Plant Cell Motility and Laser Microsurgery of Cytoplasmic Strands

     Author: Franz Hoffmann

Plant cells are shaped by rigid cell walls. Osmotic forces press the plasma membrane tightly against these walls. The walls can be removed with enzymes. The remaining structures, the protoplasts, are now bordered by the plasma membrane. Since the shaping force of the wall is missing, isolated plant protoplasts are usually perfectly spherical in shape as a result of non-directional osmotic forces. However, not all isolated plant protoplasts are spherical. Through cytoplasmic streaming, cytoplasmic strands continuously change their length, branching and attachment, and as a result the shape of the protoplast may change. A laser microsurgery experiment provides proof that the inner tension built by the cytoplasmic network is moving the cell. A laser beam focused at a cytoplasmic strand will cut the strand and cause the network to collapse without destroying the integrity of the cell. As a result osmotic forces can take over and round the protoplast. Moving around is not an option for most cells of higher plants, and cytoplasmic streaming serves normally the intracellular transport - but they have not totally lost the basic skills that would enable them to move.