Behavioral response ofGraminella nigrifrons (Homoptera: Cicadellidae) to experimentally manipulated vibrational signals

Mate recognition for the leafhopper Graminella nigrifrons(Forbes) occurs when a male spontaneously emits a multisectional vibrational calling song to which females respond by emitting simple pulses. Significant differences were found among males in the duration, number of chirps, and chirp rate within sections of the song and the total song. Repeatability (proportion of total variation due to differences among males) of call features ranged from very low (0.04 for total chirps in song) to high (0.67 for section 3 chirp rate). However, song modification and playback experiments revealed that the variation in the measured song features was not important in determining whether a female will respond. Rather, female response depended only on the presence of two of the three types of pulses which comprise a chirp. These essential pulses were found within chirps of all call sections that contain chirps. Manipulation of chirp rates from 0.58 to 2.70 times the normal rate did not affect female response, nor did changing the period of silence between the essential pulse types from 0.25 to 1.75 times the normal period. These results suggest that components of the male calling song function in mate recognition but are not used by females to discriminate among conspecific males.     

Distributional patterns and an additional species of thePassiflora vitifolia complex: Amazonian species diversity due to edaphically differentiated communities

Field studies in Amazonian Peru show that thePassiflora vitifolia complex, a microcosm of many larger taxa, is concentrated in Amazonia with 4 ecologically separated species. One species is restricted to seasonally inundated forests, a second to non-inundated white sand soils, a third to non-inundated lateritic soils, and the fourth mostly to non-inundated alluvial soils. A new combination is formally proposed to recognize the white sand taxon, previously regarded as a variety, as a distinct species:P. involucrata. The importance of -diversity in maintaining high Amazonian species diversity is emphasized.     

Spectroscopic Characterization of Two Soluble Transducers from the Archaeon Halobacterium salinarum

In the present study, structural aspects of the two soluble transducers, HtrX and HtrXI, from the archaeon H. salinarum have been examined using UV circular dichroism and steady-state fluorescence spectroscopies. Circular dichroism (CD) data indicate that both HtrX and HtrXI exhibit salt-dependent protein folding. Under low-ionic-strength conditions (0.2 M NaCl or KCl) the CD spectra of HtrXI is similar to that of the Gdn-HCl- or urea-denatured forms and is indicative of random coil structure. In contrast, the CD spectrum of HtrX under low-ionic-strength conditions contains roughly 85% -helical character, indicating a significant degree of folding. Addition of NaCl or KCl to solutions of HtrX or HtrXI results in CD features consistent with predominately -helical character (>95%) for both proteins. In addition, the transition points (i.e., ionic strengths at which the protein converts from random coil to -helical character) are quite distinct and dependent upon the type of salt present (i.e., either NaCl or KCl). Accessibility of tryptophan residues to the solvent was also examined for both HtrX and HtrXI in both folded and unfolded states using Kl quenching. The Stern–Volmer constants obtained suggest that the tryptophans (Trp35 in HtrX and both Trp47 and Trp74 in HtrXI) are partially exposed to the solvent, indicating that they are located near the surface of the protein in all three cases. Furthermore, fluorescence quenching with the single Trp mutants Trp74AIa and Trp47AIa of HtrXI indicates different environments for these two residues.     

An enclosed-chamber labeling system for the safe <Superscript>14</Superscript>C-enrichment of phytochemicals in plant cell suspension cultures

Summary Various plant secondary products have been implicated in the promotion of good health or the prevention of disease in humans, but little is known about the way they are absorbed in the gut, or in which tissues they are deposited throughout the body. While these issues could be studied if the phytochemicals were isotopically labeled, generating labeled molecules often is problematic because many compounds of interest can be synthesized only in planta at present. In order to generale ¹⁴C-labeled phytochemicals of high radioactive enrichment, we developed an enclosed-chamber labeling system in which cell suspension cultures can be safely and efficiently grown when supplied with ¹⁴C-enriched precursors. The system is designed to hold culture flasks within a clear, polyacrylic compartment that is affixed to the top of a rotary shaker. The flow-through gas exchange nature of the system allows for O₂ replenishment and complete capture of respired ¹⁴CO₂ throughout the entire period of cell culture. Air is circulated internally with the aid of a small fan, and chamber air temperature is monitored continuously with an internal temperature probe and data logger. Production runs of 12–14 d with Vaccinium pahalae (ohelo berry) and Vitis vinifera (grape) suspension cultures, using [¹⁴C]sucrose as the carbon source, demonstrated a 20–23% efficiency of ¹⁴C incorporation into the flavonoid-rich fractions. Further studies with ohelo cell cultures showed that flavonoids were produced with either sucrose or glucose as the carbohydrate source, although flavonoid productivity (measured as anthocyanins) was higher with sucrose. This comprehensive chamber system should have broad applicability with numerous cell types and can be used to generate a wide array of labeled phytochemicals.     

