Divergent responses of two cereal aphids to previous infestation of their host plant

The role of pollen odour in resource location by the pollen beetle, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), a pollen-feeding insect regarded as a pest of oilseed rape, Brassica napus L., (Brassicaceae) crops, was investigated in a linear track olfactometer. Both male and female beetles were attracted to the odour of whole oilseed rape flowers, indicating that these insects can locate their host plants using floral odours as cues. The attractive odour of flowers was found to emanate from all floral parts tested: the petals/sepals, the anthers, and from pollen itself. Therefore, at least part of the attractive odour of oilseed rape flowers emanates from pollen. Beetles were more attracted to floral samples containing anthers than those without anthers when these odours were directly compared in a choice-test, and this indicates that there were detectable differences between them. Anthers and pollen may therefore release distinctive odours that are quantitatively and/or qualitatively different from the odour of the rest of the flower. These experiments support the hypothesis that pollen-seeking insects use pollen odour cues to locate this food source.     

Cross-modal associations of human body odour attractiveness with facial and vocal attractiveness provide little support for the backup signals hypothesis: A systematic review and meta-analysis

Assessing the attractiveness of potential mating partners typically involves multiple sensory modalities, including the integration of olfactory, visual, and auditory cues. However, predictions diverge on how the individual modalities should relate to each other. According to the backup signals hypothesis, multimodal cues provide redundant information, whereas the multiple messages hypothesis suggests that different modalities provide independent and distinct information about an individual's mating-related quality. The backup signals hypothesis predicts a positive association between assessments based on different modalities, whereas no substantial correlation across modalities is expected under the multiple messageshypothesis. Previous studies testing the two hypotheses have provided mixed results, and a systematic evaluation is currently missing.We performed a systematic review and a meta-analysis of published and unpublished studies to examine the congruence in assessments between human body odour and facial attractiveness, and between body odour and vocal attractiveness. We found positive but weak associations between ratings of body odours and faces (r = 0.1, k = 25), and between body odours and voices (r = 0.1, k = 9). No sex differences were observed in the magnitude of effects.Compared to judgments of facial and vocal attractiveness, our results suggest that assessment of body odour provides independent and non-redundant information about human mating-related quality. Our findings thus provide little support for the backup signals hypothesis and may be better explained by the multiple messages hypothesis.     

The Influence of Light Intensity on the Activation and Operation of the Hydroxyl Efflux System of Chara corallina

The interrelationships between light intensity and the activationof OH^– bands was investigated. The lag period prior toOH^– efflux activation was longer than the photosyntheticinduction period. It was found that this lag period dependedupon the light regime employed as well as the photosyntheticcapacity of the cell. The response of the cell to low light intensities revealed thatall OH^– bands were not of equal status. Below a criticallight intensity the cell did not develop any bands even afterprolonged illumination. An hypothesis is presented to accountfor these results, interms of total cell OH^– band activationand the regulation of the HCO₃^– and OH^– transportsystems. It is proposed that the electrical properties of theChara corallina plasmalemma, observed at high pH values, canbe explained on the basis of the hypothesis presented in thispaper     

Several models of suprathreshold quantitative olfactory interaction in humans applied to binary, ternary and quaternary mixtures

Performances were compared of several mathematical models forprediction of the perceived odour intensities of odorant mixturesfrom the odour intensities and some other related propertiesof the components. The models included Berglund's vectorial,an extension of the U model proposed by Patte and Laffort, aUPL model which utilizes exponents of the psychophysical powerlaw, and some simplified models. Data for the model testingwere obtained from literature and from new experimental measurementsin which the odour intensity of vapours of 28 odorous substancesand their 168 binary, 112 ternary, and 28 duplicated quaternarymixtures were matched vs. 1-butanol. The best performance onthe literature data, which have been obtained by the magnitudeestimation methods, was shown by the U model. The best performanceon the new data obtained by the butanol scale method was bythe simplified vectorial and U models; these used constant valuesof the interaction term cos . ^*Presented in a condensed form at the 3rd Congress of ECRO,Pavia, Italy, and in J. Physiol. (Paris), 1978, 74, 19A.     

