William Jaeckle

Amino Acid Uptake and Metabolism by Larvae of the Marine Worm Urechis caupo (Echiura), a New Species in Axenic Culture

Axenic (bacteria-free) larval cultures of the marine echiuran worm, Urechis caupo, were reliably obtained by aseptically removing gametes directly from the gamete storage organs. Trochophore larvae only removed neutral amino acids from seawater as measured by high-performance liquid chromatography (HPLC). There was no detectable uptake, as measured by HPLC, of acidic or basic amino acids. Kinetic analysis showed that the transport system for alanine in 4-day-old larvae had a Kt of 4-6 µM and a Jmax of 9-10 pmol larva-1 h-1. Following a 50-min exposure, the majority of the radioactivity (95%) from 14C-alanine was found in the trichloroacetic acid-soluble fraction. Very little label appeared as acid-insoluble material, and there was no detectable lipid biosynthesis from 14C-alanine. Approximately 12% of the total alanine transported was released in the form of 14CO2. Thin-layer chromatography of intracellular free amino acid pools demonstrated that aspartic acid and glutamic acid were radiolabeled from the alanine precursor. A comparison of the energy acquired from the transport of alanine, with the metabolic rate of 4-day-old larvae, revealed that 51% of the metabolic demand could be provided by the transport and complete catabolism of this single amino acid at a concentration of 595 nM in seawater.

Corrosion casts: A novel application of a polyurethane resin (PU4ii) for visualizing eggshell pore morphology

ABSTRACT Avian eggshells serve the dual purposes of protecting the developing embryo from the external environment while also facilitating the loss of water vapor and the required exchange of CO2 and O2 gases. Pores that span the eggshell enable the loss of water and trans-shell gas exchange. Although knowledge of the geometry of these spaces is necessary to generate accurate estimates of the rate of gas diffusion across the shell, few techniques exist to obtain these data. Estimates of gas conductance across eggshells are typically calculated from eggshell thickness and the size and number of the pores on the exterior eggshell surface; the trans-shell pore spaces are assumed to be cylindrical in shape. To enable the testing of this assumption, we devised a novel method to visualize the three-dimensional morphology of eggshell pores using PU4ii, a polyurethane-based resin. Casts of the pores of eggshells of the domestic chicken (Gallus gallus) and House Sparrow (Passer domesticus) were unbranched and varied in diameter throughout their length, while casts of the pores of eggshells of the Ostrich (Struthio camelus) revealed a complex network of interconnected spaces. The simplicity of this technique and the stability and resilience of the resulting casts provide opportunities to predict gas flux across the shell and to evaluate the morphology of eggshell pores among birds from different taxonomic groups.