Cell optical displacement assay (CODA) - Measurements of cytoskeletal tension in living plant cells with a laser optical trap

This chapter focuses on the technique of optical trapping and demonstrates its unique and powerful role as a quantitative tool for measuring the elasticity of individual actin cables in living plant cells. The trapping beam is positioned at a point on the filament between the nucleus and the membrane/wall for each attempt in the cell optical displacement assay (CODA). To ensure that the trapping intensity does not damage the fibers, each displacement at a particular power setting is performed five times and, in all instances, the fiber is required to rebound to the original position following termination of the trap. All trapping experiments can be recorded on videotape and individual pictures can be prepared frame-by-frame from the tapes. Although the technique is described for plant cells grown in suspension culture, this technique can also be extended to whole plant measurements in root cells and root hairs. This capability facilitates the use of this technology for measurements in plants that have been subjected to a variety of genetic manipulations and environmental conditions. It can also be exploited to measure changes in the cytoskeleton during infection thread formation that occurs following the attachment of Bradyrhizobium japonicum to soybean root hairs. © 1995 Academic Press Inc.