Studies On The Degeneration Of Nucleus And Cytoplasm Development Of Starchy Endosperm During PCD In Triticeae Crops

Programmed Cell Death (PCD) of starch endosperm and the development of starch granules and protein body in the wheat and barley endosperm during development were studied in this thesis. Some properties of starch granules were also investigated. The main results were as follows.1, Studies on the PCD of starch endosperm. Conventional ultrastructural observation showed that at the middle and late stage of endosperm development, several distinct morphological features of PCD had been found on the nucleus of starch endosperm, e.g. nucleus deformation, chromatin condensation, nuclear envelope disruption, and nuclear matrix leakage. The DAPI staining also showed that the nucleus turned from uniform morphology to unshaped form, and finally degraded into nuclear residues which spread in the clearance starch granules. Along with the development of endosperm, TUNEL experiments demonstrated nucleus DNA fragmentation and the nuclear showed DNA laddering when analyzed by agarose gel electrophoresis. Evan's blue staining indicated that the initiation and spread of starchy endosperm cell death occurred stochastically. The above results proved that the cell death of starch endosperm in wheat and barley was a PCD process. Starch granules and storage proteins were continually synthesized and accumulated in the starch endosperm cells despite the nucleus degradation. The denucleated cell which had abundant of cell organelles in cytoplast still remained normal metabolic activity. The activities of SOD (Superoxide dismutase), POD (Peroxidase) and CAT (Catalase) maintained a certain level and the grain weight also increase during later-developing stage. The above results indicated that after the nucleus disintergration , starch endosperm cell did not die at once. The PCD of starch endosperm in wheat and barley differed from the PCD in most plants where the nucleus was the last organelle to disappear, so the PCD of starch endosperm in the two plants was a kind of spacial phenomenon.2. Studies on the development and properties of endosperm starch granules. The observation of SEM and TEM all showed that large starch granules formed and developed at the young stage of wheat and barley endosperm development. Amyloplast coming from proplastid with large starch granules could produce new amyloplast by the way of constricting and budding off. One amyloplast had only one large starch granule indicating large starch granules were single starch granule. Small starch granules could form and develop at the middle and late stage of endosperm development. Many amyloplasts which would produce small starch granules came from the envelope protrusion of amyloplast with large starch granules. Amyloplasts with small starch granules could also form new amyloplasts to produce small starch granules by the way of constricting and protruding of their envelopes. Many small starch granules could form and develop in one amyloplast. Small starch granules were compound starch granules. The amyloplast envelope began to degrade and released starch granules into cell matrix when amyloplast was full of starch granules. During the development of endosperm, there was no detectable difference in the morphology between large granules and small granules. However differences existed among varieties of size, amylose content, thermal properties and crystalline properties between large granules and small granules.3. Development of Protein Body (PB). Observation of TEM showed that developing endosperm accumulated storage proteins in the protein storage vacuole (PSV). Concrete ways how storage proteins were exported from endoplasmic reticulum(ER) to the PSV were different in the wheat and barley endosperm. Golgi apparatus were involved in the transportation of storage proteins in wheat endosperm, while storage proteins in barley endosperm were stored in the ER and exported to the PSV at last.