Successive changes in the ultrastructure ofOryza sativa L. cells during growth and aging

The ultrastructure ofOryza sativa L. cells in suspension was determined as cells developed, matured and senesced at 3, 10, and 17 days, respectively, after transfer to fresh medium. Although cultures of 3-day-old cells contained some senescent cells, the symptoms of cell aging were very conspicuous at 10 days and were most pronounced at 17 days. The amount of cytoplasm decreased as the number of lytic areas, myelin figures and vesicle bodies increased. Other noticeable subcellular changes observed were ultrastructural modifications of mitochondria, proplastids, amyloplasts, and nuclei. Such changes were associated with a general deterioration of the lipoprotein complex of the cell during its growth. A fibrous structure without an external membrane was observed and its reported for the first time for cells grown in suspension culture.