Ultrastructural analysis of cytochrome oxidase in chick epiphyseal growth plate cartilage

Histochemical detection of cytochrome oxidase activity in chicken growth plate revealed both positively and negatively stained mitochondria in chondrocytes of all zones, i.e., proliferative, pre-hypertrophic, hypertrophic, and calcifying zones. The proportion of positive to negative cells was lowest in the proliferative zone. As cytodifferentiation progressed, more positively stained cells were present. In positive cells all mitochondria were usually stained, and in negative cells all mitochondria were unstained. A few cells appeared to be in transition and contained both types of mitochondria. The results indicate that chondrocytes utilizing both aerobic and anaerobic metabolism are present in growth plate cartilage and that oxidative metabolism is favored in the more mature cells. The relationship of oxidative metabolism to calcification is discussed.