Candidate codes in the gustatory system of caterpillars

Larvae of tobacco hornworms offer unique opportunities to relate the electrophysiological output of identified chemosensory neurons to specific behavioral responses. Larvae can discriminate among three preferred plants with only eight functioning gustatory receptors. They can be induced to prefer any one of the plants, and these preferences can be reversed. All eight neurons respond to each plant sap. Two fire too infrequently to permit detailed analysis. Analyses of the remaining six show that all electrophysiological responses consist of phasic and tonic components. Only the "salt best" cell fires during the phasic period. Temporal analysis of the spike train during this period shows that tomato and tobacco could be distinguished from Jerusalem cherry but not from each other by a rate code. Measurements of behavioral response times together with the nonspecificity of this with respect of food plants, unacceptable plants, and sodium chloride eliminate a phasic period rate code as a probable mechanism for complex discrimination. Events occurring in the tonic period, when all cells are firing, suggest a major role for this period. Analyses of variance in the interval frequencies of the large and medium spikes suggest that a variance code could allow discrimination among the three plants as long as both cells were firing at the same time. Evidence has been found for temporal patterning in the tonic response of the "salt best" cell to Jerusalem cherry but is absent elsewhere. The most likely basis for coding the difference between each of the three plants is across- fiber patterning in which the relative rates of firing and the variances of all the sensory neurons in the tonic phase are critical.     

Composite cylinder models of DNA: application to the electrostatics of the B-Z transition.

We develop and test a Poisson-Boltzmann model of the electrostatics of the B-Z transition of DNA. Starting from the detailed geometries of the two forms, we compute at each radius the fractions of DNA matter, of volume forbidden (for nonpoint-like ions), and of volume accessible to the center of ions. These radial distributions are incorporated in a composite cylinder model; availability to ions (porosity) and the dielectric constant at each radial distance are then obtained. The phosphate charge is distributed with cylindrical symmetry on two layers at the appropriate radial distances. The porous sheath, between the axis and the charge distribution, provides much more room for ions in B-DNA than in Z-DNA. By using previously developed methods, the Poisson-Boltzmann problem of such cylinders is easily solved. The computational load is small, so that results can be obtained for a large set of salt concentrations and for a number of ionic radii. The variation of the electrostatic free energy difference with salt concentration compares favorably with the experimental value (it is half as large). There is also qualitative agreement with experiments on supercoiled DNA, including a maximum of the free energy difference at submolar salt concentrations. The results for this cylinder with porous sheath are in line with those of the earlier simple planar model and of a plain cylinder with sheath, which is also presented here. They are thus insensitive to details of the model. They support the proposition that the main electrostatic feature of the B-Z transition is the better immersion of the B-DNA phosphates into the solution. They also give confidence in the validity of the Poisson-Boltzmann approach, despite the large salt concentrations involved. Prior studies using an approach based on the potential of mean force are discussed.     

The Extent of Protease Resistance of Misfolded Prion Protein Is Highly Dependent on the Salt Concentration

Transmissible spongiform encephalopathies are neurodegenerative diseases caused by prions in mammals. An aberrantly folded protein (PrP^Sc) is the main component of these proteinaceous infectious particles. Prions exhibit strong resistance to protease digestion, which is typically exploited for biochemical discrimination from its native cellular form (PrP^C). This classical feature has been partially challenged by the isolation of sizeable amounts of protease-sensitive PrP^Sc isoforms that self-propagate in vivo. Here, we report that the degree of PrP^Sc protease resistance is highly dependent on the concentration of salt in the solution. Similar changes were observed in PrP^Sc obtained from different strains and species. Strikingly, the effect of salt is reversible and is associated with changes on the size of PrP^Sc particles, but surprisingly, the more protease-sensitive species consists of a larger size. These findings shed light on the mechanistic aspects of prion proteolysis and should be considered when assessing samples of biomedical relevance.     

