Morphological changes in the cytoskeleton, nuclei, and vacuoles during cell death of short-lived ray tracheids in the conifer Pinus densiflora

摘要

Morphological changes in the cytoskeleton, nuclei, and vacuoles were monitored during the cell death of short-lived ray tracheids in the conifer Pinus densiflora. After formation of the dentate thickenings that occurred at the final stage of formation of cell walls, organelles started to disappear in differentiating ray tracheids. First, the microtubules and vacuoles disappeared. Then actin filaments disappeared in the differentiating ray tracheids adjacent to ray tracheids that lacked nuclei, and, finally, the nuclei disappeared. These features indicate that cell death in ray tracheids might differ from the programmed cell death of tracheary elements that has been studied in vitro in the Zinnia culture system.