Programmed cell death is known to be an essential process for tracheary elements and sieve elements. Tracheary elements undergo PCD, which forms a tubular channel for transporting water, while sieve elements go through programmed cell semideath process to transport organic nutrients.Biological electron microscopy and ultracytochemical technology was used to further clarify the ultrastructural changes and ACPase dynamic distribution of sieve elements and tracheary elements in wheat (Triticumaestivum L.) caryopsis development. The dynamic changes and the distribution of active products of ACPase were studied. Results showed that the sieve elements were distributed as semi-circular at the outside of tracheary elements.The degradation of the nucleus in sieve element was later than that in tracheary elements. The organelles were wrapped by the autophagosome for degradation in the process of developing sieve elements.The mature sieve element retains some organelle fragment and is alive.When the tonoplast in tracheary elements was ruptured, the cytoplasm were degraded by the vesicles in the cell and the cytoplasm was completely degraded. Fully degraded tracheary elements were obviously dead.After the tonoplast was ruptured, ACPase as a key enzyme of vacuole in organelles including mitochondria of tracheary elements was most notable. In the development of sieve element, ACPase activity was detected in the mitochondria and the plasmodesmata of the mature sieve cells. It is indicated that ACPase may be involved in the transportion of materials between cells.