Characterization of transgenic poplar with ectopic expression of pine cytosolic glutamine synthetase under conditions of varying nitrogen availability

The present study addresses the hypothesis that enhanced expression of glutamine synthetase (GS) in transgenic poplar, characterized by the ectopic expression of pine cytosolic GS, results in an enhanced efficiency of nitrogen (N) assimilation and enhanced growth. Transgenic and control poplar were supplied with low and high N levels and the role of ectopic expression of the pine GS in growth and N assimilation was assessed by using amino acid analysis, (15)N enrichment, biochemical analyses, and growth measurements. While leaves of transgenic poplar contained 85% less (P < 0.01) free ammonium than leaves of nontransgenic control plants, leaves of transgenics showed increases in the levels of free glutamine and total free amino acids. Transgenic poplar lines also displayed significant increases in growth parameters when compared with controls grown under both low (0.3 mm) and high (10 mm) nitrate conditions. Furthermore, (15)N-enrichment experiments showed that 27% more (P < 0.05) (15)N was incorporated into structural compounds in transgenic lines than in nontransgenic controls. Using the methods described here, we present direct evidence for increased N assimilation efficiency and growth in GS transgenic lines.     

Influence of Forest Management on the Species Richness and Composition of Wood-inhabiting Basidiomycetes in Swiss Forests

In order to investigate the diversity of wood-inhabiting aphyllophoroid basidiomycetes in Swiss forests, 86 plots of 50 m ² were established. They harboured a total of 3339 samples of woody debris, classified according to three categories (coarse, fine, and very fine woody debris), yielding 238 species of wood-inhabiting fungi. The selected sites cover the main forest types of Switzerland and various degrees of management intensity. A multiple linear regression analysis showed that substrate variation, i.e. differences in the quality of dead wood, including volume, age, degree of decomposition and host tree species, are the most important factors influencing diversity of wood-inhabiting fungi. In addition, a Principle Coordinate Analysis highlighted differences in the fungal communities in the different forest types. The greatest fungal species richness is found on thermophilic deciduous tree and woody shrub species. Fine and very fine woody debris, even present in intensively managed forests, often serve as important refuges for many species. Forests with a recent management intervention were found to be either species poor or species rich. Possible reasons for these differences may lay in forest size and landscape fragmentation, the distance to the nearest species pool or microclimatic factors. In Switzerland intensively managed forests harbour significantly less wood-inhabiting, aphyllophoroid fungi than non-managed or extensively managed forests. This is the case in both deciduous forests and in conifer forests. However, occasionally intensively managed forest will also harbour rare and endangered species.     

Tissue-specific localization of gibberellins and expression of gibberellin-biosynthetic and signaling genes in wood-forming tissues in aspen

Bioactive gibberellins (GAs) are known regulators of shoot growth and development in plants. In an attempt to identify where GAs are formed, we have analyzed the expression patterns of six GA biosynthesis genes and two genes with predicted roles in GA signaling and responses in relation to measured levels of GAs. The analysis was based on tangential sections, giving tissue-specific resolution across the cambial region of aspen trees (Populus tremula). Gibberellin quantification by GC/MS-SRM showed that the bioactive GA1 and GA4 were predominantly located in the zone of expansion of xylem cells. Based on co-localization of the expression of the late GA biosynthesis gene GA 20-oxidase 1 and bioactive GAs, we suggest that de novo GA biosynthesis occurs in the expanding xylem. However, expression levels of the first committed GA biosynthesis enzyme, ent-copalyl diphosphate synthase, were high in the phloem, suggesting that a GA precursor(s) may be transported to the xylem. The expression of the GA signaling and response genes DELLA-like1 and GIP-like1 coincided well with sites of high bioactive GA levels. We therefore suggest that the main role of GA during wood formation is to regulate early stages of xylem differentiation, including cell elongation.     

Volume interpolation of CT images from tree trunks

Computerized tomography as a non-destructive scanning method to analyze wood structures has become an important technique in tree research. The possibility to reconstruct three-dimensional volumes based on a number of slices of two-dimensional data from CT scans is strongly dependent on the number of measured slices. Radial basis function methods can be successfully used to interpolate CT images with the aim of obtaining a satisfactory reconstruction of tree trunks. In contrast to standard interpolation techniques, our method takes into account that wood structures differ more in the radial than in the longitudinal direction. Therefore we obtain better interpolation results for wood structures.     

