The effect of laser microsurgery on cytoplasmic strands and cytoplasmic streaming in isolated plant protoplasts.

Cytoplasmic strands of actively streaming isolated callus derived protoplasts of higher plants were subjected to laser microsurgery. Typically, the irradiated strand retracted and cytoplasmic streaming stopped in the entire cell. At the same time, all cytoplasmic strands disintegrated, and formerly not totally spherically shaped protoplasts became spherical. This result indicates tension as a stability factor of cell shape and the cytoplasmic make-up and demonstrates that the nonspherical shape of these protoplasts is not due to cell wall residues. Cytoplasmic streaming as well as the strands were quickly reestablished and often the irregular shape of the protoplast appeared again. Treatment of unirradiated cells with cytochalasin B showed similar effects. The results are discussed with respect to the involvement of cytoskeletal elements in cytoplasmic streaming and organization.