Studies on controlled and released respiration in animal and vegetal halves of the embryo of the sea urchin, Paracentrotus lividus

Abstract

Summary Eggs of the sea urchin Paracentrotus lividus were separated in the 16–32 cell stage in animal and vegetal halves. These were allowed to develop, and the respiration of the halves was measured in the microrespirometer of Linderstrom-Lang and Holter. The measurements referred to advanced cleavage stages (≥128 cells) and to the mesenchyme blastula stage or beginning gastrula stage. The medium was either pure sea water or sea water within the addition of 5×10 −5 M 2,4-dinitrophenol. In the first medium the “controlled” in the latter the “released” respiration was measured. A survey of the results is given in Figs. 1 and 2. In both stages which were subject to examination, the respiratory control ratios (released respiration over controlled respiration) in animal halves were high, about 2.9, a value corresponding to that found immediately after fertilization in whole eggs suspended in normal sea water [14]. In advanced cleavage stage, the respiratory rate seemed to be higher in vegetal than in animal halves. Addition of dinitrophenol caused a certain decrease in the respiratory rate (Fig. 1). Vegetal halves in the mesenchyme blastula state (Fig. 2), on the other hand, showed a respiratory rate not significantly different from that in animal halves. Upon addition of dinitrophenol only a rather low increase in the respiratory rate occurred (Fig. 2). Controls were made in order to ascertain that the changes in respiratory rate were not due to damage caused by the process of separating the halves. As the released respiration expresses the maximal electron transport capacity [24], it may also be considered an approximate measure of the amount of respiratory enzyme chains present in the embryos. Thus, a considerable synthesis of these enzymes must take place in the isolated animal halves. This is in agreement with the increasing incorporation of amino acids in isolated animal halves, demonstrated by Markman [21]. The results with isolated vegetal halves at mesenchyme blastula stage indicate, on the other hand, that the amount of respiratory enzyme chains is lower than in animal halves, which again corresponds to studies on incorporation of labeled amino acids [21]. The different values of the respiratory control ratio in animal and vegetal halves indicate differences in metabolic state. A high value of the ratio is in keeping with an accumulation of energy-rich compounds, whereas lower values indicate that a certain steady state has been approached. The interactions between animal and vegetal regions which display themselves in the normal development are discussed in the light of the results obtained. Financial support was given from the Swedish Natural Sciences Research Council, the Swedish Cancer Society and the Consiglio Nazionale delle Recerche (Rome). These grants are most gratefully acknowledged.