SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS II. AGROPYRON RIPARIUM X AGROPYRON REPENS

Five hybrids were obtained from 12 seeds formed in 26 emasculated florets of A. riparium pollinated by A. repens. The hybrid plants were morphologically intermediate between the parents for vegetative and spike characteristics, although they resembled A. repens more closely than A. riparium. The 28-chromosome A. riparium parent behaved cytologically as an allotetraploid and formed an average of 13.98 II and 0.04 I in 94 cells at metaphase I. An average of 20.27 II and 0.36 IV were observed at metaphase I in 55 cells of A. repens, which was designated as a segmental autoallohexaploid. The hybrids contained 35 chromosomes and averaged 6.75 I, 12.49 II, 1.05 III, 0.01 IV, and 0.01 V in 162 cells interpreted at metaphase I. Bivalent chromosome pairing in the hybrids was attributed to autosyndetic pairing of 2 A. repens genomes and allosyndetic pairing between 1 A. riparium genome and 1 A. repens genome. Multivalent chromosome associations were attributed to structural hybridity. A. repens and A. riparium apparently share a genome in common, and this genome is the one responsible for rhizomes in both species. A. riparium was given a genome formula of R₂R₂SS; whereas the A. repens genome formula was written as R₁R₁X₁X₁X₂X₂, and the hybrid genome formula was designated as R₁R₂X₁X₂S. The “S” genome of A. riparium was derived from A. spicatum, and the “R” genome is the genome shared by A. repens and A. riparium. The origin and distribution of the so-called “X” genomes of A. repens remain unknown. The hybrids produced from 3 to 10% stainable pollen; however, no seed was set on the hybrids during 2 years in the field.     

Dielectric Spectroscopy: a Rapid Method for the Determination of Solvent Biocompatibility During Biotransformations

Dielectric spectroscopy provides a convenient means of determining the degree of intactness of biological cells. 4-terminal dielectric measurements of suspensions of Saccharomyces cerevisiae at 0.4 MHz show that, as with all other biological cells, these organisms possess a substantial β-dispersion. The additional of octanol to such suspensions causes a rapid decrease in the electrical capacitance of the suspension, which parallels the cellular viability as determined by methylene blue staining. The kinetics of cell death are determined in part by the rate of dissolution of the organic solvent in the aqueous phase. The toxicity of several organic solvents to S. cerevisiae is studied using this technique, and is found to be dependent upon the polarity of the solvent. The present method provides a simple and rapid means for assessing the biocompatibility of solvents used in biotransformations.     

In vitro differentiation of rabbit blastocyst cells

Summary Six- and seven-day post-coitus (p.c.) rabbit embryos have been cultured in an attempt to establish a trophectodermal cell line. Results indicate that cells with epithelial characteristics (i.e. positive staining for cytokeratin) will survive in culture until Passage 3. At that time a fibroblastlike cell becomes predominant. In addition, we have found that the presence of the inner cell mass is required for embryo explants often results in the development of cells that spontaneously contract. These cells stain positively for myosin, which indicates that they may be precardiac cells. Maximum diastolic potential was −59±1.2 mV and the threshold potential was −53±2.3 mV. Spontaneously contracting cells did not respond to atropine, acetylcholine, epinephrine, isoproterenol, or propranolol. Action potential seems to be a result of an inward calcium current, because the beating rate is decreased in a dose-related manner with the calcium channel blocker verapamil, whereas the voltage-sensitive sodium channel blocker tetrodotoxin was without effect. This work was supported by grants HD21302, HD07069, DK31091, and HL37320 from the National Institutes of Health, Bethesda, MD, with additional support from a University of Alabama at Birmingham Cardviovascular Research and Training Center Award.     

Knockdown resistance to dichlorodiphenyl-trichloroethane and pyrethroid insecticides in the napts mutant of Drosophila melanogaster is correlated with reduced neuronal sensitivity

Resistance to pyrethroid insecticides and dichlorodiphenyltrichloroethane (DDT) was investigated in the nap^ts (no action potential, temperature sensitive) mutant of Drosophila melanogaster. In surface contact bioassays, the nap^ts strain showed threefold resistance to deltamethrin at the LC₅₀ level when compared to susceptible Canton-S flies. Cross-resistance was also observed to DDT and the pyrethroids NRDC 157 [3-phenoxybenzyl [1R,cis]-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate], fenfluthrin, and MTI-800 [1-(3-phenoxy-4-fluorophenyl)-4-(4-ethoxyphenyl)-4-methylpentane]. The onset of intoxication by pyrethroids in nap^ts flies was markedly delayed, a finding that is consistent with the existence of a resistance mechanism involving reduced neuronal sensitivity. Resistance at the level of the nerve was confirmed by electrophysiological recordings of spontaneous and evoked activity in the dorsolongitudinal flight muscles of poisoned flies. Preparations from nap^ts insects treated with fenfluthrin displayed longer latencies to the appearance of spontaneous activity and also an absence or reduction in burst discharges compared to equivalent preparations from susceptible individuals. These results are discussed in light of competing hypotheses concerning the mechanism underlying knockdown resistance and reduced nerve sensitivity in insects.