Lectins in the hemolymph of Japanese horseshoe crab, Tachypleus tridentatus

The hemolymph of the Japanese horsehoe crab, Tachypleus tridentatus contains lectins which agglutinate mammalian erythrocytes. Affinity chromatographic purification of the lectins using bovine submaxillary gland mucin-conjugated Sepharose resulted in the separation of the lectins into four fractions; one major and three minor lectins. Protein subunits revealed by polyacrylamide gel electrophoresis and the immunoprecipitin line of these lectins against antiserum to crude lectins were unique to each fraction. The activities of all the lectins were optimal at pH values between 6 and 8, and were destroyed by heating at 60°C. Calcium chloride augumented the activities of three lectins, but the major lectin was not influenced by the salt. Bovine erythrocytes were not agglutinated by any of the lectins and comparative agglutination titers for other erythrocytes from various sources were different among these lectins. The activities of all the lectins were inhibited by N-acetylamino sugars. They were more effectively inhibited by glycoproteins which contain sialic acid.     

Reverse lateralization of visual discriminative abilities in the European starling

Previous experiments on visual feature discrimination abilities have consistently shown a right-eye system lateralization in pigeons, Columba livia, and young domestic chickens, Gallus gallus domesticus, both nonpasserine species. Recently, however, it has been shown that photoreceptor distribution in the left and right retinas are asymmetrical in the European starling, Sturnus vulgaris, a passerine species. Single cone receptors are significantly more abundant in the left retina, which suggests that starlings should perform visual discrimination tasks more proficiently with the left eye, in contrast to previous findings with nonpasserines. We tested this hypothesis using the technique of monocular occlusion. In the first experiment, starlings were tested on a simultaneous visual discrimination task in three conditions: binocular (both eyes), left monocular (left eye only) and right monocular (right eye only). Subjects in the binocular and left-monocular conditions achieved significantly higher performance scores on the discrimination task than birds in the right-monocular condition. A second experiment found similar results, with birds in the left-monocular condition learning the discrimination task more than twice as quickly as those in the right-monocular condition. Subsequent tests with the alternative eye for both groups indicated no interocular transfer. These findings suggest that visual discriminative abilities in starlings are asymmetrical, and that they are lateralized in the opposite eye system than has been reported for all other species tested to date.     

两种抗生素对龙须菜的光合生理效应

探讨了不同浓度的两种抗生素(氯霉素和青霉素G钠)对龙须菜(Gracilaria lemaneiformis)生长、光合作用、呼吸作用、色素含量以及可溶性蛋白含量等生理特性的影响。结果表明:龙须菜的生长受到两种抗生素的影响,但是氯霉素的影响要比青霉素G钠的影响大的多。在氯霉素处理的过程中,光合作用、有效光化学效率(Yield)、藻红藻蓝蛋白以及可溶性蛋白含量都随着氯霉素浓度的升高而显著下降,但是呼吸作用速率由于氯霉素的处理而升高;此外光合色素含量不受氯霉素的影响。在青霉素G钠的处理中,光合作用、有效光化学效率随着青霉素G钠的升高而下降,龙须菜叶绿素a与类胡萝卜素含量随着青霉素G钠浓度的升高而具有升高的趋势,但藻红蛋白、藻蓝蛋白以及可溶性蛋白在各处理组之间均没有表现出一定趋势。这些结果说明,氯霉素对生长的影响主要是光合作用速率的下降,以及有关蛋白合成下降引起,而青霉素G钠对生长的影响可能原因是呼吸作用速率的增加引起。由于龙须菜对氯霉素的敏感性比对青霉素G钠的敏感性更强,氯霉素在基因工程的育种中可能更适合作为选择压力。     

Intra- and interspecific host discrimination in Asobara (Hymenoptera) larval endo-parasitoids of Drosophilidae: Comparison between closely related and less closely related species

Host discrimination studies were conducted with different species of Asobara, which are larval endo-parasitoids of Drosophilidae. Results indicated variable host discrimination which depended on the relatedness of the species. The closely related sibling species Asobara tabida (Nees) and A. rufescens (Foerster) were not only capable of intraspecific discrimination, but also avoided multiparasitism by discriminating between unparasitized host larvae and larvae previously parasitized by females of the other species. This ability to discriminate interspecifically does not seem functional as each species occupies its own microhabitat. As it was shown to be absent in less closely related Asobara species we concluded that interspecific discrimination by A. tabida and A. rufescens was due to their close relationship.     

