Femtosecond laser perforation of plant cells for evaluation of cell stiffness

Stiffness of plant cells is affected not only by the cell wall elasticity but also by intracellular turgor pressure. Atomic force microscopy (AFM) has been used for evaluating cell stiffness; however, it is difficult to evaluate these contributions based only on AFM measurements. Therefore, we considered applying laser perforation to the individual control of the turgor pressure of the cell for the AFM measurements. When an intense femtosecond laser was irradiated onto the cell surface, an ablation hole with a few micrometer diameter was formed on the cell wall. The ablation hole connected the intracellular and the extracellular fluid, releasing intracellular pressure due to the turgor pressure of vacuous. The cell stiffness before and after the laser perforation was investigated by an AFM indentation test and estimated using Hertz contact theory as a measure of Young's modulus. Young's modulus was drastically decreased by the laser perforation. This result clearly suggested that Young's modulus is not only due to elasticity of the cell wall but also due to the turgor pressure. We concluded that the laser perforation is a promising way to reveal cell wall stiffness with force interaction between the cell wall elasticity and the intracellular turgor pressure.