Development of a method to measure mechanical properties of single elongated callose fibers in protoplast cultures of Larix leptolepis and Betula platyphylla

We developed a method to measure mechanical properties of single fibers of callose in liquid protoplast cultures of Larix leptolepis and Betula platyphylla, which were formed in media containing 50 mM of MgCl2 or 100 mM of CaCl2, respectively. Tensile test was performed using two micromanipulators loading micropipettes under an inverted microscope. Spring constant of the pipette used was first calibrated and calculated from using a microbalance. The callose fiber was wired between the two micropipettes. The Young’s modulus of single fibers for Larix and Betula was 7-9 kPa (1.4-1.9 x 104 N/m2) though the diameters of the fiber varied from 10 μm for Larix and 22-26 μm for Betula. No difference was found between experiments with and without medium containing high concentrations of salts. Tensile strength at break was 1.1-1.8 kPa (2.3-3.6 x 103 N/m2). The values are compared to other materials including cellulose containing plant cell wall, cell membranes, and amorphous callose. The value of the Young’s modulus observed was discussed.