Minisymposium 23: Cytoskeleton

Abs # 37001: Microtubules and microfilaments control the movement and morphology of non-green plastids and stromules

Presenter:	Kwok, Ernie Y., eyk5@cornell.edu
Authors	Kwok, Ernie Y. (A)   Hanson, Maureen R. (A)
Affiliations:	(A): Department of Molecular Biology and Genetics, Cornell University

Stromules are dynamic extensions of the plastid envelope membrane that allow protein trafficking between plastids. While stromules (stroma-filled tubules) have been observed previously, their study was limited by technical difficulty in observing them by conventional light and electron microscopy. However, recent use of plastid-targeted GFP has allowed us to observe stromules in chloroplasts as well as non-green plastids throughout the living plant. Inspection of plastids in tobacco and other higher plants has shown that stromules are most frequently found in non-green tissues such as flower-petals, cultured cells, and roots. Stromules often join adjacent plastids within a cell. Photobleaching studies have confirmed that GFP can traffic from plastid to plastid via these interconnecting stromules. Stromules are also highly dynamic structures, rapidly extending from and contracting back to plastid bodies. As yet, no definite role for stromules in plant cells has been established. Do they facilitate the movement of proteins or other molecules between plastids? Do they promote exchange of molecules between plastids and other cellular organelles? Are they involved in movement of plastids within the cell? We are approaching these questions by studying the mechanisms that control the structure and movement of stromules. In higher plants, actin microfilaments are believed to promote chloroplast movement in response to light. Indeed, most organelles appear to move within plant cells via actin. We have used inhibitors of the actin and tubulin cytoskeletons to determine which systems control the structure and movement of non-green plastids and their associated stromules. Our results indicate that both microfilaments and microtubules control the length of plastids and their mechanisms of action are independent. Microfilaments promote the majority of plastid and stromule movement while microtubules appear to inhibit their movement. Interestingly, we have found that actin’s structural and motile influence on stromules are independent: stromules are not a precondition for plastid movement and stromules do not require plastid movement in order to form. Finally, we have observed that trafficking of GFP through stromules is not severely affected by inhibitors of either actin or tubulin. (Research funded by DOE Energy Biosciences)