| Programmed Cell Death (PCD) is a gene-regulated and initiative cell death. It covers all fields of plant development and has been an attractive issue in the research of plants. In this dissertation, rice (Oryza sativa L.) cultivar Shen Tai No.l and wheat (Triticum Aestivum L.) cultivar E En No. 1 were used, and the PCD processes of starchy endosperm in the two plants during development were studied. Because the filling and development of endosperm cells play a great role hi the yield and quality of cereal grains, in this thesis, the genesis and development of amyloplast in the starchy endosperm cells were studied, and the affections of exogenous hormones on the development of starchy endosperm cells were also reported. The main results of this paper were as follows.1. The PCD processes of starchy endosperm cells in rice and wheat1.1 Conventional ultrastructural observation showed that the starchy endosperm cells of rice and wheat underwent nucleus deformation. nucleus disintegration. nucleus residue formation and chromatin condensation. In the process of nucleus disintegration, mitochondrion and endoplasmic reticulum also showed a series of structural changes, such as the cristae of mitochondrion disappeared, resulting in central hollowed mitochondrion; endoplasmic reticulum formed phagosome, and then swallowed cell matrix and organelles. The above results proved that the cell death of starchy endosperm in rice and wheat was a PCD process.1.2 The results of ultrastructural observation^ Evans Blue staining and grain filling research proved that the PCD of starchy endosperm cells in rice and wheat during development was a kind of special phenomenon. It showed some special features:(1) The nucleus of starchy endosperm cell in rice and wheat was the first organelle to suffer from degeneration. Even after nucleus disintegration, the starchy endosperm cell still remained alive, and the reserves including starch and storage proteins were still synthesized and accumulated in the cell as normal. It was the date of cell death until the cell was filled with starch. At this time, it claimed the end of PCD procedures. Therefore, the PCD processes of starchy endosperm cells in rice and wheat consisted of two steps: nucleus disintegration and the non-nucleated development after nucleus disintegration.The PCD of starchy endosperm in rice and wheat differed from the PCD in most plants, because in most plant cells, nucleus was the last organelle to disappear and non-nucleated development didn't exist.(2) In the starchy endosperm cells of rice and wheat the chromatin condensed but didn't show typical marginalization.(3) The nucleus of starchy endosperm cell hi rice and wheat suffered from deformation severely, and it could be split into several nuclear residues by the cleavage of nuclear envelope; while in other plant cells this phenomenon could rarely be observed.(4) No formation of apoptotic bodies could be found in the starchy endosperm cells of rice and wheat. The dead starchy endosperm cells functioned as a specific reservoir that accumulated and stored starch and storage proteins.1.3 Evans Blue staining and DNA electrophoresis analysis proved that the PCD of starchy endosperm cells in rice differed from that in wheat at some aspects. The nuclear DNA of starchy endosperm cells in rice degenerated but couldn't show a ladder of DNA fragments, while the nuclear DNA of starchy endosperm cells in wheat showed typical DNA laddering when resolved on agarose gel. In addition, the initiation and progression of cell death in wheat starchy endosperm was stochastic, while the cell death of central starchy endosperm in rice was earlier than that of other regions, though the initiation of cell death in rice starchy endosperm was not highly orderly.2. The genesis and development of the amyloplast in rice starchy endosperm cellsAmyloplast produce new amyloplast by the action of its envelope. Minor starch grain can be contained hi the amyloplast. When the starch grain grows bigger, the amyloplast changes into...
|
PDF Full Text Request