Vacuoles occupy 80–90% of a mature plant cell and mainly contribute to all types of cell expansion. Zeocin, an inducer of DNA double-strand breaks, causes cell expansion with endoreduplication. The vacuolar structure after zeocin treatment was examined in tobacco (Nicotiana tabacum) cultured cells expressing GFP fused to a vacuole membrane protein. We found that the genotoxic stress induced the cell expansion with subdivision of the vacuolar lumen by cytoplasmic strands. When a femtosecond laser was used to cut off the cytoplasmic strand, mitochondrial transport along the strand stopped. This suggested that in the elongated cells under the genotoxic stress, the transport of subcellular materials was activated for DNA repair within the damaged cell nucleus by the construction of a network of cytoplasmic strands in the vacuolar lumen.
