Chloroplast Division and DNA Synthesis in Light-grown Wheat Leaves

Light-grown 7-day-old wheat seedlings (Triticum aestivum, var. Maris Dove) showed an increase of 200% in plastids per cell between 1.7 and 4.5 centimeters from the leaf base. This increase was the result of divisions of young chloroplasts at various stages of development, and was well separated in distance, and therefore in time from the region of cell division in the basal meristem. [³H]Thymidine was incorporated into plastid DNA throughout the zone of plastid division, but not above it.