Evolution in an autopolyploid group displaying predominantly bivalent pairing at meiosis: genomic similarity of diploid Vaccinium darrowi and autotetraploid V. corymbosum (Ericaceae).

The genomic relationship between V. darrowi Camp (2n = 2x = 24) and V. corymbosum L. (2n = 4x = 48) was examined using an interspecific tetraploid hybrid, US 75, and representatives of the parental species. Two features in the background of US 75 led to the prediction that it was an allopolyploid: (1) the parental species are quite distinct morphologically and geographically, and (2) the diploid genome was incorporated into US 75 via an unreduced gamete. However, US 75 recently was shown to display tetrasomic inheritance using molecular markers. In the present cytological study, US 75 was found to have a lower than expected number of multivalents for an autopolyploid, although it had a significantly higher number of quadrivalents than its autotetraploid parent, V. corymbosum. Normal chromosome distributions were observed at anaphase I and II, and pollen viability was high. Our findings suggest that little genomic divergence has developed between the Vaccinium species and that the polyploids may freely exchange genes with sympatric diploid species via unreduced gametes. This pattern of hybridization could be an important component of evolution in all autopolyploid groups, making them much more dynamic than traditionally assumed.

Channel structures in aerobic biofilms of fixed-film reactors treating contaminated groundwater.

Scanning electron microscopy, confocal scanning laser microscopy, and fatty acid methyl ester profiles were used to study the development, organization, and structure of aerobic multispecies biofilm communities in granular activated-carbon (GAC) fluidized-bed reactors treating petroleum-contaminated groundwaters. The sequential development of biofilm structure was studied in a laboratory reactor fed toluene-amended groundwater and colonized by the indigenous aquifer populations. During the early stages of colonization, microcolonies were observed primarily in crevices and other regions sheltered from hydraulic shear forces. Eventually, these microcolonies grew over the entire surface of the GAC. This growth led to the development of discrete discontinuous multilayer biofilm structures. Cell-free channel-like structures of variable sizes were observed to interconnect the surface film with the deep inner layers. These interconnections appeared to increase the biological surface area per unit volume ratio, which may facilitate transport of substrates into and waste products out of deep regions of the biofilm at rates greater than possible by diffusion alone. These architectural features were also observed in biofilms from four field-scale GAC reactors that were in commercial operation treating petroleum-contaminated groundwaters. These shared features suggest that formation of cell-free channel structures and their maintenance may be a general microbial strategy to deal with the problem of limiting diffusive transport in thick biofilms typical of fluidized-bed reactors.

Reflection confocal imaging of type I and type III isozymes of hexokinase in PC12 cells.

Reflection confocal microscopy was used to determine the intracellular distribution of Type I and III isozymes of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) in PC12 cells; detection was by staining with diaminobenzidine as a substrate for horseradish peroxidase-conjugated antimouse immunoglobulins bound to isozyme-specific monoclonal antibodies. With both isozymes, detection of the staining pattern was significantly enhanced by reflection confocal imaging compared with viewing with transmitted brightfield optics. For Type I, prominent staining of cytoplasmic organelles having a distribution consistent with that of mitochondria was noted. For Type III, intense staining at the nuclear periphery was observed. A distinct punctate pattern along the nuclear surface implied a nonuniform distribution of the Type III hexokinase and may represent preferential association with nuclear pore structures. A study of technical factors involved in optimizing the reflection image was conducted. We demonstrate that both the choice of objective and the thickness of the mounting medium are critical to successful imaging, and we describe a simple test for assessing the suitability of objectives in any system.