Nonelemental visual learning in honeybees

Free-flying honeybees, Apis mellifera, learn visual stimuli in the appetitive context of food search. Visual compound stimuli are relevant in nautre as bees learn flower images that consist of many visual elements. We studied whether elemental associations between each visual element and the reinforcement (elemental approach) are enough to explain the solving of visual discrimination problems that raise ambiguity at the elemental level. We asked whether bees could solve three different visual discriminations: (1) positive patterning (A−, B−, AB+); (2) negative patterning (A+, B+, AB−); and (3) biconditional discrimination (AB+, CD+, AC−, BD−). In experiments 1 and 2 bees had to discriminate a yellow-violet chequerboard from the yellow or the violet squares alone. In experiment 3, four different gratings combining one colour (yellow or violet) with one orientation (vertical or horizontal) had to be discriminated. In all three problems binary compounds were trained in such a way that each element appeared equally often as rewarded and nonrewarded. Bees could solve the three discrimination problems. They always chose the reinforced stimulus despite ambiguity at the level of the elements. For solving positive patterning, elemental processing could be used. For negative patterning and biconditional discrimination, nonelemental processing strategies (unique-cue or configural approach) are necessary to account for these results. Although we cannot decide between a configural and a unique-cue interpretation, we can clearly reject purely elemental processing in these cases. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Genotypic Responses to Salinity: Differences between Salt-sensitive and Salt-tolerant Genotypes of the Tomato

Four ecotypes of the species Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull. from the Galapagos Islands were compared with L. esculentum Mill cv. VF 36 with respect to salt tolerance. The L. cheesmanii ecotype that proved most salt-tolerant was selected for detailed comparison with the L. esculentum cultivar. Plants were grown in modified Hoagland solution salinized with synthetic seawater salt mix. Growth rates under saline conditions were examined and amino acid, sugar, total amino nitrogen, free acidity, and Na and K levels in the tissues of the most and least tolerant plants were measured under salt stress and nonstress conditions. Results indicate that all Galapagos ecotypes were far more salt-tolerant than was the esculentum cultivar. They could survive in full strength seawater nutrient solution while the esculentum cultivar could not in most cases withstand levels higher than 50% seawater. Growth rates were reduced in both species under saline conditions but the esculentum cultivar was more severely affected. High levels of total amino nitrogen, specific amino acids, and free acidity along with low sodium content were found in the salt stressed VF 36 cultivar. The opposite responses were noted in the salt stressed treatments of the Galapagos ecotype. Tissue sugar levels did not appear to be similarly correlated with salt stress in either species. Potassium content fell sharply during salinization in the Galapagos ecotype while in the esculentum cultivar it declined relatively little even at high levels of salinity.     

Adaptation to a novel host modifies host discrimination by the seed beetle Callosobruchus maculatus

Females of the seed beetle Callosobruchus maculatus avoid adding eggs to seeds that already bear eggs. Geographical variation in this behaviour has been thought to depend on differences in host size. In populations that attack small-seeded legumes, only one or two larvae can develop within a seed, and females are especially adept at detecting and rejecting occupied (egg-laden) seeds. We performed a mass-selection experiment in which replicate lines of a population associated with a small host (mung bean, Vigna radiata) were either maintained on this host or were transferred to a larger host (cowpea, Vigna unguiculata) that can support several larvae per seed. After more than 40 generations, we estimated the strength of host discrimination by presenting females a choice of egg-free and egg-laden seeds, and by quantifying how uniformly females spread their eggs among egg-free seeds. Compared to females maintained on mung bean, females from cowpea lines were more likely to accept occupied seeds in choice tests. They also distributed their eggs less uniformly, especially when cowpea served as the test host. Cowpea lines thus evolved to resemble populations that have long been associated with the larger host. A separate study showed that weaker host discrimination in the cowpea lines was accompanied by a decline in larval competitiveness, which may have further relaxed selection for avoidance of occupied hosts. Our results demonstrate that switching to a novel resource can produce rapid and predictable changes in a fitness-related insect behaviour. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Population dynamics of annual Salicornia species in the tidal salt marshes of the Oosterschelde,The Netherlands

