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.     

Selective loss of uncoupling protein mRNA in brown adipose tissue on deacclimation of cold-acclimated mice

The time course of changes in the level of uncoupling protein mRNA when cold-acclimated mice were returned to a thermoneutral environment (33 degrees C) was examined using a cDNA probe. Upon deacclimation, there was a marked loss of uncoupling protein mRNA within 24 h, which precedes the loss of uncoupling protein from mitochondria. This loss of uncoupling protein mRNA was selective, since there was no change in the relative proportion of cytochrome c oxidase subunit IV mRNA or poly(A)+ RNA in total RNA. The results suggest that the decrease in the mitochondrial content of uncoupling protein during deacclimation is likely the result of turnover of existing protein, with very little replacement due to a lower level of its mRNA.     

Superoxide perturbation of the organization of vascular endothelial cell membranes

Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose.     

Regulation of enterochelin synthetase in Escherichia coli K-12

Enterochelin synthetase activity is controlled by both repression and feed-back inhibition mechanisms. Inclusion of iron in growth media results in synthesis of all four (D, E, F and G) components of enterochelin synthetase being repressed. The specific inhibition of L-serine activation (partial reaction catalyzed by the F component) by the end products, ferric-enterochelin and 2,3-dihydroxybenzoylserine, is shown to inhibit overall enterochelin synthetase activity.