MHC isoform composition and Ca(2+)- or Sr(2+)-activation properties of rat skeletal muscle fibers

Chemically skinned single fibers from adult rat skeletalmuscles were used to test the hypothesis that, in mammalian muscle fibers, myosin heavy chain (MHC) isoform expression andCa²⁺- or Sr²⁺-activation characteristics areonly partly correlated. The fibers were first activated inCa²⁺- or Sr²⁺-buffered solutions undernear-physiological conditions, and then their MHC isoform compositionwas determined electrophoretically. Fibers expressing only the MHC Iisoform could be appropriately identified on the basis of either theCa²⁺- or Sr²⁺-activation characteristics or theMHC isoform composition. Fibers expressing one or a combination of fastMHC isoforms displayed no significant differences in theirCa²⁺- or Sr²⁺-activation properties; therefore,their MHC isoform composition could not be predicted from theirCa²⁺- or Sr²⁺-activation characteristics. Alarge proportion of fibers expressing both fast- and slow-twitch MHCisoforms displayed Ca²⁺- or Sr²⁺-activationproperties that were not consistent with their MHC isoform composition;thus both fiber-typing methods were needed to fully characterize suchfibers. These data show that, in rat skeletal muscles, the extent ofcorrelation between MHC isoform expression and Ca²⁺- orSr²⁺-activation characteristics is fiber-type dependent.

     

Endogenous and exogenous cardiac glycosides: their roles in hypertension, salt metabolism, and cell growth

Cardiotonic steroids (CTS), long used to treat heart failure, are endogenously produced in mammals. Among them are the hydrophilic cardenolide ouabain and the more hydrophobic cardenolide digoxin, as well as the bufadienolides marinobufagenin and telecinobufagin. The physiological effects of endogenous ouabain on blood pressure and cardiac activity are consistent with the "Na⁺-lag" hypothesis. This hypothesis assumes that, in cardiac and arterial myocytes, a CTS-induced local increase of Na⁺ concentration due to inhibition of Na⁺/K⁺-ATPase leads to an increase of intracellular Ca²⁺ concentration ([Ca²⁺]_i) via a backward-running Na⁺/Ca²⁺ exchanger. The increase in [Ca²⁺]_i then activates muscle contraction. The Na⁺-lag hypothesis may best explain short-term and inotropic actions of CTS. Yet all data on the CTS-induced alteration of gene expression are consistent with another hypothesis, based on the Na⁺/K⁺-ATPase "signalosome," that describes the interaction of cardiac glycosides with the Na⁺ pump as machinery activating various signaling pathways via intramembrane and cytosolic protein-protein interactions. These pathways, which may be activated simultaneously or selectively, elevate [Ca²⁺]_i, activate Src and the ERK1/2 kinase pathways, and activate phosphoinositide 3-kinase and protein kinase B (Akt), NF-B, and reactive oxygen species. A recent development indicates that new pharmaceuticals with antihypertensive and anticancer activities may be found among CTS and their derivatives: the antihypertensive rostafuroxin suppresses Na⁺ resorption and the Src-epidermal growth factor receptor-ERK pathway in kidney tubule cells. It may be the parent compound of a new principle of antihypertensive therapy. Bufalin and oleandrin or the cardenolide analog UNBS-1450 block tumor cell proliferation and induce apoptosis at low concentrations in tumors with constitutive activation of NF-B. endogenous cardiotonic steroids; ouabain; marinobufagenin; rostafuroxin; bufalin; oleandrin; sodium pump; sodium/potassium-adenosinetriphosphatase; arterial hypertension; sodium metabolism; cell proliferation; cancer therapy     

How cross-modality effects during intraspecific interactions of jumping spiders differ depending on whether a female-choice or mutual-choice mating system is adopted

An important prediction from game theory is that the value of a resource influences the level to which conflict escalates. Here we use jumping spiders (Salticidae) to consider this prediction in the context of species adopting different mating systems (‘female mate-choice’ and ‘mutual mate-choice’). Our experiments are designed for determining whether the odour of conspecific females, more than the odour of heterospecific females, primes males to escalate conflict with a potential same-sex rival and also whether the odour of conspecific males, more than the odour of heterospecific males, primes females to escalate conflict with a potential same-sex rival. Four species were studied: Evarcha culicivora, a species in which mutual mate-choice is pronounced, and Portia fimbriata, Portia africana, and Jacksonoides queenslandicus, more conventional salticids in which female mate-choice and male–male competition appear to be dominant. Our hypothesis is that, for all four species, there is strong competition between males for access to females and that, for E. culicivora, but not for the other three species, there is also strong competition between females for access to males. Our findings are consistent with this hypothesis, as we show that, although the odour of conspecific females primes escalation of vision-based male–male conflict for all four species, E. culicivora is the only species for which there is evidence of odour from conspecific males priming the escalation of female–female conflict.     

