Evaluation of Host Suitability in Prunus for Criconemella xenoplax

Methods were developed for screening Prunus selections for host suitability to Criconemella xenoplax. The relative host suitability of selections was based upon a doubling accumulation value (β) that was defined as the number of degree-days (base 9 C) required for doubling of an increment of the initial nematode population. The β value characteristic for C. xenoplax (139 ± 8 degree-days) on suitable hosts was similar to the average β value determined for several peach rootstocks known to be suitable hosts. The β values were 144 ± 21 for Halford, 141 ± 16 for Lovell, and 138 ± 10 for Nemaguard. A higher value for β could indicate poorer host suitability or resistance of a selection to C. xenoplax. All of 369 Prunus accessions tested, including eight accessions that had survived well on a field site infested with C. xenoplax, were suitable hosts. Apparently, resistance to C. xenoplax was not a factor in survival of the accessions planted in the field. Seedlings from P. besseyi, P. pumila ''Mando'', and two interspecific hybrids, Redcoat and Sapalta IR 549-1, failed to support nematode population increase in 44-81% of tests conducted, but all selections supported population increase in some tests. These accessions may have resistance mechanisms that are active only under specific conditions.     

Physical mapping of the MHC and grc by the pulse field electrophoresis

The development of the physical map of the major histocompatibility complex of the rat was undertaken using pulse field gel electrophoresis of fragments of genomic DNA from the BIL/2 (grc ⁺) and BIL/1 (grc ^–) strains obtained primarily from single and double digests with the enzymes Mlu I, Not I, and Sfi I and hybridized with a variety of mouse, rat, and human probes. Both strains are maintained by inbreeding the BIL heterozygote (forced heterozygosity; F31); hence, their differences lie almost entirely in the MHC-grc regions. The MHC-grc region was contained in five fragments of DNA comprising 3000–3200 kilobases (kb); thus, its size appears to be closer to that of the human MHC than to that of the mouse MHC. This didstance may be an underestimate of the size of the entire region, however, because the cluster of class I loci in the RT1.A region could not be defined in detail in this study. The most striking difference between the BIL/2 strain, which has normal growth and reproductive characteristics, and the BIL/1 strain, which has growth and reproductive defects and an enhanced susceptibility to chemical carcinogens, is a deletion of approximately 70 kb in the latter strain. The studies og grc ⁺ and grc ^– strain suggest that the phenotypic defects of the grc ^– stains may be due to the loss of genes that are normally present in this deleted region. Address correspondence and offprint request to: T. J. Gill III.     

Serial Subcultivation of Giardia lamblia in Keister's Modified TYI-S-33 Medium Containing Ultroser G

ABSTRACT. The ability of Giardia strains of the duodenalis type to grow in Keister's modified TYI-S-33 medium varies with serum lot. Recently, strains of Giardia including MR4, WB, and Human-1-Portland, have been cultivated in Keister's modified TYI-S-33 medium containing the serum substitute Ultroser G and have been cultured serially at least 40 times. An optimal concentration of 8% Ultroser G promotes maximal growth in Keister's modified TYI-S-33 medium for all three strains. This concentration of Ultroser G will produce a two-log increase in the number of trophozoites in approximately three days post-inoculation. Generation times for the trophozoites ranging from 6 to 11 h have been achieved in Keister's modified TYI-S-33 containing 10% adult bovine serum and from 8 to 13 h in Keister's modified TYI-S-33 with 8% Ultroser G. Despite the excellent growth of Giardia strains in medium containing Ultroser G, the maximum trophozoite density is only about half of that achieved in Keister's modified TYI-S-33 medium supplemented with 10% adult bovine serum. Comparisons of trophozoites grown with serum or the serum substitute reveal no discernable differences in morphology and motility. Additionally, these strains have been successfully cryopreserved and revived in Keister's modified TYI-S-33 medium supplemented with Ultroser G. Because Ultroser G is a characterized mixture of six main groups of ingredients (growth factors, adhesion factors, mineral trace elements, hormones, binding proteins, and vitamins), the variability in cell proliferation that may occur when changing serum lots should be minimized when using this product.     

Soil ingestion in children: Outdoor soil or indoor dust?

Soil ingestion estimates may play a prominent role in exposure estimation for risk assessments involving tightly bound soil contaminants such as dioxin, PCBs, and lead in soil. Since contamination is often localized to specific areas, the relative contribution of ingested soil due to outdoor soil and indoor dust may have a large impact on the risk assessment. This article examines data on 64 preschool children over 2 weeks to estimate the relative contribution of ingested soil from outdoor soil and indoor dust. Four principal methodological approaches are developed and presented to form the estimates, and their relative strengths and weaknesses are discussed.

The four approaches differ in their assumptions and their ability to detail differences in ingestion source. Two approaches (i.e., duration correlation method — approach 1 and group tracer ratio method — approach 2) were used that can only estimate the average ingestion source, where averages are calculated over subjects and weeks. Both of these approaches have sufficient limitations to preclude confidence in the resulting estimates.

