Abstract. Symbiotic DNA sequences involved in nodulation by Rhizobium must include genes responsible for recognizing homologous hosts. We sought these genes by mobilizing the symbiotic plasmid of a broad host-range Rhizobium MPIK3030 (= NGR234) that can nodulate Glycine max, Psophocarpus tetragonolobus, Vigna unguiculata, etc (4), and a number of Rhizobium genes involved in nodule development have been identified. These include genes that are required for synthesis of the enzyme nitrogenase (mf) j as well as some of the nodulation (nod) genes involved in root-hair curling (12, 21), an essential early nodulation step in many legumes (27). Nodulation genes are functionally conserved between R. leguminosarum and R. meliloti (2,11,23), and there is a 69-72% nucleotide sequence homology between the nod ABC genes of these two species (35, 41). In addition, DNA homology is demonstrable between the nod genes of Rhizobium spp and chromosome/plasmid DNAs of most other Rhizobium species (6). This DNA sequence homology between n/f and nod genes of different rhizobia allowed identification of the symbiotic plasmid in the broad-host range Rhizobium spp MPIK3030 (= NGR 234) and localization of the mfand nod gene clusters (1,8,29,33).As speciation within the Rhizobiaceae is defined by hostAbbreviations used in this paper." hsn, rhizobial genes involved in recognition of the host legume; fix, genes required for symbiotic nitrogen fixation; nil a class of fix genes required for synthesis of the enzyme nitrogenase; nod, genes required for nodulation; onc, oncogenic genes (ofAgrobacterium tumefaciens). range, the similarity in nod genes from different Rhizobium species suggests that they are not the sole determinant of hostspecificity. Rather, another set of genes must exist that allow specific rhizobia to recognize certain hosts. Indeed, Kondorosi et al. (21) have identified a region on the R. meliloti sym plasmid, located between nod and nil that appears to be involved in host-specificity. Mutations at this locus could not be complemented by the sym-plasmid from R. leguminosarum (21).In this study we attempted to identify loci on the 460 kbp sym-plasmid of MPIK3030 (MPIK3030 also contains a larger, cryptic plasmid), that contain hsn genes for the hosts Psophcu carpus tetragonolobus, Vigna unguiculata, and related legumes by mobilizing whole plasmids and cosmid-clones of the plasmids into rhizobia that cannot nodulate these hosts. Fully functional, wild-type rhizobia (i.e., can nodulate their homologous hosts) were chosen as the recipients on the assumption that their intact nod genes would be functional on heterologous hosts (2,11,23). Materials and Methods Bacterial StrainsAll strains used are listed in Table I. In general E. coli strains were grown on LB (37), and Rhizobium isolates on TY (3), although Rhizobium sp CB376 was grown on rhizobial minimal medium (in gl-~: mannitol, 10; K2HPO4,

Mercury in the feathers of the Sparrowhawk (Accipiter nisus) from the Erz MountainsThe present paper examines the concentration of mercury in 48 moult-feathers (primaries and secondaries) of the Sparrowhawk from the Erzgebirge region (province of Saxony, Germany). The feathers were collected from 37 females between 1980 and 1998. Five feather-samples of museum-preparations, collected in the area of the federal state of Sachsen before 1930, serve to provide a comparison with times with a low Hg use. All samples were analysed by the Hamburg proton micro-probe. The mercury contents of the moultfeathers from the same bird showed relatively great differences (n = 3 ,,). Only one female showed a clear reduction of the Hg concentration with the progressive moult of the primaries. The feather-samples, collected before 1930, contained 2.7 ppm mercury (n = 5). The concentration increased in the eighties up to 22.6 ppm (n = 25) and decreased to 4.0 ppm in 1997/98. There was a reduction of the amount of mercury entering the environment as a result of human activities after 1990. Regional deviations of contamination were characteristic between the area of the city Chemnitz and the highly contaminated surroundings (1980±1990). The highest mercury concentration was established in the moult-feathers from the region of Niederwiesa-Flo Èha-Falkenau (county Freiberg, 1990). ZusammenfassungIn der vorliegenden Arbeit wird der Quecksilbergehalt von 48 Mauserfedern (Hand-und Armschwingen) des Sperbers aus dem Erzgebirge (Freistaat Sachsen, BRD) untersucht. Die Federn stammen von 37 Weibchen und wurden zwischen 1980 und 1998 gesammelt. Zum Vergleich dienen fu Ènf Federproben von Museumspra Èparaten, die vor 1930 auf dem Gebiet des Freistaates Sachsen gesammelt wurden. Die Federproben wurden mit der Hamburger Protonenmikrosonde analysiert. Die Quecksilbergehalte der Mauserfedern des selben Vogels ko Ènnen relativ groûe Unterschiede aufweisen (n = 3 ,,). Eine deutliche Reduktion der Hg-Konzentration mit fortschreitender Handschwingenmauser zeigte nur ein Weibchen. Als Vergleichswert fu Èr eine Hg-Grundbelastung vor 1930 wurden 2,7 ppm Hg (n = 5) ermittelt. Die in den 1980er Jahren stark angestiegenen Konzentrationswerte (x G = 22,6 ppm, n = 25) fielen 1997/98 auf 4,0 ppm Hg (n = 10) ab, was auf eine Verringerung des anthropogenen Quecksilbereintrages in die Umwelt nach 1990 schlieûen la Èsst. Regionale Kontamina-

The causal agent(s) of dieback of sissoo (Dalbergia sissoo Roxb. ) have not yet been identified unequivocally. Putative microbial pathogens (fungi and bacteria) were studied in dieback affected sissoo trees collected from Bangladesh, using plant pathological techniques combined with molecular tools. DNA based characterization showed the presence of heterogeneous patterns of various fungi (mostly saprophytic). It did not support the hypothesis of Fusarium solani being the cause of sissoo dieback. In contrast, isolation and molecular characterisation of bacteria from dieback affected sissoo revealed the presence of Pseudomonas in 83% of the samples. Sequencing the gene of 16S ribosomal RNA, the rpoD-gene, the gacAgene and the rnpB-gene strongly suggested that these isolates belong most probably to a still unassigned Pseudomonas species. Hypersensitivity response assays and infection studies using sissoo seedlings demonstrated their pathogenic potential.

Summary Mercury in the feathers of the Sparrowhawk (Accipiter nisus) from the Erz Mountains The present paper examines the concentration of mercury in 48 moult‐feathers (primaries and secondaries) of the Sparrowhawk from the Erzgebirge region (province of Saxony, Germany). The feathers were collected from 37 females between 1980 and 1998. Five feather‐samples of museum‐preparations, collected in the area of the federal state of Sachsen before 1930, serve to provide a comparison with times with a low Hg use. All samples were analysed by the Hamburg proton micro‐probe. The mercury contents of the moult‐feathers from the same bird showed relatively great differences (n = 3 ♀♀). Only one female showed a clear reduction of the Hg concentration with the progressive moult of the primaries. The feather‐samples, collected before 1930, contained 2.7 ppm mercury (n = 5). The concentration increased in the eighties up to 22.6 ppm (n = 25) and decreased to 4.0 ppm in 1997/98. There was a reduction of the amount of mercury entering the environment as a result of human activities after 1990. Regional deviations of contamination were characteristic between the area of the city Chemnitz and the highly contaminated surroundings (1980 – 1990). The highest mercury concentration was established in the moult‐feathers from the region of Niederwiesa‐Flöha‐Falkenau (county Freiberg, 1990).

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