Induction and regulation of chloroplast replication in mature tobacco leaf tissue.

Chloroplast replication was induced in mature tobacco leaf tissue (Nicotiana tabacum L.) by culturing leaf discs on a sterile medium composed of salts and sucrose. Chloroplast replicaton is greatly enhanced by the addition of kinetin to this medium. Kinetin also enhances cell enlargement, but cell division does not occur. Chloroplast replication is nonsynchronous and proceeds most rapidly when the cell enlargement rate decreases. Chloroplast replication is light-dependent, but cell enlargement occurs in both light and dark. Chloroplast replication resumes when discs cultured in the dark are returned to the light. It appears that chloroplast replication is related to cell expansion. The possibility of inducing synchronous replication of chloroplasts in tobacco cells is discussed.