1. The population dynamics of two Salicornia species from the Bergen op Zoom salt marsh (south-west Netherlands) was examined. Based on the results of several field studies three preliminary life tables were constructed, two for S. procumbens agg. populations growing respectively on the mud flats and in the salt marsh, and one for S. europaea agg. living in the upper marsh.
2. The life cycles are described and quantified in terms of eight phases and the transition probabilities between them, starting from a notional individual representative of each population.
3. The models depicting the life cycle of S. procumbens show a mean offspring number of 4.26 individuals per parent for the mud-flat population and 0.18 for the salt-marsh population. The S. europaea model gives an output of 0.44 individuals per parent. These results reflect the fluctuations in population size observed in sample plots over the years 1976–78.
4. Comparison of the transition probabilities reveals that on the mud flats most S. procumbens individuals die during pollination and seed germination, while the population in the salt marsh proper is thinned especially during the seed phase in winter time and during the growth from established seedlings to maturation. S. europaea behaves in a similar but less pronounced way to S. procumbens in the salt marsh.
5. Probabilities for one flower or one seed to produce a mature flowering plant were calculated, and were compared with those found in the literature. They are roughly of the same order of magnitude as the probabilities for other annual species, but much higher than those reported for biennial species.

     

Canopy spectral characteristics of typical invasive and native plants in the coastal wetland of Yancheng City,China

Spartina alterniflora (S. alterniflora) is a dominant invasive alien species that occurs in Yancheng Wetland National Nature Reserve, the largest coastal wetland in China. It expands rapidly and exerts great threats to local ecosystem. The main native species there are Phragmites australis (P. australis) and Suaeda salsa (S. salsa), respectively. In order to monitor their dynamics, it is of great significance to analyze their spectral discrimination. Canopy spectra of these typical species were measured in July and October in order to compare species differences, as well as the seasonal variation. The Normalized Difference Vegetation Index (NDVI) was calculated based on canopy spectra. The significances of differences in spectral characteristic among species were tested using the one-way analysis of variance (ANOVA) (P < 0.05). The results showed that the visible (VI) bands were the optimum wavelengths for species discrimination in both seasons. S. alterniflora always had the greatest green peak height and red absorption depth. S. salsa had no obvious green peak, but an obvious red reflection peak. P. australis generally had intermediate values. Spectra in the near-infrared (NIR) bands were not appropriate for delineating S. alterniflora and P. australis in summer, as they showed similar values in these wavelengths. But NIR bands could be used to distinguish S. salsa in summer, as it had significantly lower reflectance in NIR bands than the others. Meanwhile, the reflectance in short-wavelength infrared (SWIR) bands became another suitable approach for distinguishing species in autumn. S. salsa had significantly higher values than the others in SWIR regions. Significant NDVI differences between different species proved that it could improve the species discrimination. S. alterniflora always had the highest NDVI values, while S. salsa had the lowest values. The seasonal trend of canopy spectra was also revealed. With plant maturity, the reflectance values in green bands and NIR bands decreased significantly, but increased significantly around the yellow-red wavelengths. The green peak heights, red absorption depths, and NDVI values of the species decreased remarkably. Furthermore, S. alterniflora and P. australis illustrated obvious ‘blue shift’ of the red edge with senescence. These results pointed out the the potential bands and appropriate spectral parameters appropriate for species discrimination, and highlighted the influence of seasonality on spectral information. They provided an important basis for salt marshes identification and dynamic monitoring on a large scale.     

Temperature-induced lipocalin (TIL) is translocated under salt stress and protects chloroplasts from ion toxicity

Temperature-induced lipocalins (TIL) have been invoked in the defense from heat, cold and oxidative stress. Here we document a function of TIL for basal protection from salinity stress. Heterologous expression of TIL from the salt resistant poplar Populus euphratica did not rescue growth but prevented chlorophyll b destruction in salt-exposed Arabidopsis thaliana. The protein was localized to the plasma membrane but was re-translocated to the symplast under salt stress. The A. thaliana knock out and knock down lines Attil1-1 and Attil1-2 showed stronger stress symptoms and stronger chlorophyll b degradation than the wildtype (WT) under excess salinity. They accumulated more chloride and sodium in chloroplasts than the WT. Chloroplast chloride accumulation was found even in the absence of salt stress. Since lipocalins are known to bind regulatory fatty acids of channel proteins as well as iron, we suggest that the salt-induced trafficking of TIL may be required for protection of chloroplasts by affecting ion homeostasis.     

