Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings

The effect of NO₂ fumigation on root N uptake and metabolism was investigated in 3-month-old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO₂ to the plant N budget was measured during a 48 h fumigation with 100mm³m^?3 NO₂. Plants were pre-treated with various nutrient solutions containing NO₂ and NH₄⁺, NO₃^? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH₄⁺ in the solution for 6d led to an increased capacity for NO₃^? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO₃^? uptake. In fumigated plants, NO₂ uptake accounted for 20–40% of NO₃^? uptake. Root NO₃^? uptake in plants supplied with NH₄⁺plus NO₃^? solutions was decreased by NO₂ fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO₂ and NH₄⁺ and were fumigated or not with 100mm³m^?3 NO₂ for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and ¹⁵N labelling. Root NH₄⁺ uptake was approximately three times higher than NO₃^? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO₃^? nor NH₄⁺ accumulated in the shoot, showing that all the absorbed NO₂ was assimilated. Root NO₃^? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO₂-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed.     

Catchment areas in general practice and their relation to size and quality of practice and deprivation: a descriptive study in one London borough.

OBJECTIVE: To relate the sizes of general practice catchment areas in one London borough to list size, deprivation payments, medical staffing, and locally and nationally recognised measures of quality. DESIGN: Study of general practice catchment area maps. SETTING: London borough of Lambeth. SUBJECTS: 60 out of the 71 general practices in Lambeth. MAIN OUTCOME MEASURES: Practice catchment area size with corrections for numbers of doctors and patients. RESULTS: Catchment area size varied greatly between practices, showing an almost 150-fold difference between the largest and smallest practices. This size differential was even more marked when the size of the catchment area was corrected for the number of general practitioners in the practice, where a 300-fold difference was found. Substantial differences existed between practices in each of the four locally assigned quality bands. The weakest practices had catchment areas three times as large as those of the strongest practices. When corrected for medical staffing, the difference was eight times as great. A calculated measure of patient dispersion showed that the practice population of the strongest practices was four times as densely clustered as that of the weakest practices, whose patients were more widely geographically dispersed. CONCLUSIONS: Large variations exist in the size of catchment areas of inner city practices even when corrected for numbers of doctors and patients. These differences are associated with variations in quality of care.     

Dynamic remodeling of the actin cytoskeleton: Lessons learned from Listeria locomotion

The bacterial pathogen Listeria monocytogenes displays the remarkable ability to reorganize the actin cytoskeleton within host cells as a means for promoting cell-to-cell transfer of the pathogen, in a manner that evades humoral immunity. In a series of events commencing with the biosynthesis of the bacterial surface protein ActA, host cell actin and many actin-associated protein self-assemble to from rocket-tail structures that continually grow at sites proximal to the bacterium and depolymerize distally. Widespread interest in the underlying molecular mechanism of Listeria locomotion stems from the likelihood that the dynamic remodeling of the host cell actin cytoskeleton at the cell's leading edge involves mechanistically analogous interactions. Recent advances in our understanding of these fundamental cytoskeletal rearrangements have been achieved through a clearer recognition of the central role of oligo-proline sequence repeats present in ActA, and these findings provide a basis for inferring the role of analogous host cell proteins in the force-producing and position-securing steps in pseudopod and lamellipod formation at the peripheral membrane.     

Localization of Phenolic Compounds in the Covering Tissues of the Embryo of Brassica napus (L.) during Different Stages of Embryogenesis and Seed Maturation

During embryogenesis and maturation of an embryo the tissuescovering it produce phenolic compounds the localization of whichchanges during maturation of the embryo. In the ovary containinga globular embryo, phenolics are located in the epidermis ofthe integumentum externum and the innermost layer of the integumentuminternum. In the ovule at the stage at which heart- and torpedo-shapedembryos are present, phenolic compounds are visible in the stellarcells, the innermost cells of the integumentum internum andthe endosperm. In hard, green seeds, after the integumentuminternum and layers over the stellar cells gradually disappear,the remaining tissue contains cell walls impregnated with phenolics.Mature, black seeds contain only one distinct layer of cells—stellarcells, which, like the other compressed cell walls, are impregnatedwith phenolics. In this way they constitute a barrier betweenthe embryo and its environment.Copyright 1994, 1999 AcademicPress Brassica napus, seed coat, integumentum, phenolic compounds