Biochemical Properties of Mitochondrial Membrane from Dry Pea Seeds and Changes in the Properties during Imbibition

An attempt to isolate intact mitochondria from dry pea seeds (Pisum sativum var. Alaska) ended in failure. Cytochrome oxidase in crude mitochondrial fraction from dry seeds was separated into three fractions by sucrose density gradient centrifugation. Two of the fractions contained malate dehydrogenase, whereas the other did not. Equilibrium centrifugation of mitochondrial membrane on sucrose gradients revealed that the membrane from the fraction without malate dehydrogenase was lighter than that from the others. Differences were observed in relative content of phospholipid to protein and in polypeptide composition analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis among the membranes from three fractions and imbibed cotyledons. Membrane from the fraction without malate dehydrogenase was rich in phospholipid and lacking in polypeptides with relatively high molecular weights as compared with that from others. During imbibition, the fraction without malate dehydrogenase and one of the other two disappeared rapidly after a lag phase lasting for at least 1 hour. Concomitantly, active and stable mitochondria increased in the cotyledons. The results were interpreted to indicate that there were at least three types of mitochondria in dry seeds, the membranes of which differed in their biochemical properties, and that the mitochondria became active and stable through assembly of protein into the membranes during imbibition.