THE PRESENCE AND SIGNIFICANCE OF RESPIRATORY METABOLISM IN STREAK-FORMING CHICK BLASTODERMS

¹ Department of Zoology and Entomology, University of Tennessee, Knoxville, Tennessee

1. Cytochrome oxidase has been detected in chick blastoderms as early as the intermediate-streak stage, by use of the explanting procedure on an agar medium containing dimethyl-p-phenylenediamine-alpha naphthol (nadi reagent). Intracellular indophenol deposition was localized on the surface of lipid droplets, particularly in newly involuted mesodermal cells. Enzymatic activity was negligible in embryos explanted on a similar medium containing sodium azide.

2. Nadi oxidation was augmented, notably in streak mesoderm of early explants after such blastoderms had been starved in saline for a period of five hours. Embryos pretreated in albumen-saline, or albumen-saline-cytochrome c for a similar interval showed no increase or decrease in intracellular enzymatic activity as compared to controls, when they were subsequently explanted onto the nadi-bearing medium. However, diamine oxidation in blastoderms treated in solutions contaming albumen-cytochrome c-hydroquinone and albumen-hydroquinone was perceptibly decreased.

3. The development of the ability to oxidize the nadi reagent was not autonomous in fragments of streak epiblast (prospective mesoderm), but required normal involution at gastrulation. This was shown by pieces of this tissue implanted into trunk-level mesoderm. When implanted in a future head mesoderm location, however, such fragments did reveal an increase in enzymatic activity. When incubated in albumen-saline for intervals of time up to ten hours, small pieces of epiblast did not show an increase in nadi oxidation.

4. These results were correlated with the ability of the tissue fragments to form mesodermal and endodermal structures. Implants of epiblast placed in prospective head mesoderm of streak-forming and definitive primitive streak hosts were incorporated into head mesenchyme and pharyngeal tissue. Similar tissue when placed with other mesoderm at trunk levels failed to differentiate into mesenchyme. Newly involuted mesoderm from streak-forming blastoderms had the same fate as did epiblast fragments, when implanted in a future head mesoderm location. At the trunk level this tissue became integrated into mesoderm cells about it or formed semi-isolated balls of living tissue.

5. The significance of the observations, with respect to nutritional requirements of early chick blastoderms and the relationship between oxygen utilization and differentiation, is discussed briefly.