Stromules and the dynamic nature of plastid morphology

Investigation of plastids via green fluorescent protein (GFP) has led to the rediscovery of tubular extensions of the plastid membrane, termed stromules, for stroma-filled tubules. These unique structures are challenging our understanding of plastid structure and function. Stromules are highly dynamic, branching and elongating across the plant cell. Recent experiments indicate that cytoplasmic microtubules and microfilaments control the shape and motility of stromules. Whether stromule formation involves plastid-specific structural systems, such as the plastid division machinery, remains open to debate. Fluorescence photobleaching experiments have revealed that GFP can traffic between plastids joined by stromules. As a result, interest has grown in whether other macromolecules can also travel through these connections. Although the function of stromules is unknown, several aspects of their biology suggest they play a role in molecular exchange between plastids and other organelles.