Shear stress effects on cell growth and <Emphasis Type="SmallCaps">L</Emphasis>-DOPA production by suspension culture of <Emphasis Type="Italic">Stizolobium hassjoo</Emphasis> cells in an agitated bioreactor

Suspension cultures of Stizolobium hassjoo cells were cultivated in a 7l bioreactor. The growth rate and intracellular L-DOPA content of the cells using two different turbine impellers were compared. There were distinct differences in growth behavior and L-DOPA productivity in the range of 100 to 500 rpm for flat-blade turbine impeller. Disk turbine retarded significantly the cell growth but not so significantly for L-DOPA production in the range of 200 to 300 rpm. The shear force intensity of the two impellers at various rotational rates was compared with shear force index (SFI), and power input per unit mass and eddy length scale. There was good consistency among the three indexes for shear force intensity. Thus with SFI the shear force intensity of bioreactor can be indirectly estimated. A critical shear stress that may cause sublytic effect in cells was identified for flat-blade turbine operated at 400 rpm. The common effect between the shear stress and the proton elicitation in the bioreactor was elucidated with a hypothesis of signal transduction by second messenger, H⁺. Our results suggested that H⁺ transduced the signal to protoplast when S. hassjoo cells were stimulated by shear stress. This resulted in an increase of H⁺ which triggered a similar reaction to the pH control of culture broth and enhanced the L-DOPA production.     

Studies on the distribution of 14C-malformin A in major fractions of Phaseolus vulgaris L.

The distribution pattern of ¹⁴C-malformin in major fractionsof Phaseolus vulgaris L. seedlings shifted during water treatmentin the absence of malformin. From these shifts, and by comparisonof the ¹⁴C distribution patterns at the base and top of theseedlings, it was concluded that some ¹⁴C-malformin enters thecell and proceeds to the cell wall via intermediate compounds.As a working hypothesis it was suggested that in roots ¹⁴C-malforminfirst appears in a soluble "small molecules" fraction, bindsto a soluble protein fraction, and proceeds via die wall lipidfraction to the wall itself. Direct binding of some ¹⁴C-malforminto the wall fraction was not precluded. In leaves, the pathwayof ¹⁴C-malformin to the cell wall was similar in some respectsto that in roots. ¹ Present address: American Cyanamid, P.O. Box 400, Princeton,New Jersey 08540, U.S.A. (Received January 21, 1976; )     

A comparison of nitrate transport in four different rice (Oryza sativa L.) cultivars

As rice can use both nitrate (NO₃^-) and ammonium (NH₄⁺), we have tested the hypothesis that the shift in the pattern of cultivars grown in Jiangsu Province reflects the ability of the plants to exploit NO₃^- as a nitrogen (N) source. Four rice cultivars were grown in solution culture for comparison of their growth on NO₃^- and NH₄⁺ nitrogen sources. All four types of rice, Xian You 63 (XY63), Yang Dao 6 (YD), Nong Keng 57 (NK) and Si You 917 (SY917), grew well and produced similar amounts of shoot biomass with 1 mmol/L NH₄⁺ as the only N source. However, the roots of NK were significantly smaller in comparison with the other cultivars. When supplied with 1 mmol/L NO₃^-, YD produced the greatest biomass; while NK achieved the lowest growth among the four cultivars. Electrophysiological measurements on root rhizodermal cells showed that the NO₃^--elicited changes in membrane potential (ΔE_m) of these four rice cultivars were significantly different when exposed to low external NO₃^- (<1 mmol/L); while they were very similar at high external NO₃^- (10 mmol/L). The root cell membrane potentials of YD and XY63 were more responsive to low external NO₃^- than those of NK and SY917. The ΔE_m values for YD and XY63 rhizodermal cells were almost the same at both 0.1 mmol/L and 1 mmol/L NO₃^-; while for the NK and SY917 the values became larger as the external NO₃^- increased. For YD cultivar, ΔE_m was measured over a range of NO₃^- concentrations and a Michaelis-Menten fit to the data gave a K_m value of 0.17 mmol/L. Net NO₃^- uptake depletion kinetics were also compared and for some cultivars (YD and XY63) a single-phase uptake system with first order kinetics best fitted the data; while other cultivars (ND and SY917) showed a better fit to two uptake systems. These uptake systems had two affinity ranges: one had a similar K_m in all the cultivars (0.2 mmol/L); the other much higher affinity system (0.03 mmol/L) was only present in NK and SY917. The expression pattern of twelve different NO₃^- transporter genes was tested using specific primers, but only OsNRT1.1 and OsNRT2.1 expression could be detected showing significant differences between the four rice cultivars. The results from both the physiological and molecular experiments do provide some support for the hypothesis that the more popular rice cultivars grown in Jiangsu Province may be better at using NO₃^- as an N source.     

