Representation of wild Lactuca spp. (Asteraceae, Lactuceae) in world genebank collections

The spread of the genus Lactuca worldwide includes 16 species in Europe, 51 in Asia, 43 in Africa and 12 in America (mostly North American subcontinent). Natural distributions of Lactuca spp. are compared with the representation of wild Lactuca spp. in world genebank collections as recently summarized in the International Lactuca database (ILDB). A total of 27 wild Lactuca species are reported in world genebank collections in the ILDB, however, due to incorrect taxonomic determination the real number of species is lower. The substantial part (92%) of the collections is represented only by three species (L. serriola, L. saligna, L. virosa) and from a geographic viewpoint they are mostly European in origin. The autochthonous species originating from other continents (Asia, Africa, America), which form c. 83% of known Lactuca spp. richness, are very poorly represented in collections (only c. 3%). The majority of accessions originate from Europe (59%) and Asia (37%), nevertheless the whole area of natural distribution is not well covered. An extremely low number of accessions is available from Africa and America (2% each). Thus, the global biodiversity of Lactuca spp. germplasm is represented very poorly and is biased in genebank collections. For future studies of taxonomy, phytogeography, ecology, phylogenetic relationships, genetic diversity, inter- and intra-population structure, resistance research and practical breeding exploitation of wild Lactuca spp. germplasm, plant material from a wider ecogeographic distribution must be collected and introduced into genebank collections more intensively.     

Endogenous metabolism and macromolecular composition of Arthrobacter globiformis

Arthrobacter globiformis was grown under both carbon- and nitrogen-limiting conditions in a chemostat at a variety of growth rates. Under C-limiting conditions at 25°C, the true growth yield was 602 mg g^?1h^?1 and the specific maintenance rate 0.01 h^?1. However, at dilution rates less than 0.026 h^?1, the energy diverted for maintenance fell. Specific maintenance rates also fell as the growth temperature was lowered to a value of 0.0022 h^?1 at 10°C. The viability of populations at all temperatures remained above 80%. Under N-limiting conditions, viabilities were even higher and cell yields increased markedly as the dilution rate decreased, due to the formation of a glycogen-like reserve material. This made it difficult to calculate a meaningful specific maintenance rate.The chemical composition of the cells depended upon the nature of the medium and the growth rate, with exceptionally high carbohydrate levels, under N-limiting conditions where up to 65% of the cell material was carbohydrate at low growth rates. This accumulation of carbohydrate increased mean cell weights more than four-fold. If C-limited cells were starved, their weight decreased slowly and Q(O₂) rates fell to values close to 1 within a few days. Nitrogen-limited cells when starved lost weight faster due to rapid utilization of the excess carbohydrate. Their viability also decreased and Q(O₂) values only fell to about 3.6 after 28 days.The changes in maintenance requirement and rates of endogenous metabolism are discussed in the context of a fluctuating environment which might be found in soil.     

A packed lysimeter experiment to investigate the effect of surface sealing on hydrology and pesticide loss from the reconstructed profile of a clay soil

Abstract. A laboratory experiment was designed to assess the impact of surface seal development on herbicide loss from a clay soil. The influence of surface sealing on herbicide loss through vertical macropores and lateral throughflow pathways was of particular interest. Losses of the phenylurea herbicide, isoproturon, increased from 0.025% to 0.5% of the total applied under sealed compared with unsealed conditions, as a result of two different mechanisms. First, an increased flow rate through the A horizon under the wetter, sealed conditions resulted in earlier initiation of, and hence a greater volume of, throughflow containing isoproturon in the lysimeters. Second, increased concentrations of isoproturon in macropore and throughflow under the sealed treatments were attributed to the physical and chemical characteristics of the surface seal. Localized reductions in infiltration capacity, changes in soil composition, and decrease in diffusion depth of herbicide within the surface seal are presented as possible mechanisms by which herbicide losses from the sealed soil lysimeters were enhanced.     

Determination of flunixin in edible bovine tissues using liquid chromatography coupled with tandem mass spectrometry

An accurate, reliable, and reproducible assay was developed and validated to determine flunixin in bovine liver, kidney, muscle, and fat. The overall recovery and percent coefficient of variation (%CV) of twenty-eight determinations in each tissue for flunixin free acid were 85.9% (5.9% CV) for liver, 94.6% (9.9% CV) for kidney, 87.4% (4.7% CV) for muscle, and 87.6% (4.4% CV) for fat. The theoretical limit of detection was 0.1 microg/kg (ppb, ng/g) for liver and kidney, and 0.2 ppb for muscle and fat. The theoretical limit of quantitation was 0.3, 0.2, 0.6, and 0.4 ppb for liver, kidney, muscle, and fat, respectively. The validated lower limit of quantitation was 1 ppb for edible tissues with the upper limit of 400 ppb for liver and kidney, 100 ppb for fat, and 40 ppb for muscle. Accuracy, precision, linearity, specificity, ruggedness, and storage stability were demonstrated. Briefly, the method involves an initial acid hydrolysis, followed by pH adjustment ( approximately 9.5) and partitioning with ethyl acetate. A portion of the ethyl acetate extract was purified by solid-phase extraction using a strong cation exchange cartridge. The eluate was then evaporated to dryness, reconstituted, and analyzed using LC/MS/MS. The validated method is sensitive and specific for flunixin in edible bovine tissue.     

Quantitative trait loci for agronomic and seed quality traits in an F2 and F4:6 soybean population

Molecular breeding is becoming more practical as better technology emerges. The use of molecular markers in plant breeding for indirect selection of important traits can favorably impact breeding efficiency. The purpose of this research is to identify quantitative trait loci (QTL) on molecular linkage groups (MLG) which are associated with seed protein concentration, seed oil concentration, seed size, plant height, lodging, and maturity, in a population from a cross between the soybean cultivars ‘Essex’ and ‘Williams.’ DNA was extracted from F₂ generation soybean leaves and amplified via polymerase chain reaction (PCR) using simple sequence repeat (SSR) markers. Markers that were polymorphic between the parents were analyzed against phenotypic trait data from the F₂ and F_4:6 generation. For the F₂ population, significant additive QTL were Satt540 (MLG M, maturity, r² = 0.11; height, r² = 0.04, seed size, r²= 0.06], Satt373 (MLG L, seed size, r² = 0.04; height, r² = 0.14), Satt50 (MLG A1, maturity r² = 0.07), Satt14 (MLG D2, oil, r² = 0.05), and Satt251 (protein r² = 0.03, oil, r² =0.04). Significant dominant QTL for the F₂ population were Satt540 (MLG M,height, r² = 0.04; seed size, r² = 0.06) and Satt14 (MLG D2, oil, r² = 0.05). In the F_4:6 generation significant additive QTL were Satt239 (MLGI, height, r² = 0.02 at Knoxville, TN and r² = 0.03 at Springfield, TN), Satt14 (MLG D2, seed size, r² = 0.14 at Knoxville, TN), Satt373 (MLG L, protein, r² = 0.04 at Knoxville, TN) and Satt251 (MLG B1, lodging r² = 0.04 at Springfield, TN). Averaged over both environments in the F_4:6 generation, significant additive QTL were identified as Satt251 (MLG B1, protein, r² = 0.03), and Satt239 (MLG I, height, r² = 0.03). The results found in this study indicate that selections based solely on these QTL would produce limited gains (based on low r² values). Few QTL were detected to be stable across environments. Further research to identify stable QTL over environments is needed to make marker-assisted approaches more widely adopted by soybean breeders. This revised version was published online in July 2006 with corrections to the Cover Date.