ENERGY REQUIREMENT FOR THE IMPORT OF PROTEIN INTO PLASTIDS FROM DEVELOPING ENDOSPERM OF RICINUS-COMMUNIS L

Leucoplasts isolated from developing endosperm of Ricinus communis L. will import the precursor of the small subunit of ribulose bisphosphate carboxylase from pea shoots and process it to its mature molecular weight (SA Boyle, SM Hemmingsen, DT Dennis [1986] Plant Physio) 81: 817-822). This process requires energy in the form of ATP. GTP, CTP, and DTP are inactive. ADP will also satisfy the energy requirement, probably through the action of adenylate kinase in the envelope. Fatty acid biosynthesis which occurs within these leucoplasts also requires ATP for maximal activity. Phosphoeno/pyruvate will stimulate fatty acid biosynthesis approximately three times as effectively as ATP through the generation of ATP within the organelle by the action of the plastid pyruvate kinase. However, phosphoeno/pyruvate under similar conditions will not stimulate the uptake of the small subunit of ribulose bisphosphate carboxylase into leucoplasts. These results indicate that ATP is required outside the leucoplast for protein uptake and that internally generated ATP is not effective in this process.