Abstract:The development of mitochondria in the course, of imbibition ofmung bean cotyledons was studied. Mitochondria were prepared by differential centrifugation, and purified by discontinuous sucrose, density gradient centrifugation. Theelectron micrographs revealed that the mitochondria isolated from dry seeds cotyledonslook like small vesicles, when cotyledons were imbibed for two hours, the mitochondrial cristae were not observed, but after four hours, a few cristae appeared on the innermembrane. Till 12 hours, the inner membrane systems wore well-developed. Al this time.all the space in mitochondria are filled with cristae. With the structural integrity of the mitochondria, the functions of oxidation and phosphorylation were graduallyshown, For instance, ADP/O ratio and RCR were not able to be measured in the imbibition of 2 and 4 hours, but at 6th hours, ADP/O Was increased by 0.6, RCR nearly 2.0, After 24 hours imbibition, ADP/O and RCR were increased to 1.5 and 3.5 respectively. The activity of cytochrome oxidase reached the highest after imbibition for 3 hours (2.54 OD/mg protein/min). If cotyledons were imbibed continuously, the activityof this enzyme in mitochondria remained constant. The activity of ATPase located onthe inside of the mitochondrial inner membrane was gradually enhanced from the beginnning of imbibition. These results suggest that the assembly of cytochrome oxidaseand ATPase on mitochondrial membrane may not be synchronous.