Characterization of stromules visualized in transplastomic plants expressing green fluorescent protein (GFP)

摘要

The surface of plastids is bounded by an envelope consisting of two membranes. Most macromolecules, such as proteins and nucleic acids are not able to penetrate the inner membrane of t he envelope. Thus, chloroplasts in general have been consideredas discrete organelles. Green fluorescent protein (GFP) is a powerful tool to visualize the subcellular structures of organelles in living cells. Recently Koller et al. (1997) visualized the tubular projections emanating from chloroplasts in nuclear transgenic plants targeting GFP into chloroplasts. Sometimes tubules connect the chloroplasts with each other and GFP molecules are exchanged rapidly betweent heconnected chloroplasts through the tubules. Stroma-containing protuberances were visualized by the electron microscopy in rice leaves preserved by high-pressure freezing (Bourett et al., 1999). Since the chloroplast tubules contain the extended stroma, they are named as 'stromules' The stromules are rare in leaf mesophyll cells containing chloroplasts, but they are abundant in chlorophyll-free cells, such as root, petal and tissue culture, indicating that stromules are developmentally regulated.