Stromules (stroma-filled tubules) are highly dynamic structures extending from the surface of all plastid types, including proplastids, chloroplasts, etioplasts, leucoplasts, amyloplasts, and chromoplasts.
Protrusions from and interconnections between plastids were observed in 1888 (Gottlieb Haberlandt) and 1908 (Gustav Senn) and have been described sporadically in the literature since then.
[1][2][3][4] Stromules were recently rediscovered in 1997[5] and have since been reported to exist in a number of angiosperm species including Arabidopsis thaliana, wheat, rice and tomato, but their role is not yet fully understood.
[7] This dynamic random walk-like movement is probably caused by Myosin XI proteins as a recent work found.
Other functions of stromules, such as transfer of macromolecules between plastids and starch granule formation in cereal endosperm, may be restricted to particular tissues and cell types.