DNA biosynthesis in chloroplasts and its regulation: Studies on isolated chloroplasts and chloroplast extracts
During leaf development, chloroplasts are formed by the binary fission of pre-existing plastids (1); thus, replication of chloroplast DNA (ctDNA) must occur to maintain an adequate amount in each organelle. The levels of ctDNA in plastids vary during plant development (2); the fraction of chloroplast DNA increases during early shoot development then stabilizes thereafter. The number of genome copies per plastid also increases early, however, they reach a maximum then decline as tissues mature. Such variation in the levels of ctDNA suggests that the capacity of chloroplasts to replicate their DNA changes during development. Here, we describe the use of both isolated intact pea chloroplasts and plastid extracts to study developmental changes in ctDNA biosynthesis.