Salt tolerance in the halophyte Salicornia dolichostachya Moss: Growth,morphology and physiology

Salinization of agricultural land is an increasing problem. Because of their high tolerance to salinity, Salicornia spp. could become models to study salt tolerance; they also represent promising saline crops. The salinity-growth response curve for Salicornia dolichostachya Moss was evaluated at 12 salt concentrations in a hydroponic study in a greenhouse and at 5 different seawater dilutions in an outside setting. Salt concentrations ranged between 0 mM and 500 mM NaCl (≈seawater salinity). Plants were grown for six weeks and morphological and physiological adaptations in different tissues were evaluated.S. dolichostachya had its growth optimum at 300 mM NaCl in the root medium, independent of the basis on which growth was expressed. The relative growth rate (RGR) in the greenhouse experiment was comparable with RGR-values in the outdoor growth experiment. Leaf succulence and stem diameter had the highest values at the growth optimum (300 mM NaCl). Carbon isotope discrimination (δ¹³C) decreased upon salinity. S. dolichostachya maintained a lower leaf sap osmotic potential relative to the external solution over the entire salinity range, this was mainly accomplished by accumulation of Na⁺ and Cl⁻. Glycine betaine concentrations did not significantly differ between the treatments. Na⁺:K⁺-ratio and K⁺-selectivity in the shoots increased with increasing salinity, both showed variation between expanding and expanded shoot tissue. We conclude that S. dolichostachya was highly salt tolerant and showed salt requirement for optimal growth. Future growth experiments should be done under standardized conditions and more work at the tissue and cellular level needs to be done to identify the underlying mechanisms of salt tolerance.     

Three processing characteristics of visual texture segmentation

Three mechanisms are outlined which are sufficient to determine texture segmentation or discrimination. They are: (1) convolution of detector profiles with the input image; (2) impletion, where the perceptual 'filling in' of the input surface occurs via a nonlinear filtering operation on each detector's output (3) grouping, where areas are segregated according to their differences in detector responses after impletion occurs. These mechanisms are compared with those proposed to occur in human visual texture discrimination.     

An Analysis of Hamster Afferent Taste Nerve Response Functions

Sensitivities to moderately intense stimuli representing four taste qualities to man were determined for 79 hamster chorda tympani fibers. Some fibers were very sensitive to sucrose, sodium chloride, or hydrochloric acid, but none were very sensitive to quinine. These sensitivities were not randomly distributed among fibers: the sucrose sensitivity was separated from and negatively correlated with the other sensitivities which were associated and positively correlated with each other. Moreover, there were a limited number of sensitivity patterns: (a) fibers responding best to sucrose responded second-best to salt, less to acid, not to quinine; (b) fibers responding best to salt either responded second-best to sucrose and not to acid or quinine; or second-best to acid, less to quinine, and not to sucrose; and (c) fibers responding best to acid responded second-best to salt, more to quinine, and less to sucrose than other fibers. Therefore, if four stimuli of different taste qualities are ordered from acceptable to unacceptable, neural response functions of most hamster chorda tympani taste fibers peak at one point. Sensitivities to nine other moderately intense stimuli which vary in quality to man were also determined for 46–49 of the fibers. Sensitivities to sweet stimuli were always associated with each other and separated from sensitivities to nonsweet stimuli. Sensitivities to nonsweet stimuli were all associated with each other; however, the strongest correlations were between sensitivities to stimuli of like quality, e.g., the three acids or the two sodium salts.     

