Changes in the cotyledons of Cucurbita maxima during germination. II. Development of mitochondrial function

Abstract

Mitochondrial respiration in squash cotyledons was followed during germination. Cytochrome oxidase and succinoxidase activities were determined in isolated mitochondrial preparations; tissue localizations of cytochrome oxidase and succinic dehydrogenase were determined histochemically in fresh tissue slices. The respiratory activities differed in light- and dark-germinated plants. In light-grown plants, the respiratory activity reached a peak at 3 days, when the root and the stem were actively growing, and then declined markedly as the tissue became photosynthetic. During the peak, the respiratory activity was present in all the cotyledon tissues; in the foliaceous cotyledons the respiratory activity was localized in the veins. In dark-grown plants the peak of respiratory activity extended over several days and the respiratory rate remained high throughout the cotyledon's life. This broad peak of activity may be related to the mobilization of storage materials for the growth of the embryo axis. In dark-germinated plants, the respiratory activity was widespread throughout the cotyledonary tissues during the peak of activity; the activity became vein localized by 8 days. Electron microscopic studies of cotyledon tissues showed the presence of many mitochondrial profiles in the veinlet regions.