Stability of entomopathogenic bacteria, <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis> and <Emphasis Type="Italic">Photorhabdus luminescens</Emphasis>, during in vitro culture

The entomopathogenic nematode–bacteria complexes Heterorhabditis bacteriophora/Photorhabdus luminescens and Steinernema carpocapsae/Xenorhabdus nematophila are mass produced for use as biological insecticides. Stability of the bacterial partner in culture is essential for maintaining traits important for both biological control and production. Two geographically distinct strains of each bacterial species were isolated from their nematode partners and serially subcultured on in vitro media to assess trait stability. Subculturing resulted in a shift to secondary cell production in one P. luminescens strain and both X. nematophila strains within ten in vitro culture cycles. However, when cell phenotypic variation was controlled in X. nematophila strains by regular selection for primary variants, no trait change was detected in the primary variant after prolonged subculture. When P. luminescens cell phenotypic variation was controlled by selection for primary variants, changes in the primary variant of both strains were noted including reductions in cell and inclusion body size and inclusion body prevalence. Bacterial ability to cause lethal infections following injection into the hemocoel of Tenebrio molitor larvae declined by more than half in primary variants of one P. luminescens strain. Conversely, yield was enhanced, with the subcultured P. luminescens strains showing 53.5 and 75.8% increases in primary cell density. Field adapted traits of primary variant P. luminescens strains tend to deteriorate during in vitro culture as tradeoffs for gains in yield. In vitro producers of the P. luminescens/H. bacteriophora complex must weigh the need for superior bacterial yield against the need to preserve traits important for biological control.     

Comparative effects of trichothecene mycotoxins on bovine platelet function: Acetyl T-2 toxin,a more potent inhibitor than T-2 toxin

The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10^?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.     

Paternal aggression in a biparental mouse: parallels with maternal aggression

Environmental and social factors have important effects on aggressive behaviors. We examined the effect of reproductive experience on aggression in a biparental species of mouse, Peromyscus californicus. Estrogens are important in mediating aggressive behavior so we also examined estrogen receptor expression and c-fos for insights into possible mechanisms of regulation. Parental males were significantly more aggressive than virgin males, but no significant differences in estrogen receptor alpha or beta expression were detected. Patterns of c-fos following aggression tests suggested possible parallels with maternal aggression. Parental males had more c-fos positive cells in the medial amygdala, and medial preoptic area relative to virgin males. The medial preoptic area is generally considered to be relatively less important for male-male aggression in rodents, but is known to have increased activity in the context of maternal aggression. We also demonstrated through habituation-dishabituation tests that parental males show exaggerated investigation responses to chemical cues from a male intruder, suggesting that heightened sensory responses may contribute to increased parental aggression. These data suggest that, in biparental species, reproductive experience leads to the onset of paternal aggression that may be analogous to maternal aggression.     

Enhancement of the rate of pyrophosphate hydrolysis by nonenzymatic catalysts and by inorganic pyrophosphatase

To estimate the proficiency of inorganic pyrophosphatase as a catalyst, ³¹P NMR was used to determine rate constants and thermodynamics of activation for the spontaneous hydrolysis of inorganic pyrophosphate (PP_i) in the presence and absence of Mg²⁺ at elevated temperatures. These values were compared with rate constants and activation parameters determined for the reaction catalyzed by Escherichia coli inorganic pyrophosphatase using isothermal titration calorimetry. At 25 °C and pH 8.5, the hydrolysis of MgPP_i²⁻ proceeds with a rate constant of 2.8 × 10⁻¹⁰ s⁻¹, whereas E. coli pyrophosphatase was found to have a turnover number of 570 s⁻¹ under the same conditions. The resulting rate enhancement (2 × 10¹²-fold) is achieved entirely by reducing the enthalpy of activation (ΔΔH^‡ = −16.6 kcal/mol). The presence of Mg²⁺ ions or the transfer of the substrate from bulk water to dimethyl sulfoxide was found to increase the rate of pyrophosphate hydrolysis by as much as ∼10⁶-fold. Transfer to dimethyl sulfoxide accelerated PP_i hydrolysis by reducing the enthalpy of activation. Mg²⁺ increased the rate of PP_i hydrolysis by both increasing the entropy of activation and reducing the enthalpy of activation.