A method for isolating a high yield of Arabidopsis chloroplasts capable of efficient import of precursor proteins.

Chloroplasts were isolated from Arabidopsis plants grown under different conditions, and using different protocols, to determine a method that would yield chloroplasts capable of binding and importing precursor proteins. Chloroplasts isolated from protoplasts and purified on a Percoll gradient were highly import-competent, with little non-specific binding of the precursor, and a high yield of intact chloroplasts (0.1 mg chlorophyll/g FW). Chloroplasts from plants grown on agar plates had a much higher rate of import than those from plants grown on soil. Protein import remained high at all of the ages tested for chloroplasts from plate-grown plants, whereas it declined during the development of soil-grown plants. Arabidopsis chloroplasts imported a range of precursor proteins and had nucleotide requirements for binding and import similar to those reported for pea chloroplasts.