The vitamin B requirement of Phaeocystis globosa (Prymnesiophyceae)

In batch cultures of flagellates and non-flagellate cells ofPhaeocystis globosa, the biomass yield was significantly enhancedby the addition of a mixture of the vitamins thiamine (B1),cyanocobalamin (B12) and biotin (H). A bioassay with B1 andB12 using the non-flagellate cells of P.globosa showed thatthis prymnesiophyte is a B1 auxotroph. The bioassay also indicateda significant difference in growth rate between culture mediumwith 10 nmol l^–1 B1 (µ = 0.80 day^–1) and culturemedium with 10 nmol l^–1 B12 (µ = 0.52 day^–1).These findings are discussed in relation to the hypothesis thatcentric diatoms, through vitamin B1 excretion or B12 depletion,initiate Phaeocystis blooms. It is concluded, however, thatan alternative hypothesis, that diatoms provide a solid substratefor colony initiation, has more experimental support.     

Individual Odour Similarity and Discrimination in the Coruro (Spalacopus cyanus, Octodontidae)

Previous studies of subterranean, fossorial and above‐ground rodents have demonstrated that similarities in individual odours covary with genetic similarities thus supporting the theory of odour‐genes covariance (i.e. the closer the individuals are genetically, the greater the similarities between their odours). We used the habituation‐generalization paradigm, where the subject is exposed to the same odour stimulus in three consecutive habituation trials followed by two test trials in which the odour from two other individuals are presented successively. Using this test design, we showed that the socially living coruros (Spalacopus cyanus) discriminate individuals on the basis of their ano‐genital odours and also respond to odour similarities between individuals. Male and female subjects treated ano‐genital odours of two same‐sex family members and also the odours of two sibling strangers as different to each other. At the same time, they treated the odours of siblings as similar compared with the odour of an unrelated individual. No gender differences were detected. Our results contrast with those from other rodent species that did not spontaneously discriminate between individual odours of siblings from a different family than their own. The polygyneous lifestyle may provide the selective background for that difference. Additional research will be necessary to explore this hypothesis and to rule out differences due to dietary preferences and due to the type of paradigm chosen for the tests.     

The Conversion of 3-Indolylmethylglucosinolate to 3-Indolylacetonitrile by Myrosinase, and its Relevance to the Clubroot Disease of the Cruciferae

[Methylene-¹⁴C]-3-indolylmethylglucosinolate (¹⁴C-IMG) was convertedin vitro to [methylene-¹⁴Cl-3-indolylacetonitrile (¹⁴C-IAN)by myrosinase over a pH range of 4.0-6.0 and this conversionwas enhanced by ferrous ions. Other products of the reactionincluded 3-indolylmethanol, 3, 3'-diindolylmethane and ascorbigenA. Trace amounts of ¹⁴C-IAN were produced non-enzymically from¹⁴C-IMG in the presence of ferrous ion over a similar _pH range.Furthermore, swede tissues (Brassica napus cv. Danestone) infectedwith Plasmodiophora brassicae Woron. could convert ¹⁴C-IMG to¹⁴C-IAN. These results were consistent with the hypothesis thatthe overgrowth symptoms of the clubroot disease are caused bythe conversion of IMG to the auxin precursor IAN.     

