Does the respiratory rate in sea urchin embryos increase during early development without proliferation of mitochondria?

During early development of the sea urchin, the respiratory rate, enhanced upon fertilization, is maintained up to hatching (pre‐hatching period) and then gradually increases to a maximum at the gastrula stage (post‐gastrula period). Except for a short duration after fertilization, respiration in embryos is strongly inhibited by CN− and antimycin A. During the whole span of early development, the amounts of proteins, cytochromes and the specific activities of cytochrome c oxidase and reduced nicotinamide adenine dinucleotide (NADH) cytochrome c reductase in mitochondria are practically the same as in unfertilized eggs. A marked augmentation of mitochondrial respiration after hatching probably occurs without net increase in whole mitochondrial intrinsic capacities. Carbonylcyanide p‐trifluoromethoxyphenylhydrazone (FCCP) or tetramethyl p‐phenylenediamine (TMPD) enhances the respiratory rate in the pre‐hatching period but hardly augments the respiration in the post‐gastrula period. In the presence of both FCCP and TMPD, the respiratory rate in the pre‐hatching period was as high as in the post‐gastrula period. Probably, electron transport in the mitochondrial respiratory chain is regulated by acceptor control and limitation of cytochrome c reduction in the pre‐hatching period and released from those regulations in the post‐gastrula period. Acceptor control of respiration is experimentally reproduced in isolated mitochondria by making adenine nucleotide levels as those levels in the pre‐hatching period.