Optical Trapping in Plant Cells - Plant Cell Morphogenesis: Methods and Protocols - page 249

Chapter 22

Optical Trapping in Plant Cells

Tijs Ketelaar , Norbert de Ruijter , and Stefan Niehren

Abstract

Optical tweezers allow noninvasive manipulation of subcellular compartments to study their physical inter-
actions and attachments. By measuring (delay of) displacements, (semi-)quantitative force measurements
within a living cell can be performed. In this chapter, we provide practical tips for setting up such experi-
ments paying special attention to the technical considerations for integrating optical tweezers into a confo-
cal microscope. Next, we describe some working protocols to trap intracellular structures in plant cells.

Key words Optical tweezers, Optical trap, Confocal microscope, Noninvasive manipulation, Plant
cell, Cytoskeleton, Endomembrane system

1 Introduction

Optical tweezers use gradient light forces for attracting (sub-)
micrometer-sized particles in a highly focused laser beam. Differences
in refractive indices cause a total force pointing towards the center of
the diffraction-limited spot. If the diffraction index of the particle is
higher than the index of the surrounding medium, the force is
attractive and creates an optical trap. Generally, infrared laser radia-
tion is used for optical trapping since the absorbance of light with
wavelengths in the infrared range is extremely low in most biological
materials. For more information about optical trapping, see ref. [ 1 ].
Optical trapping is often used in in vitro experiments in which
conditions can be controlled. Nevertheless, optical trapping of
subcellular compartments with a high refractive index is also pos-
sible in intact, live cells. In plant cells, these types of experiments
have greatly improved our understanding of physical aspects of
intracellular organization [ 2 , 3 ].
In in vitro studies, optical trapping is often combined with
wide-fi eld fl uorescence microscopy to obtain positional informa-
tion of fl uorescently tagged molecules or beads. Plant cells are
often large, embedded in tissues, and cell walls or other cell con-
stituents can give autofl uorescence. Thus, imaging of fl uorescence