Biogenesis of Mitochondria in Imbibed Peanut Cotyledons : II. DEVELOPMENT OF LIGHT AND HEAVY MITOCHONDRIA.

THERE ARE TWO TYPES OF MITOCHONDRIA PRESENT IN IMBIBED PEANUT COTYLEDONS: a light type (density 1.182 grams per cubic centimeter) and a heavy type (density 1.205 grams per cubic centimeter). The membrane fractions from these two types can be distinguished using sucrose density gradient analysis, and differences in membrane density between the light and heavy types are reflected in differences in their protein N and phospholipid P composition. With increasing time after imbibition, there is a substantial increase in the amount and activity of the light type of mitochondria due to their de novo synthesis. The membrane density of the light mitochondrial fraction declines over 5 days after the start of imbibition as the phospholipid P to protein N ratio increases. The heavy mitochondrial fraction declines during the first 3 days after the start of imbibition, and then it remains at a low, but constant, level thereafter. Even during the decline, however, there is synthesis of proteins comparable to that into light mitochondria. The mitochondrial biogenesis that has been observed in peanut cotyledons is of the light type, the function and physiological importance of the minor heavy type is not known.