Oxidative and phosphorylative activity of mitochondria from pea cotyledons during maturation of the seed

The respiration rate and the activity of some mitochondrial enzymes from pea cotyledons have been followed during the final phases of seed development, when the relative water content of the cotyledons dropped from 65 to 13%. Succinate, malate and α-ketoglutarate oxidase activity, and succinate and malate dehydrogenase activity per cotyledon increased when the relative water content dropped from 65 to about 55%. A further drop of the relative water content was accompanied by a strong decrease of the activity of the succinate and malate oxidase system, but only a slight decrease of succinate and malate dehydrogenase activity. Mitochondrial fractions from air-dry, mature cotyledons showed a low activity of the succinate and malate oxidase system but their dehydrogenase activity was relatively high. The phosphorylation efficiency and respiratory control gradually decreased during maturation. These results indicate that during maturation of the pea seed certain mitochondrial enzymes partly lose their activity.