Plastid and Stromule Morphogenesis in Tomato

By using green fluorescent protein targeted to the plastid organelle in tomato (Lycopersicon esculentum Mill.), the morphology of plastids and their associated stromules in epidermal cells and trichomes from stems and petioles and in the chromoplasts of pericarp cells in the tomato fruit has been revealed. A novel characteristic of tomato stromules is the presence of extensive bead-like structures along the stromules that are often observed as free vesicles, distinct from and apparently unconnected to the plastid body. Interconnections between the red pigmented chromoplast bodies are common in fruit pericarp cells suggesting that chromoplasts could form a complex network in this cell type. The potential implications for carotenoid biosynthesis in tomato fruit and for vesicles originating from beaded stromules as a secretory mechanism for plastids in glandular trichomes of tomato is discussed.