The final two approaches (approach 3 — individual tracer ratio method and approach 4 — multiple statistical model method) were able to characterize ingestion source for individual subject‐weeks and offered more plausible estimates of soil ingestion. Greater emphasis is placed on approach 3 since it was biologically plausible and conceptually straightforward. Approach 3 indicated that 49.2% ± 29.2% of the residual fecal tracers were estimated to be of soil origin. These findings, which represent the first quantitative differentiation of soil vs. dust ingestion, have considerable application for a variety of environmental settings requiring exposure assessment.     

The quantum yield for CO2 uptake in C3 and C4 grasses

The quantum yield for CO₂ uptake was measured in C₃ and C₄ monocot species from several different grassland habitats. When the quantum yield was measured in the presence of 21% O₂ and 340 cm³ m^-3 CO₂, values were very similar in C₃ monocots, C₃ dicots, and C₄ monocots (0.045–0.056 mole CO₂ · mole^-1 quanta absorbed). In the presence of 2% O₂ and 800 cm³ m^-3 CO₂, enhancements of the quantum yield values occurred for the C₃ plants (both monocots and dicots), but not for C₄ monocots. A dependence of the quantum yield on leaf temperature was observed in the C₃ grass, Agropyron smithii, but not in the C₄ grass, Bouteloua gracilis, in 21% O₂ and 340 cm³ m^-3 CO₂. At leaf temperatures between 22–25°C the quantum yield values were approximately equal in the two species.     

An evaluation of the phylogenetic position of the dinoflagellateCrypthecodinium cohnii based on 5S rRNA characterization

Summary Partial nucleotide sequences for the 5S and 5.8S rRNAs from the dinoflagellateCrypthecodinium cohnii have been determined, using a rapid chemical sequencing method, for the purpose of studying dinoflagellate phylogeny. The 5S RNA sequence shows the most homology (75%) with the 5S sequences of higher animals and the least homology (< 60%) with prokaryotic sequences. In addition, it lacks certain residues which are highly conserved in prokaryotic molecules but are generally missing in eukaryotes. These findings suggest a distant relationship between dinoflagellates and the prokaryotes. Using two different sequence alignments and several different methods for selecting an optimum phylogenetic tree for a collection of 5S sequences including higher plants and animals, fungi, and bacteria in addition to theC. cohnii sequence, the dinoflagellate lineage was joined to the tree at the point of the plant-animal divergence, well above the branching point of the fungi. This result is of interest because it implies that the well-documented absence in dinoflagellates of histones and the typical nucleosomal subunit structure of eukaryotic chromatin is the result of secondary loss. and not anindication of an extremely primitive state, as was previously suggested. Computer simulations of 5S RNA evolution have been carried out in order to demonstrate that the above-mentioned phylogenetic placement is not likely to be the result of random sequence convergence.We have also constructed a phylogeny for 5.8S RNA sequences in which plants, animals, fungi and the dinoflagellates are again represented. While the order of branching on this tree is the same as in the 5S tree for the organisms represented, because it lacks prokaryotes, the 5.8S tree cannot be considered a strong independent confirmation of the 5S result. Moreover, 5.8S RNA appears to have experienced very different rates of evolution in different lineages indicating that it may not be the best indicator of evolutionary relationships.We have also considered the existing biological data regarding dinoflagellate evolution in relation to our molecular phylogenetic evidence.     

Mechanism of activation of cyclic GMP-dependent protein kinase from rat liver by multiple modulators

A number of polyanionic compounds, including DNA, RNA and polyglutamate, were shown to exhibit protein kinase stimulatory modulator activity as they were required for cyclic GMP to stimulate the phosphorylation of various cationic substrates by rat liver cyclic GMP-dependent protien kinase. Anionic proteins (casein, phosvitin) were phosphorylated poorly by the enzyme and their phosphorylation was not stimulated by the stimulatory modulators. Studies of the mechanism of action suggest that the modulators interact directly with the substrates to form a complex which is a better substrate than free histone. The observed effect of modulator is complex as it depends on the ratio of modulator to histone and the resultant state of the complex formed (better or poorer substrate than free histone). The observed effect is also dependent on the properties of the histone substrate as Michaelis-Menten kinetics are not observed in the phosphorylation of arginine-rich histone in the absence or presence of cyclic GMP.     

Effect of Estuarine Sediment pH and Oxidation-Reduction Potential on Microbial Hydrocarbon Degradation

Microbial mineralization rates of two petroleum hydrocarbons, as affected by pH and oxidation-reduction potential, were determined in a Barataria Bay, Louisiana, sediment using ¹⁴C-labeled hydrocarbons. Hydrocarbon mineralization rates were inferred from the activity of respired ¹⁴CO₂. Sediment pH and oxidation-reduction potential were important factors in governing the population of hydrocarbon-degrading microorganisms in the sediment and subsequent mineralization rates. Highest mineralization rates occurred at pH 8.0, and the lowest occurred at pH 5.0. At all pH levels mineralization decreased with decreasing oxidation-reduction potential (i.e., increasing sediment anaerobiosis). Generally, mineralization rates for octadecane were greater than those for naphthalene. Aerobic microorganisms in the oxidized sediment were more capable of degrading hydrocarbons than anaerobic microorganisms in reduced sediment of the same pH.