Attenuation of Symbiotic Effectiveness by Rhizobium meliloti SAF22 Related to the Presence of a Cryptic Plasmid.

Several wild-type strains of Rhizobium meliloti isolated from alfalfa nodules exhibited different plasmid profiles, yet did not differ in growth rate in yeast-mannitol medium, utilization of 43 different carbon sources, intrinsic resistance to 14 antibiotics, or detection of 16 enzyme activities. In contrast, three measures of effectiveness in symbiotic nitrogen fixation with alfalfa (shoot length, dry weight, and nitrogen content) indicated that R. meliloti SAF22, whose plasmid profile differs from those of the other strains tested, is significantly less effective than other wild-type strains in symbiotic nitrogen fixation. Light microscopy of nodules infected with strain SAF22 showed an abnormal center of nitrogen fixation zone III, with bacteria occupying a smaller portion of the infected host cells and vacuoles occupying a significantly larger portion of adjacent uninfected host cells. In contrast, the effective nodules infected with other wild types or plasmid pRmSAF22c-cured segregants of SAF22 did not display this cytological abnormality.

Application of the quadratic response surface in the polarographic determination of lead: biological samples.

Differential-pulse polarography was applied to lead determination in blood, urine and hair samples after pressurized acid digestion. Quantitative determination was carried out using a single analytical measurement of the experimental sample (without the need for addition or calibration methods), using the equation calculated as a result of the study of the quadratic response surface. The elimination of the possible interferences has been considered. The reliability of the analytical procedure was evaluated using relative standard deviations (2.34-11.93%) and recovery (97.28-103.92%) measurements.

Direct determination of zinc in insulin preparations by differential pulse polarography.

A rapid and direct differential pulse polarographic method for the determination of zine in insulin preparations is described. Optimum conditions were studied using 0.2 M acetate buffer (pH 4.1) as the supporting electrolyte. Agreement between the results by direct analysis and those by the procedure involving pressurized digestion was satisfactory.