Stromules: Mobile Protrusions and Interconnections Between Plastids

Abstract

Stroma‐filled tubules, recently named stromules, extend from the surface of plastids in most cell types and plant species examined. Stromules are highly dynamic structures, continuously and rapidly changing shape. They have been shown to interconnect plastids and permit the exchange of green fluorescent protein (GFP) between plastids. Stromules are enclosed by the inner and outer plastid envelope membranes and are 0.4 ‐ 0.8 μm in diameter and up to 65 μm long. Movement of stromules is dependent on the actin cytoskeleton and the ATPase activity of myosin. Stromules are more abundant in cells containing a relatively small plastid volume and provide a means of enormously increasing the plastid surface area. Many important questions on the structure, function and mobility of stromules remain unanswered.

New insights on stromules: Stroma filled tubules extended by independent plastids

“…The highly commendable studies performed earlier [1][2][3][4][5][6][7][8][9][10][11][12] had firmly established the presence of stromules as plastidic extensions. The recent findings reaffirm the uniqueness of plastids and strongly suggest that stromules do not act as conduits for inter-plastid communication but as important extensions that increase plastid interactions with the rest of the cytoplasm (Fig.…”

“…15 Further many plant biologists have probably not critically assessed the experimental design reported in original publications [3][4][5][6][7][8] and appear to think of stromules as tubular interconnections between plastids. 9,16 The recognition of stromules as sporadically extended stroma filled tubules from all kinds of plastids constitutes one of the major insights that resulted from the direct application of green fluorescent protein aided imaging of living plant cells. Observations of dynamic green fluorescent stromules strongly suggested that plastids frequently interact with each other while photo-bleaching of interconnected plastids indicated that proteins can move within the stroma filled tubules.…”

“…4,7,8 Since their re-discovery numerous conditions leading to stromule induction have been reported in original publications and discussed in several reviews. [5][6][7][8][9][10][11][12][13][14] The authoritative review by Hanson and Sattarzadeh 12 specifically appraised the status of stromules and provided a balanced discussion on the different possible roles that stromules might play within the cell. Most importantly this review clearly states that "most plastids are not connected at any one time, although over the course of a day, it is possible that many plastids within a cell establish transient contacts through stromules".…”

Chloroplasts in Living Cells and the String-of-Grana Concept of Chloroplast Structure Revisited

“…Chloroplasts in a living mesophyll cell of spinach observed by phase microscopy. G -granum; J -chloroplast jacket; M -mitochondrion; S -starch grain (from Spencer and Wildman 1962). 2001; Gray et al 2001). In contrast to the stroma phase of the chloroplast, the thylakoid system with its associated grana does not undergo rapid changes in shape.…”

Morphological and Ultrastructural Changes of Organelles in Leaf Mesophyll Cells of the Arctic and Antarctic Plants of Poaceae Family Under Cold Influence

“…It is believed that cytoskeletal elements could participate in the formation and stabilization of protrusions (Gray et al, 2001). The endoplasmic reticulum probably aids chloroplast protrusions in the process of transporting metabolites and signal molecules (Schattat et al, 2011).…”