Retention and mobility of atmospheric particle-associated organic pollutant PCDD/Fs and PAHs in maize leaves

The fate of polychlorinated dibenzo- p -dioxins and dibenzofurans and polycyclic aromatic hydrocarbons deposited to maize leaves under ambient conditions was investigated, with focus on those compounds that are primarily associated with particles in the atmosphere. Leaf samples collected from mature maize plants over an 8-wk period were subjected to four extraction procedures: (1) rinsing with distilled water; (2) shaking in aqueous EDTA solution; (3) immersion in chloroform/methanol; (4) soxhlet extraction with toluene. Of the compounds deposited primarily in association with particles, > 20% of the total leaf contamination was present in the first two aqueous extracts, indicating that only a small portion of these substances was subject to ready erosion from the leaf surfaces. Some 50–60% of the chemical was present in the third extract, while 20–40% was found in the final extract. The chemical in the final extract was no longer associated with particles, since these had been removed with the first three extractions. This chemical must have desorbed from the particles with which it was originally deposited, and migrated through the epicuticular waxes. Model calculations indicated that 15–35% of the chemical in the third extract had also desorbed from the particles, and there was evidence that polychlorinated dibenzo- p -dioxins and dibenzofurans desorb more readily than polycyclic aromatic hydrocarbons. It is concluded that desorption of chemical from particles and subsequent transport through the cuticle is an important process determining plant accumulation of organic contaminants associated with atmospheric particles.     

ANATOMY OF PSEUDOTRITONIA THIELE, 1912 AND NOTAEOLIDIA ELIOT, 1905 (GASTROPODA: OPISTHOBRANCHIA: NUDIBRANCHIA) FROM SIGNY ISLAND, ANTARCTICA

Several species of nudibranch molluscs are abundant amongstthe rich benthic hard substratum communities found close tothe British Antarctic Survey base at Signy Island, in the Atlanticsector of the Antarctic. Over the austral summer 1992/1993,two of the authors (LWB and DKAB) were able to collect someof the lesser known species of Nudibranchia at depths between3 and 40 metres, using SCUBA. New information on morphologyand anatomy of two of these species, Pseudotritonia gracilidensOdhner, 1944 (Charcotiidae, Arminoidea) and Notaeolidia gigasEliot, 1905(Notaeolidiidae, Aeolidoidea) are presented in thispaper. The validity of the species Notaeolidia gigas is strengthened. (Received 9 February 1994; accepted 18 September 1994)     

Keratin Polypeptide Analysis in Fetal and in Terminally Differentiating Newborn Mouse Epidermis

The keratin polypeptide pattern of neonatal mouse epidermis consists of eight individual polypeptides having molecular weights of between 46,000 and 67,000. Unlike the keratin patterns in adult mouse epidermis, this pattern is not subject to body site-specific alterations regarding the specific content of distinct polypeptides or the absolute number of keratin constituents.
At day 16 of fetal development the neonatal keratin pattern is only partially expressed, it being fully completed just prior to birth at day 19 of gestation. A comparative analysis of the sequential changes in epidermal morphology and keratin pattern during the last third of embryonic development confirms the view that, independent of the species, keratin polypeptides below 60,000 mol. wt. are generated by basal cells, whereas the biosynthesis of high molecular weight keratin members take place in the suprabasal cell compartments of keratinizing epithelia. The site of origin of five polypeptides (60,000, 58,000, 52,000, 49,000, 46,000) could therefore be attributed to the basal cell layer, the remaining three polypeptides (67,000, 64,000, 62,000) being synthesized in the outer metabolically active epidermal layers. Similar conclusions could be drawn after subfractionation of neonatal epidermis into living (basal, spinous, and granular) and dead cell layers (stratum corneum), and investigation of the corresponding keratin patterns.
During their progression through the epidermis, two proteins (60,000, 58,000) undergo a hitherto undescribed type of posttranslational modification characterized by a slight increase in size and a change in electrical charge. The mechanism underlying this modification is unknown and it is unclear whether the modification if functional or trivial. The largest keratin polypeptide (67,000) of the protein family - probably a product of spinous cells - disappears from the cornified layer without any evidence that it serves as a precursor for smaller keratin subunits.     

Molecular and morphological data reveal cryptic taxonomic diversity in the terrestrial slug complex Arion subfuscus/fuscus (Mollusca, Pulmonata, Arionidae) in continental north-west Europe

The importance and abundance of cryptic species among invertebrate taxa is well documented. Nowadays, taxonomic, phylogenetic and conservation biological studies frequently use molecular markers to delineate cryptic taxa. Such studies, however, often face the problem of the differential resolution of the molecular markers and techniques involved. This issue is explored in the present study of cryptic taxa within the terrestrial slug complex Arion subfuscus/fuscus in continental north-west Europe. To this end, morphological, allozyme and mitochondrial 16S rDNA sequence data have been jointly evaluated. Using allozyme data and gonad type, two distinct groups were consistently delineated, even under sympatric conditions. The 16S rDNA data strongly supported both those groups and even suggested the presence of three distinct taxa within one of them. However, in view of: (1) the allopatric distribution of three OTUs, (2) the lack of allozyme or morphological differentiation, and (3) the extremely high degree of intraspecific mtDNA variation reported in pulmonate gastropods, they are, for the time being, not regarded as valid species under the biological species concept. By means of 16S rDNA and allozyme data, the position of type and topotype material of A. subfuscus s.s. and A. fuscus relative to the newly defined OTUs was determined, thus clarifying the nomenclature of this species complex. Additionally, gonad type proved to be a useful character for distinguishing the two species in north-west Europe.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 23–38.     

Effects of elevated CO2 concentrations on photosynthesis, growth and reproduction of branches of the tropical canopy tree species, Luehea seemannii Tr. & Planch.

Mature trees have already experienced substantial increases in CO₂ concentrations during their lifetimes, and will experience continuing increases in the future. Small open-top chambers were used to enclose branchlets that were at a height of between 20 and 25 m in the canopy of the tree species Luehea seemannii Tr. & Planch. in a tropical forest in Panamá. Elevated concentrations of CO₂ increased the rate of photosynthetic carbon fixation and decreased stomatal conductance of leaves, but did not influence the growth of leaf area per chamber, the production of flower buds and fruit nor the concentration of nonstructural carbohydrates within leaves. The production of flower buds was highly correlated with the leaf area produced in the second flush of leaves, indicating that the branchlets of mature trees of Luehea seemannii are autonomous to a considerable extent. Elevated levels of CO₂ did increase the concentration of nonstructural carbohydrates in woody stem tissue. Elevated CO₂ concentration also they increased the ratio of leaf area to total biomass of branchlets, and tended to reduce individual fruit weight. These data suggest that the biomass allocation patterns of mature trees may change under future elevated levels of CO₂. Although there were no effects on growth during the experiment, the possibility of increased growth in the season following CO₂ enrichment due to increased carbohydrate concentrations in woody tissue cannot be excluded.