PURIFICATION OF CHLOROPLASTS FROM FRUITS OF GREEN-PEPPER (CAPSICUM-ANNUUM L) AND CHARACTERIZATION OF STARCH SYNTHESIS - EVIDENCE FOR A FUNCTIONAL CHLOROPLASTIC HEXOSE-PHOSPHATE TRANSLOCATOR

We have developed a method for the purification of chloroplasts from g reen-pepper fruits. These chloroplasts are characterized by a high deg ree of intactness and low contamination with other cellular components . The purified chloroplasts perform CO2 fixation and posses a fructose -1,6-bisphosphate phosphatase, necessary for the conversion of CO2 to starch. Besides carbon dioxide, these chloroplasts take up external ca rbon skeletons as precursors for starch synthesis. From various potent ial precursors tested, glucose-ti-phosphate (Glc6P) is used with the h ighest efficiency for starch synthesis. The Glc6P-dependent starch syn thesis is strongly enhanced in the presence of light, ATP, and phospho glyceric acid. Adenosine 5'-monophosphate acts as an inhibitor of ATP- stimulated Glc6P-dependent starch synthesis. The ability to use Glc6P as a precursor for starch synthesis indicates the presence of a functi onal hexose-phosphate translocator in isolated chloroplasts from green -pepper fruits. The results are discussed with respect to the physiolo gical function of chloroplasts in fruit tissues. We predict that chlor oplasts from green-pepper fruits possess a chloroplastic hexose-phosph ate translocator which enables these plastids to maintain starch synth esis from cytosolic precursors during both day and night.