The structure of cortical cytoplasm in cold-treated tobacco cells:the role of the cytoskeleton and the endomembrane system.

Abstract

The eukaryotic cytoskeleton is a highly dynamic and complex structure supporting many basic metabolic processes. Generally, the organisation of cytoskeleton carries the spatial information important for various cellular compartments and moreover secures the mobility of protein-transporting membrane vesicles. One of the important features of cytoskeleton polymers is their high sensitivity to low (non-freezing) temperatures leading to reversible depolymerisation into subunits. However, cold sensitivity of cytoskeletal polymers differs in various plants and plant tissues depending on many interfering factors (Baluska et al., 1993; Egierszdorff and Kacperska, 2001; Kerr and Carter, 1990). In addition to that, spatial interconnection of cytoskeleton with endomembrane system plays an important role (for review see Lichtscheidl and Baluska, 2000). Coldinduced depolymerisation of both microtubules (MTs) and actin filaments (AFs) provided us with a tool to investigate the role of the cytoskeleton in the spatial organisation of the plant cell cytoplasm. The tobacco BY-2 suspension culture (Nagata et al., 1992) has been used as a model, physiologically homogenous plant cell line. We have focused on the cortical cytoplasm of BY-2 tobacco cells, where structural changes can be easily observed by conventional light and fluorescence microscopy (reviewed in Kumagai and Hasezawa, 2001). Together with this, the organisation of the endoplasmic reticulum (ER) was studied in vivo using BY-2 cells expressing a GFP-fusion protein targeted to the lumen of the ER. Protein analysis of cytoskeleton proteins was carried out to understand some cold-induced cytoskeletal changes on the protein level.