The Hertz Corporation

About: The Hertz Corporation is a based out in . It is known for research contribution in the topics: Population & Soil water. The organization has 9562 authors who have published 11044 publications receiving 447929 citations. The organization is also known as: Hertz Rental Car & Hertz Rent-a-Car.

An analysis of culmination in Dictyostelium using prestalk and stalk-specific cell autonomous markers.

Abstract: The ecmA (pDd63) and ecmB (pDd56) genes encode extracellular matrix proteins of the slime sheath and stalk tube of Dictyostelium discoideum. Using fusion genes containing the promoter of one or other gene coupled to an immunologically detectable reporter, we previously identified two classes of prestalk cells in the tip of the migrating slug; a central core of pstB cells, which express the ecmB gene, surrounded by pstA cells, which express the ecmA gene. PstB cells lie at the position where stalk tube formation is initiated at culmination and we show that they act as its founders. As culmination proceeds, pstA cells transform into pstB cells by activating the ecmB gene as they enter the stalk tube. The prespore region of the slug contains a population of cells, termed anterior-like cells (ALC), which have the characteristics of prestalk cells. We show that the ecmA and ecmB genes are expressed at a low level in ALC during slug migration and that their expression in these cells is greatly elevated during culmination. Previous observations have shown that ALC sort to surround the prespore cells during culmination (Sternfeld and David, 1982 Devl Biol. 93, 111-118) and we find just such a distribution for pstB cells. We believe that the ecmB protein plays a structural role in the stalk tube and its presence, as a cradle around the spore head, suggests that it may play a further function, perhaps in ensuring integrity of the spore mass during elevation. If this interpretation is correct, then a primary role of anterior-like cells may be to form these structures at culmination. We previously identified a third class of prestalk cells, pstO cells, which lie behind pstA cells in the slug anterior and which appeared to express neither the ecmA nor the ecmB gene. Using B-galactosidase fusion constructs, which give more sensitive detection of gene expression, we now find that these cells express the ecmA gene but at a much lower level than pstA cells. We also show that expression of the ecmA gene becomes uniformly high throughout the prestalk zone when slugs are allowed to migrate in the light. Overhead light favours culmination and it may be that increased expression of the ecmA gene in the pst 'O' region is a preparatory step in the process.

Absence of nitrogen fixation in clover grown on soil subject to long-term contamination with heavy metals is due to survival of only ineffective Rhizobium

Abstract: All strains of Rhizobium isolated from ineffective nodules on white clover (> 50 separate isolations) formed in metal-contaminated soils from a field experiment were demonstrated to be wholly ineffective in nitrogen fixation in plant infection tests on N-free nutrient agar. The plasmid profiles of these isolates were all very similar indicating a lack of genetic diversity in the population surviving in high concentrations of heavy metals. Isolates from comparable field plots of uncontaminated soil had a wide diversity of plasmid profiles. Inoculation of white clover at sowing with a large inoculum of effective Rhizobium leguminosarum bv. trifolii on metal contaminated soil resulted in effective N2-fixation. However, if the inoculated soils were held for 2 months in a moist condition before sowing with white clover, N2-fixation was not detected with inoculum doses of 107 cells pot−1 or less but was obvious where a very large inoculum of 1010 cells pot−1 was added. This indicates that white clover rhizobia are unable to survive (or at least unable to remain effective) in the presence of concentrations of heavy metals close to the current Commission of the European Communities guidelines for environmental protection. A rapid method of assessment of the toxic effects of pollutants on populations of Rhizobium spp is described.

Inhibition of Nitrification in the Activated Sludge Process of Sewage Disposal

Abstract: Summary. A simple method is described for determining the short term effects of sewages, effluents and individual substances on the nitrifying ability of activated sludge and the results of screening many substances are listed. The effects of mixtures of inhibitors and the possibility of formation of complexes between some of those inhibitors were investigated. The long term effects of inhibitors often differ from their immediate effects, one of the most important factors being the ability of activated sludge to become adapted to the inhibitor.

The Factors that Influence Skin Penetration of Solutes

Abstract: In this study, human skin permeation data are analysed using a number of physicochemical descriptors. It is shown that the equilibrium distribution of compounds between the stratum corneum and water (log K m ) can be correlated with either water-octanol partition coefficients (log P oct ) or Abraham solute descriptors. The latter reveals that partitioning of compounds is governed by solute size and hydrogen-bond acidity that favour the stratum corneum, and solute dipolarity/polarizability, and hydrogen-bond basicity that favour water. For water-skin permeation coefficient (log k p ) data it is demonstrated that log P oct cannot be used as a descriptor across a wide range of chemical families, but that log k p can be correlated using Abraham solute descriptors. These disclose that log k p values are increased by solute size and decreased by solute dipolarity/polarizability, hydrogen-bond acidity and hydrogen-bond basicity. It is suggested that different solutes travel through the stratum corneum by the same route, which cannot be distinguished as an intercellular or transcellular mechanism. Backward skin permeation is examined and it is demonstrated that factors governing this process can be rationalized. Furthermore, it is shown that using the Abraham analysis, log P oct can be corrected to correlate log k p over a wide range of compounds. The determination of solute descriptors is also described, indicating that Abraham solute descriptors can be obtained by substructure summation and partition coefficient measurements, so that dermatological properties can be predicted for solutes without the necessity for synthesis