Factors influencing in vitro infectivity and growth of Rickettsia peacockii (Rickettsiales: Rickettsiaceae), an endosymbiont of the Rocky Mountain wood tick, Dermacentor andersoni (Acari, Ixodidae)

Rickettsia peacockii, a spotted fever group rickettsia, is a transovarially transmitted endosymbiont of Rocky Mountain wood ticks, Dermacentor andersoni. This rickettsia, formerly known as the East Side Agent and restricted to female ticks, was detected in a chronically infected embryonic cell line, DAE100, from D. andersoni. We examined infectivity, ability to induce cytopathic effect (CPE) and host cell specificity of R. peacockii using cultured arthropod and mammalian cells. Aposymbiotic DAE100 cells were obtained using oxytetracycline or incubation at 37 degrees C. Uninfected DAE100 sublines grew faster than the parent line, indicating R. peacockii regulation of host cell growth. Nevertheless, DAE100 cellular defenses exerted partial control over R. peacockii growth. Rickettsiae existed free in the cytosol of DAE100 cells or within autophagolysosomes. Exocytosed rickettsiae accumulated in the medium and were occasionally contained within host membranes. R. peacockii multiplied in other cell lines from the hard ticks D. andersoni, Dermacentor albipictus, Ixodes scapularis, and Ixodes ricinus; the soft tick Carios capensis; and the lepidopteran Trichoplusia ni. Lines from the tick Amblyomma americanum, the mosquito Aedes albopictus, and two mammalian cell lines were non-permissive to R. peacockii. High cell densities facilitated rickettsial spread within permissive cell cultures, and an inoculum of one infected to nine uninfected cells resulted in the greatest yield of infected tick cells. Cell-free R. peacockii also were infectious for tick cells and centrifugation onto cell layers enhanced infectivity approximately 100-fold. The ability of R. peacockii to cause mild CPE suggests that its pathogenicity is not completely muted. An analysis of R. peacockii-cell interactions in comparison to pathogenic rickettsiae will provide insights into host cell colonization mechanisms.     

Survival and escape of Agrobacterium tumefaciens in triploid hybrid lines of Chinese white poplar transformed with two insect-resistant genes

Two partly modified insect-resistant genes (BtCryI Ac gene [Bt gene toxin against Lepidopterean insects] and API gene [arrowhead proteinase inhibitor]) were transferred to the triploid hybrid of Chinese white poplar ((Populus tomentosa Carr. × Populus bolleana Louche) × Populus tomentosa Carr.) mediated by A. tumefaciens. The survival of Agrobacterium in transgenic plants was examined during the processes of transplanting and subculturing on the nutrient medium. The results suggested that 80% of the plants, which were obtained by repeated selection on media added with 50 mg/L kanamycin and 300 mg/l carbenicillin, showed positive reactions after examination using molecular methods. The ELISA test indicated that the Bt toxoprotein was expressed in seven of the transgenic sub-clones. Leaves, stems, and roots of all the 28 transgenic plants were cultured on the YEB medium added with 50 mg/L kanamycin, and it was found that Agrobacterium survived in three sub-clones (33, 37, 5) and could have existed for 24 months in the bottle. These three transgenic sub-clones were transplanted and cultivated for one month in the room, and then the target Agrobacterium was found in rhizosphere of the sub-clone 33.     

Metal Transport and Bioavailability in Soil Contaminated with CCA-Treated Wood Leachates

A laboratory study was conducted to investigate metal transport and accumulation within soils contaminated with As, Cr, and Cu from CCA-treated wood leachates. New blocks of CCA-treated wood were leached using synthetic rainwater. Soil columns were constructed and filled with three different soils, including a sandy soil, an organic soil and a clay soil. The leachate was applied intermittently until 80 pore volumes were eluted through each column. Metal concentrations (Cu, Cr, and As) were measured in the leachate before passage through the columns as well as in each elutriate fraction collected. Chemical analysis was complemented with toxicity testing using Ceriodaphnia dubia, Selenastrum capricornutum, and MetPLATE?. Following application of 80 pore volumes of leachate, the columns were dissected and the profile of the metal concentrations within each column was determined. A comparison of the arsenic, chromium and copper leaching patterns found arsenic to be the most mobile, with copper the most retained in the soil columns (As < Cr < Cu). Transport patterns of As differed in the three soil types, with observed mobility highest in the sandy soil and lowest in the clay soil. The three metals accumulated in the top layer of soil. Arsenic posed the greatest risk when soil concentrations were compared to risk-based target levels. Although metals were detected in soil elutriates, no toxicity was detected in any of the soil column elutriates using any of the three toxicity assays.     

First record of Cercidiphylloxylon(Cercidiphyllaceae)from the Palaeocene of Fushun,NE China

Cercidiphylloxylon spenceri(Brett)Pearson is described from the Lizigou Formation,Palaeocene in China.The growth rings are distinct; pores are diffuse,solitary,with somewhat angular outlines in cross section;vessel elements long with long scalariform perforation plates; intervessel pitting is opposite to scalariform; fibertracheids are present; axial parenchyma is scarce; rays are mostly biseriate and heterogeneous.All wood characters of the fossil specimen fall into the range of those of extant Cercidiphyllum(Cercidiphyllaceae).The finding is one of the earliest fossil wood records of Cercidiphyllaceae.