Abstract
Mature plant cells contain large central vacuoles that occupy up to 95% of the total cell volume. It is still unclear how these vacuoles are generated. To investigate this process, we examined Arabidopsis and Tobacco root tip tissues that contain vacuoles of various sizes during different stages of cell development. To observe the dynamic membrane structure, we used the high-pressure freezing/freeze-substitution method (HPF/FS). The anti-vacuolar H+-pyrophosphatase (V-PPase) antibody was used for immunogold labeling of Arabidopsis and Tobacco root tip cells, and positive signals in the vacuolar membrane and a novel ring-like structure were detected. This ring-like structure was a flat and/or double-membrane structure that surrounded a cytoplasmic component. Further, we observed some ring-like structures fused with one another or fused with the central vacuoles. These ring-like structures were expected to develop into vacuoles. In addition, we found that the complex structures that fused with several ring-like structures were mainly present in the stele and not in meristematic cells. These ring-like structures containing V-PPase may play an important role in vacuole formation.
