Foraging Efficacy of a Larval Parasitoid in a Cotton Patch: Influence of Chemical Cues and Learning

Plant-herbivore chemical signals and behavioral plasticity may enhance parasitoid host-foraging efficacy in the field; however, no studies have quantified the potential benefits from these factors under field-type conditions. The effect of plant-herbivore signals and learning on the foraging efficacy of Microplitis croceipes was quantified by directly observing and recording total and sequential duration of various foraging behaviors relative to 5 randomly placed herbivore-damaged and host-infested cotton plants and 20 undamaged and non-host-infested plants. Microplitis croceipes spent significantly more time searching (flying and antennation) on host infested versus uninfested plants. Antennation time was significantly and negatively correlated with successive host stings. Contrary to expectations of increased duration, flight time remained constant throughout the foraging bout, which may indicate that there was some learning associated with flight. These results suggest that plant-herbivore chemical signals and learning enhances the foraging efficacy of M. croceipes.     

Proliferation dependence of topoisomerase II mediated drug action

Topoisomerase II mediated DNA scission induced by both a nonintercalating agent [4'-demethylepipodophyllotoxin 4-(4,6-O-ethylidene-beta-D-glucopyranoside) (VP-16)] and an intercalator [4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA)] was studied as a function of proliferation in Chinese hamster ovary (CHO), HeLa, and mouse leukemia L1210 cell lines. Log-phase CHO cells exhibited dose-dependent drug-induced DNA breaks, while plateau cells were found to be resistant to the effects of VP-16 and m-AMSA. Neither decreased viability nor altered drug uptake accounted for the drug resistance of these confluent cells. In contrast to CHO cells, plateau-phase HeLa and L1210 cells remained sensitive to VP-16 and m-AMSA. Recovery of drug sensitivity by plateau-phase CHO cells was found to reach a maximum approximately 18 h after these cells regained exponential growth and was independent of DNA synthesis. DNA strand break frequency correlated with cytotoxicity in CHO cells; log cells demonstrated an inverse log linear relationship between drug dose (or DNA damage) and colony survival, whereas plateau-derived colony survival was virtually unaffected by increasing drug dose. Topoisomerase II activity, whether determined by decatenation of kinetoplast DNA, by cleavage of pBR322 DNA, or by precipitation of the DNA-topoisomerase II complex, was uniformly severalfold greater in log-phase CHO cells compared to plateau-phase cells.     

Calmodulin and troponin C: a comparative study of the interaction of mastoparan and troponin I inhibitory peptide [104-115]

Recent studies using bee and wasp venom peptides have led to the hypothesis that proper complex formation with calmodulin (CaM) requires the presence of a basic amphiphilic helix on the surface of the target protein [Cox, J. A. (1984) Fed. Proc., Fed. Am. Soc. Exp. Biol. 43, 3000]. We have tested this hypothesis by examining CaM and troponin C (TnC) complex formation with two basic peptides, the wasp venom tetradecapeptide mastoparan and the physiologically relevant synthetic troponin I (TnI) inhibitory peptide [104-115], using far-ultraviolet circular dichroism as a secondary structure probe. Complex formation between mastoparan and either CaM or TnC results in an increase in helical content, whereas the helical content of TnI inhibitory peptide does not increase when bound to either protein. Significantly, mastoparan is 78% alpha-helical in a 50% solution of the helix-inducing solvent trifluoroethanol and has a high helix-forming potential according to the Chou-Fasman rules while TnI inhibitory peptide contains none and is not predicted to have any. We interpret these data as indicating that these peptides exhibit substantially different secondary structures upon binding to CaM or TnC. The ability of mastoparan to regulate the acto-subfragment 1-tropomyosin ATPase has also been examined. Mastoparan and TnI inhibitory peptide inhibited 31% and 45% of the activity, respectively. TnC and CaM promote differing degrees of Ca2+-sensitive release of inhibition by both peptides. Sequence comparison suggests that the basic residues present in both peptides are important for binding. However, we conclude that an alpha-helical structure is not a prerequisite for the binding of target proteins to CaM and TnC.     

Interaction of neuroleptic drugs with a synthetic calcium-binding peptide analog of site III of rabbit skeletal troponin C. Phenothiazine selective binding

The effects of nine drugs on the CD spectra of a synthetic calcium binding analog of site III of rabbit skeletal troponin C, can generally be divided into 3 groups: (1) that consisting of haloperidol, benperidol, molindone and promethazine, had no effect on the CD spectrum or calcium sensitivity of the apopeptide; (2) that composed of structurally rigid thioxanthenes, induced CD-detectable structural change in the apopeptide but prevented Ca2+-induced structural change; (3) that consisting of chlorpromazine, trifluoperazine and fluphenazine, induced structural change in the peptide but had no effect on the Ca2+-induced structural change.     

Monovalent ion stimulated adenosine triphosphatase from oat roots

Monovalent ion stimulated ATPase activity from oat (Avena sativa) roots has been found to be associated with various membrane fractions (cell wall, mitochondrial and microsomal) of oat roots. The ATPase requires Mg²⁺ (or Mn⁺²) but is further stimulated by K⁺ and other monovalent ions. The monovalent ions are ineffective in the absence of the divalent activating cation. The ATPase has been described with respect to monovalent ion specificity, temperature, pH, substrate specificity, and Mg²⁺ and K⁺ concentrations. It was further shown that oligomycin inhibits a part of the total ATPase activity and on the basis of the oligomycin sensitivity it appears that at least 2 membrane associated ATPases are being measured. The mitochondrial fraction is most sensitive to oligomycin and the microsomal fraction is least sensitive to oligomycin. The oligomycin insensitive ATPase appears to be stimulated more by K⁺ than the oligomycin sensitive ATPase.     

Effect of cryoprotectant concentration, equilibration time and thawing procedure on survival and development of rapid frozen-thawed mature mouse oocytes

Experiments were conducted to develop a simple rapid-freezing protocol for mature mouse oocytes that would yield a high proportion of oocytes with developmental potential. The effects of concentration (3.5, 4.5 and 6.0 M dimethyl sulfoxide (DMSO) all with 0.5 M sucrose) and the duration of exposure (2.5 min vs 45 sec) of oocytes to the cryoprotectant and its extraction after thawing in 2, 3 or 4 steps of descending sucrose concentration were studied. The most effective of the rapid-freezing and thawing protocols (4.5 M DMSO; 45 sec exposure and 3-step thawing) was compared to slow freezing protocols using 1.5 M DMSO and 1.0 M 1,2 propanediol as cryoprotectants. The DMSO concentrations had an effect on survival, fertilization and embryo development using short (45 sec) but not long (2.5 min) exposure. The rate of morphological oocyte survival was significantly higher using 4.5 M DMSO than 3.5 or 6.0 M (92% vs 82 and 73%, respectively). The development of fertilized embryos to blastocysts was also significantly higher at 4.5 M than at 3.5 or 6.0 M (68% vs 42 and 53%, respectively). The extraction of cryoprotectant in 3 or 4 steps of descending sucrose concentration resulted in higher survival (P < 0.01) and fertilization than in 2 steps. The best survival, fertilization and development was achieved with the 3-step procedure. Optimal combinations of conditions were 4.5 M DMSO at 45 sec prefreeze exposure and 3-step extraction of the cryoprotectant. Oocytes frozen by conventional methods had a survival, fertilization and development to blastocyst rate significantly lower than those frozen under the optimal rapid conditions. Thus rapid freezing of mature mouse oocytes with 4.5 M DMSO + 0.5 M sucrose and short prefreeze exposure is effective and has the additional advantage of being less time-consuming than slow freezing methods.