the P_β′ phase showed well-defined ripples of wavelength 13 nm. Lipid stereoconfiguration had no effect on ripple wavelength, configuration or amplitude, or on the number and nature of surface defects.     

Application of immunodiffusion to the identification of Rhizobium meliloti strains competing for nodulation on Medicago sativa

The immunodiffusion technique was successfully used to unambiguously recognize four strains of Rhizobium meliloti in a study of competition for nodulation with Medicago sativa cv. Apollo inoculated with two-, three- and fourstrain mixtures. The serological reactions of all R. meliloti strains revealed no significant changes following plant passage indicating that the antigens involved in immunodiffusion were stable. R. meliloti 102F70 formed 50% or more of the nodules on M. sativa inoculated with two-, three- and four-strain mixtures. The remaining three strains were less competitive and produced similar proportions of nodules (14–20%) on plants inoculated with three- and four-strain mixtures. Cases of mixed-strain occupancy of nodules involving either two of three strains were detected in a sub-sample of nodules. The data also indicated considerable variation in the proportions of strains in the nodules of individual plants.