Molecular weights of Cucurbita sieve tube proteins

Summary By means of SDS-polyacrylamide-gel electrophoresis, molecular weights of 15000, 28000, 59000, 116000 and 220000 were determined for the main sieve tube proteins from Cucurbita maxima.     

Some USDA studies on the soybean-Rhizobium symbiosis

Summary The ecology, strain evaluation, genetics of host strain interactions and physiology of nitrogen fixation ofRhizobium japonicum in association with the soybean,Glycine max, were studied. Results of inoculation experiments with selected strains ofRhizobium japonicum indicated that indigenous strains occupied most of the nodules of soybeans grown in highRhizobium japonicum populated soils. Nodule sampling indicated that inoculation did not result in quicker nodulation or a higher incidence of root nodules (primary or secondary) than uninoculated checks. Rhizosphere studies indicated that colonization by introduced strains did occur but did not compete successfully with field strains for nodule sites. Recovery of specific serological types from nodules was influenced by planting intervals. The distribution of the serotypes varied with the time of planting and the age of the plant. Temperature studies indicated that the distribution of serotypes recovered from the nodules was influenced by temperature. Field studies showed the selectivity of soybean genotypes on strains ofRhizobium japonicum. Some strains were more common in the nodules of some varieties than in others. Closely related varieties had similar populations in their nodules. Three genes which control nodule response in soybeans are reported. Nitrogen fixation profiles were determined for some variety-strain interactions. Combinations previously classified as inefficient showed some nitrogenase activity as measured by the acetylene reduction technique. Research Microbiologist; Research Agronomist; Research Plant Physiologist, Soybean Investigations, Crops Research Division, Beltsville, Md. (USDA, ARS); and Plant Pathologist currently located at Michigan State University, East Lansing, Michigan.     

Transduction and Plasmid Deoxyribonucleic Acid Analysis in a Multiply Antibiotic-Resistant Strain of Staphylococcus epidermidis

A genetic analysis of a multiply antibiotic-resistant strain of Staphylococcus epidermidis was performed. Experiments designed to show reversion of organisms to antibiotic susceptibility, as well as studies of the influence of ultraviolet irradiation of phage on the transduction frequencies of the resistance markers, indicated that determinants of chloramphenicol (cml), tetracycline (tet), and neomycin (neo) resistance are present on separate plasmids, but the streptomycin marker is chromosomal. In 2 to 6% of tetracycline-resistant transductants, co-transduction of cml was also observed. By using CsCl-dye density gradients followed by neutral sucrose gradients, the plasmids carrying cml, tet, and neo could be isolated and their molecular weights could be determined. The tetracycline plasmid is shown to be incompatible with one of the cryptic plasmids of a recipient strain.     

Glycol methacrylate embedding in enzyme histochemistry: Application to arthropode tissue incubated for demonstration of unspecific esterase and succinic dehydrogenase activity

Summary The final products of unspecific esterase and succinic dehydrogenase were demonstrated in 1–2 m sections of tick salivary glands embedded in glycol methacrylate (GMA). In the esterase experiments, the tissue specimens were incubated after fixation in glutaraldehyde or acroleïn, and then embedded in GMA. For demonstration of succinic dehydrogenase activity, the specimens were incubated prior to glutaraldehyde fixation followed by embedding in GMA. In sections of all preparations intense enzymatic reaction was observed. High resolution light microscopy could efficiently be used for precise locating of the enzymic products, due to excellent morphologic reference in semithin GMA sections.Supported by the Deutsche Forschungsgemeinschaft. Presented in part at the 4th International Congress on Protozoology, Clermont-Ferrand (France), 2.–9. September 1973.The author was fellow of the Deutsche Forschungsgemeinschaft at the Department of Anatomy, Medical School Hannover, Federal Republic of Germany, during part of this study.