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The differentiation of metaphloem sieve element (MSEs) in the developing caryopsis of wheat (Triticum aestivum L.) was a programmed cell semi-death process. We studied the changes of microtubules and polysaccharide contents during MSEs development. Some significant features are presented in MSEs, such as cell wall non-uniform thickening, chromatin condensation and so on. During the period of MSEs differentiation, numerous microtubules are distributed in the vicinity of the cell wall, but finally they vanished in mature MSEs. Large glycoconjugates in the cell wall and small glycoconjugates in the Golgi apparatus were observed in the developing MSEs. Programmed cell death (PCD) ceased in the mature MSEs after 6 d after flowering and higher aggregation of glycoconjugates appeared in the cytoplasm. All of these processes were in tight contact with the cell wall non-uniform thickening during PCD.

The effects of waterlogging on amyloplasts and programmed cell death (PCD) in endosperm cells in Chinese wheat (Triticum aestivum L.; cv: Hua mai 8) are here discussed. Four water treatments were established from anthesis to maturity: they were 3 days of waterlogging treatment (DWT), 7 DWT, 12 DWT, and moderate water supply (the control). Lugol staining and scanning electron microscopy showed decreases in the number of amyloplasts and partially filled circular cavities under the waterlogging treatments. These resulted in serious deformities in the endosperm cells. Evans blue staining analysis and terminal deoxynucleotidyl transferase-mediated fluorescein deoxyuridine triphosphate nick-end labeling assays indicated that the PCD progression of endosperm cells occurred earlier under waterlogging treatments than in the control, so did the internucleosomal DNA fragmentation, which accompanies PCD in endosperm cells. Electron transmission microscopy analysis showed similar results. Under waterlogging treatments, the following PCD characteristics appeared earlier and were more pronounced than in normal endosperm cells: chromatin condensation, degradation of the nuclear envelope, swelling, and degradation of the mitochondrial cristae. Our study concluded that under waterlogging conditions, the number of amyloplasts tended to decrease and PCD was likely to appear ahead of time.

Features of programmed cell death (PCD) and dynamic changes of starch accumulation in developing pericarp cells of wheat (Triticum aestivum L.) were observed and analyzed by periodic acid-Schiff/toluidine blue O double staining, fluorescence staining, terminal deoxynucleotidyl transferase-mediated fluorescein deoxyuridine triphosphate nick-end labeling (TUNEL) and transmission electron microscopy. The results showed that cellular organelles were orderly disintegrated. TUNEL-positive nuclei were detected at 0 day after flowering (DAF), whereas nuclei showed significant features of degradation at 2 DAF, such as chromatin condensation, nuclei condensation, and nuclei deformation. Then, heterochromatin gradually disappeared and the cellular nucleus was completely degraded. The mitochondria degradation and vacuolation also were detected at 15 DAF. These results indicated that the development of pericarp cells was a typical process of PCD. However, the PCD in pericarp cells had their own characteristics: PCD started early and lasted for a considerable time. In the delayed process of PCD, starch granules were synthesized, deposited, and degraded temporarily in amyloplasts or chloroplasts. The delay of PCD in pericarp cells may be due to sufficient photosynthetic assimilates and energy supply. Besides, normal mitochondria were required for pericarp cells to survive. Pericarp cells contained only compound starch granules. Starch was massively synthesized from 0 to 11 DAF, but it was rapidly degraded after 11 DAF. Therefore, apart from protection, pericarp cells played essential roles in starch synthesis, storage, and degradation, as well as nutrient transportation.