Sex differences in olfaction‐mediated visual acuity in blowflies and its consequences for gender‐specific trapping

The behaviour of 650 female Calliphora vicina Robineau‐Desvoidy (Diptera: Calliphoridae) was examined in a wind tunnel using odour, in combination with six artificial visual stimuli, ranging from a simple black square to a three‐dimensional model of a dead mouse. The carcasses of laboratory mice were used to provide a natural odour and visual source, and a blend consisting of dimethyl trisulphide, mercaptoethanol, and o‐cresol was used to provide a synthetic lure. Significant differences were found in attraction to these odour sources: 90% of the flies oriented upwind to the natural source and 62% to the synthetic lure. No significant differences were found in upwind orientation towards different visual stimuli, but flies showed significantly more landings if the visual cues provided a vertical contrast against the background. A horizontal contrast gave no difference in landing rate compared to treatments without visual cues. In a field study, the blowfly genera Pollenia, Calliphora, and Lucilia were caught. The overall blowfly catch was significantly higher when an odour lure was present (Pollenia: 3×, Calliphora: 15×, Lucilia: >79×). A significant three‐way interaction between visual cue, genus, and gender was found. The saprophagous Lucilia and Calliphora showed a gender‐specific response to visual stimuli, whereas the parasitic Pollenia did not. A 2:1 female:male sex ratio was found for Calliphora spp. and a 12:1 sex ratio for Lucilia spp. The data suggest that landing responses of male and female saprophagous blowflies, and consequently trap catches, result from olfaction, but also from gender‐specific visual responses when under the influence of odour.     

86Rb Influx in Maize Roots at Different External Concentrations of RbCl or KCl

Studies on ⁸⁶Rb influx in root segments of maize at differentexternal concentrations of KC1 or RbCl showed that there wasa preference for K⁺ over Rb⁺ at relatively low external concentrationsor when Fusicoccin was present. Experimental evidence supportsthe hypothesis that discrimination takes place when the ionuptake is energy-dependent. (Received September 6, 1982; Accepted December 7, 1982)     

Mechanism of the exercise hyperkalemia: an alternate hypothesis

Wasserman, Karlman, William W. Stringer, Richard Casaburi,and Yong-Yu Zhang. Mechanism of the exercisehyperkalemia: an alternate hypothesis. J. Appl.Physiol. 83(2): 631-643, 1997.A progressivehyperkalemia is observed as exercise intensity increases. The currentmost popular hypothesis for the hyperkalemia is that theNa⁺-K⁺pump cannot keep pace with the K⁺efflux from muscle during the depolarization-repolarization process ofthe sarcolemmal membrane during muscle contraction. In this report, wepresent data that suggest an alternate hypothesis to those previouslydescribed. Because phosphocreatine (PCr) is a highly dissociated acidand creatine is neutral at cell pH, the concentration of nondiffusibleanions decreases, and an alkaline reaction takes place when PCrhydrolyzes. This creates a state of cation(K⁺) excess andH⁺ depletion in the cell. Toexamine the balance of K⁺ andH⁺ for exercising muscle duringthe early period of exercise when PCr changes most rapidly, catheterswere inserted into the brachial artery and femoral vein (FV) in fivehealthy subjects who performed two 6-min cycle ergometer exercise testsat 40 and 85% of peak oxygen uptake. FV blood was sampled every 5 sduring the first 2 min, then every 30 s for the remaining 4 min ofexercise and the first 3 min of recovery, and then less frequently forthe next 12 min. Arterial sampling was every 30 s during exercise andsimultaneous with FV sampling during recovery. ArterialK⁺ concentration([K⁺]) increase laggedFV [K⁺]increase. The hyperkalemia observed during early exerciseresults from K⁺ release fromskeletal muscle. FV[K⁺] increased by 5 sof the start of exercise and followed the rate ofH⁺ loss from the FV blood for thefirst 30 s of exercise. FV lactate andNa⁺ kinetics differed fromK⁺ kinetics during exercise andrecovery. As predicted from the PCr hydrolysis reaction, the exercisinglimb took up H⁺ and releasedK⁺ at the start of exercise (first30 s) at both exercise intensities, resulting in a FV metabolicalkalosis. K⁺ release wasessentially complete by 3 min, the time at which oxygen uptake (and,presumably, PCr) reached its asymptote. These findings lead us tohypothesize that the early K⁺release by the cell takes place withH⁺ exchange and that the majormechanism for the exercise hyperkalemia is the reduction innondiffusible intracellular anions in the myocyte as PCr hydrolyzes.

