The Effect of Cytochalasins C and D on the Rate of Cytoplasmic Streaming

The effect of cytochalasins C and D on the rate of cytoplasmic streaming

Introduction:

Cytoplasmic streaming, also termed cyclosis, is the circulation of cytoplasm within cells (Campbell et al., 2009). It was first discovered by Corti in 1774 and has been observed in many eukaryotic cells, especially in plant species, ranging from algae to higher plants and fungi (Shimmen et al., 1994). Cytoplasmic streaming facilitates the distribution of molecules and vesicles within large cells. It also enables the mobility of organelles such as endoplasmic reticulum, golgi apparatus, peroxisomes and mitochondria (Verchot-Lubicz et al., 2010). Cessation of cytoplasmic streaming is generally assumed to indicate cell death (Bishop et al., 1949).

Cytoplasmic streaming is a typical example of actin-based motility process (Kinkema et al., 1994). Actin is a globular protein that makes up twisted double chains of microfilaments (or actin filaments), one of the three components of cytoskeleton. Microfilaments are dynamic, which means that they can undergo polymerisation or depolymerisation by adding or removing actin proteins. In plant cells, actin filaments are organised into two main arrays. The filaments forming a three-dimensional network in the ectoplasm (or the cortex) give it a gel-like consistency. In contrast, the filaments displaying a parallel arrangement in the endoplasm give it a sol-like fluid state (Campbell et al., 2009). In 1956, the motive force for cytoplasmic streaming was suggested to be localised at the interface between the nonmoving ectoplasm and the streaming ectoplasm (Kamiya et al., 1956) and involvement of actin-myosin interaction was later identified (Shimmen et al., 1994).

Myosin is a family of motor proteins, which form dimers with two amino-terminal heads and a tail. The head regions of myosin proteins have ATPase and motor activity which enables them to ‘walk’ along the actin filaments using the hydrolysis energy of ATP, and the tail region is involved in binding to organelles (Reichelt et al. 2000). The key force-generating step