Investigating social discrimination of group members by laying hens

Social relationships in domestic fowl are commonly assumed to rely on social recognition and its pre-requisite, discrimination of group-mates. If this is true, then the unnatural physical and social environments in which commercial laying hens are typically housed, when compared with those in which their progenitor species evolved, may compromise social function with consequent implications for welfare. Our aims were to determine whether adult hens can discriminate between unique pairs of familiar conspecifics, and to establish the most appropriate method for assessing this social discrimination. We investigated group-mate discrimination using two learning tasks in which there was bi-directional exchange of visual, auditory and olfactory information. Learning occurred in a Y-maze task (p < 0.003; n = 7/8) but not in an operant key-pecking task (p = 0.001; n = 1/10). A further experiment with the operant-trained hens examined whether failure was specific to the group-mate social discrimination or to the response task. Learning also failed to occur in this familiar/unfamiliar social discrimination task (p = 0.001; n = 1/10). Our findings demonstrate unequivocally that adult laying hens kept in small groups, under environmental conditions more consistent with those in which sensory capacities evolved, can discriminate group members: however, appropriate methods to demonstrate discrimination are crucial.     

Isolation and characterization of Zygosaccharomyces rouxii mutants defective in proton pumpout activity and salt tolerance

Two mutants defective in salt tolerance were identified among hygromycin B (HygB)-resistant mutants of Zygosaccharomyces rouxii. These mutants showed different phenotypes in terms of sensitivity towards high concentrations of glucose and KCl. Recovery of salt tolerance by the addition of KCl and CaCl₂ or by lowering pH (pH 4.0) was different for the two mutants. Moreover, both mutants showed lowered plasma membrane (PM-) ATPase activity and proton pumpout activity. They exhibited neither growth nor proton pumpout activity in a medium containing 5% NaCl. The proton pumpout activity was inhibited by vanadate, an inhibitor of PM-ATPase, only when cells were incubated in the presence of more than 1% NaCl. Damage of the proton pumpout activity seems to be the reason for the salt sensitivity of both mutants. We showed that it was essential for Z. rouxii cells to pump out protons under a high salt environment using mutants defective in this ability.     

THREE SCALING METHODS FOR CONSUMER RATING OF SALT INTENSITY

This study aimed to identify a scaling technique, which would offer the greatest degree of discrimination and accuracy in an evaluation of soup samples, varying in salt concentration (0.3, 0.8 and 1.3% salt). A Seven Point Category Scale, a 100 mm Line scale and non-modulus Magnitude Estimation were used to evaluate samples by consumers (n = 36).
A Friedman Two-Way ANOVA and a Wilcoxon Signed Ranks test were applied to the data to compare discriminatory ability and accuracy of the scaling techniques. Results revealed that each of the techniques could be used to discriminate between samples (P<0.001). However, none of the three techniques were significantly more accurate than one another. In view of the results and consumer preference/comments for using the Seven Point Category Scale, this technique is proposed as an effective method for consumer rating of salt intensity.     

RNA from callus cultures and leaves of Nicotiana tabacum

MAK column chromatography has been used to analyse RNA from normal and crown gall callus cultures and leaves of Nicotiana tabacum. To determine the elution behaviour of well-defined DNA-like RNAs with different GC content, complementary RNAs (c-RNA) synthesized on Agrobacterium tumefaciens DNA and crown gall DNA were used. The elution profile of the RNA from all three tissues followed a similar pattern. By salt gradient elution the RNA in the tRNA region showed a remarkably high CMP content which was significantly higher for the normal tissues than for crown gall tissue. RNA from the callus cultures contained more DNA-like RNA (D-RNA) with a higher turnover rate than RNA from leaves. Because of its relatively low poly A content, measured as RNase A + T₁ resistance, as well as its high turnover rate, the salt-eluted D-RNA is thought to be heterogeneous nuclear RNA (Hn-RNA) and not mRNA. RNA molecules that might represent the mRNA population, having intramolecular poly A tracts, were subsequently eluted by a salt gradient, a low salt buffer and with the chaotropic agent guanidine thiocyanate, which removed tenaciously bound (TB-RNA) in two fractions, α and β. Crown gall RNA showed both a different labelling behaviour and a higher poly A content in the α and β fractions compared to the normal tissues. c-RNAs may be eluted at different salt concentrations because of their different GC content. They give rise to a considerable fraction of TB-RNA which in the presence of tobacco leaf RNA was split into fractions similar to α and β. No fraction was found amongst these RNAs which did have intramolecular poly A tracts.