XVI International Botanical Congess

Arginine is the major nitrogen source for the germinating soybean seed. To be utilized it is degraded via arginase, a mitochondrial enzyme.We assayed L-arginine uptake by purified mitochondria from soybean cotyledons. The uptake was complete in about 10 min. The label taken up was released by detergent. Cosedimentation of arginine and a mitochondrial marker enzyme activity confirmed mitochondrial arginine uptake. The rate of arginine uptake was not saturable with respect to arginine concentration at least up to 20 mM arginine, the highest concentration employed. Basic amino acids were the best inhibitors of arginine uptake. We are now examining the metabolic fate of intramitochondrial arginine. Rapid entry of arginine into seedling mitochondria is consistent with our reported increase in arginine expression and urea accumulation during soybean germination.