     

Stretch-activated ion channels contribute to membrane depolarization after eccentric contractions

We tested the hypothesis that eccentric contractionsactivate mechanosensitive or stretch-activated ion channels (SAC) in skeletal muscles, producing increased cation conductance.Resting membrane potentials and contractile function were measured in rat tibialis anterior muscles after single or multiple exposures to aseries of eccentric contractions. Each exposure produced a significantand prolonged (>24 h) membrane depolarization in exercised musclefibers. The magnitude and duration of the depolarization were relatedto the number of contractions. Membrane depolarization was dueprimarily to an increase in Na⁺ influx, because theestimated Na⁺-to-K⁺ permeability ratio wasincreased in exercised muscles and resting membrane potentials could bepartially repolarized by substituting an impermeant cation forextracellular Na⁺ concentration. Neither theNa⁺/H⁺ antiport inhibitor amiloride nor thefast Na⁺ channel blocker TTX had a significant effect onthe depolarization. In contrast, addition of either of two nonselectiveSAC inhibitors, streptomycin or Gd³⁺, produced significantmembrane repolarization. The results suggest that muscle fibersexperience prolonged depolarization after eccentric contractions due,principally, to the activation of Na⁺-selective SAC.

     

The Involvement of Calcium Ions in Maintenance of Apple Fruit Tissue 9

The hypothesis that the cell walls of apple fruit tissue arebound together by Ca²⁺ ions was tested by infiltration withother cations of similar size. Sr²⁺ and Ba²⁺ were as effectiveas Ca²⁺ in increasing the resistance of apple tissue to failureunder tension while Mg²⁺, Sm³⁺, La³⁺ and Ce³⁺ were less effective.Infiltration with Ca²⁺ increased the tensile strength of tissuefrom air-stored apples to 85% of that of untreated CA-storedfruit. It was concluded that both movement of Ca²⁺ from themiddle lamella and loss of its binding sites occurred duringapple softening, with the movement of Ca²⁺ predominating andthat these processes contribute to changes in tissue structure. Substitution of D₂O for H₂O in infiltration solutions did notaffect the strength of tissue. Key words: Calcium ions, apple fruit, cell walls     

Effects of Some Amino Acid Analogues on the Uptake and Transport of K+ and Ca2+ in Wheat and Mung Bean Seedlings: I. CORTICAL CELL FLUXES AND TRANSPORT TO THE STELE IN EXCISED ROOT SEGMENTS, AS AFFECTED BY p-FLUOROPHENYLALANINE

Effluxes of K⁺ and Ca²⁺ from root segments of both wheat, Triticunaestivum L. cv. Capelle and mung bean, Vigna radiata (L.) Wilczek,were measured in the presence or absence of 20 mol m^–3para-fluorophenylalanine (p-FPA). The results were used to estimatethe compartment contents and transmembrane K⁺ and Ca²⁺ fluxesin root cortex cells. Using the Ussing-Teorell flux equationas the criterion, it was concluded that entry of K⁺ from theoutside solution to the cytoplasm, and from the cytoplasm tothe vacuole were active in both wheat and mung bean. Also, inboth species, Ca²⁺ entered the cytoplasm passively across theplasmalemma and was actively pumped back to the external solution.However, interpretation of the direction of active transportacross the tonoplast depends upon an assumption about Ca²⁺ activityin the cytoplasm. The only qualitative effect of p-FPA was to alter the drivingforce for K⁺ influx, across the plasmalemma in wheat, from anactive to a passive one. Quantitative effects of the analoguewere seen for K⁺ fluxes in both wheat and mung bean and forCa²⁺ fluxes in wheat. The p-FPA reduced transport of K⁺ in bothspecies, while transport of Ca²⁺ was unaffected. The implicationsof these results for the ‘two pump hypothesis’ arediscussed. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis     

Effects of cations on the sugar receptor-site of the blowfly, Phormia

1) Ca^{+ +} (1 to 10 mM) lowered the binding affinity of sugarreceptor-site for sucrose in the labellar sugar receptor ofthe blowfly, Phormia regina, without changing the maximum-responseamplitude. It also elevated the values of the Hill coefficient(n_H) in some degrees. 2) Other divalent cations such as Mg^{+ +}, Ba^{+ +} or Cd^{+ +} alsoshowed almost the same property as above. The sequence of theeffect is as follows: Ba^{+ +}, Mg^{+ +} x Ca^{+ +} x Cd^{+ +}. Trivalentcation, La^{+ + +} (1 mM), changed the value of n_H from 1 (La^{++ +}-free) to 2. 3) On the contrary, the action of monovalent cations such asK⁺ or Na⁺, of which ionic strength was made the same as thatof the divalents hardly suppressed the response. 4) The results obtained do not support the hypothesis, at leaston the sugar receptor of the fly, that the receptor potentialis attributable to a change of the surface potential (zeta potential)as is proposed for the frog sugar receptor.