Monosomy 21: a new case confirmed by in situ hybridization

Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.     

Growth-induced mass flows in fungal networks

Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.     

A single amino acid change in the plant alternative oxidase alters the specificity of organic acid activation.

The alternative oxidase is a quinol oxidase of the respiratory chain of plants and some fungi and protists. Its activity is regulated by redox-sensitive disulphide bond formation between neighbouring subunits and direct interaction with certain alpha-ketoacids. To investigate these regulatory mechanisms, we undertook site-directed mutagenesis of soybean and Arabidopsis alternative oxidase cDNAs, and expressed them in tobacco plants and Escherichia coli, respectively. The homologous C99 and C127 residues of GmAOX3 and AtAOX1a, respectively, were changed to serine. In the plant system, this substitution prevented oxidative inactivation of alternative oxidase and rendered the protein insensitive to pyruvate activation, in agreement with the recent results from other laboratories [Rhoads et al. (1998) J. Biol. Chem. 273, 30750-30756; Vanlerberghe et al. (1998) Plant Cell 10, 1551-1560]. However, the mutated protein is instead activated specifically by succinate. Measurements of AtAOX1a activity in bacterial membranes lacking succinate dehydrogenase confirmed that the stimulation of the mutant protein's activity by succinate did not involve its metabolism. Examples of alternative oxidase proteins with the C to S substitution occur in nature and these oxidases are expected to be activated under most conditions in vivo, with implications for the efficiency of respiration in the tissues which express them.     

Physical microhabitat requirements of freshwater pearl mussels,Margaritifera margaritifera (L.)

Surface sediment diatoms from the east coast of Lake Tanganyika were analysed using ordination and classification techniques, and compared with assemblages previously described from the northern part of the lake. Grain-size analyses were performed on subsamples. Four groups of diatom assemblages were recognised. The first group clusters samples taken in the north, far from the Rusizi river mouth. The second group comprises samples taken on silty sediment along the Tanzanian coast, including one sample taken near the mouth of the Malagarazi river and those from the northernmost part of the lake. The third group comprises surface sediments along the Burundian coast (near Ramba and Magara), and the fourth is characterised by epipsammic taxa. A sample taken near the central arm of the Malagarazi river is included in the latter group. The impact of small rivers on the diatom assemblages in the surface sediments is restricted to the mouth area.     

Use of EDTA to prevent spontaneous cell-to-cell transformation provides a more accurate estimation of gene transfer frequencies

Summary Spontaneous cell-to-cell transformation between naturally competent bacteria on selective media resulted in an overestimation of the transferability of genetic information. EDTA effectively prevented transformation on selective media whereas DNaseI did not reliably inhibit cell-to-cell transformation. An improved method to estimate gene transfer frequencies is described.