| Three maize cultivars(Z,N,T),were used in the present study .The effects of 6-BA on the development of maize endosperm after pollination were investigated by the physiological and biochemical method with the characteristic of hormone, the number of endosperm, the kernel nutriment content. The characteristic of different maize of endosperm programmed cell death and the effects of 6-BA on the endosperm programmed cell death with the optical microscope, transmission electro microscope, molecular biology, respectively. The main results were follows:1 The effects of exogenous 6-BA on the number of endosperm cellThe endosperm cell numbers were determined. The numbers of different maize endosperm were increased by the different 6-BA concentration. But the effects degree of 6-BA were different on three maize cultivars. Compared to the contrast, the endosperm cell numbers of Z and T. were prominently increased but N. It was probably one of the important causes to improve grain yield by spraying this regulator.2 The effects of exogenous 6-BA on endogenous hormones contentsEndogenous hormones contents in endosperm were measured for each treatment. The results indicated that 6-BA had different effects on endogenous hormones at different grain filling stages. Compared to the control , discrepancy between the treatments of Z and T were prominent but N, the content of Z+ZR, GA were increased by the increased concentration; the iPA content in the early grain filling stage of three maize cultivars was prominently enhanced; notably restrained the accumulation of ABA; the IAA content was notably increased in the early and late stage grain filling of Z, in the late grain filling stage of N, in the early grain filling stage and decreased in the late grain filling stage of T. Under this experiment the changes of endogenous hormones were probably one of the important causes led to variations of yield and quality. 3 The effects of exogenous 6-BA on the content of nutritious substanceThe content of nutritious substance were significantly increased in different grain filling stage, including the content of sucrose in the early and middle grain filling stage, the content of protein in the entire grain filling stage, the content of amylopection, total starch of a grain in the late filling stage.4 The characteristic of maize endosperm PCDConventional ultrastructural observation showed that the starchy endosperm cells of maize underwent nucleus deformation, nucleus disintegration, nucleus residue formation and chromatin condensation. In the process of nucleus disintegration, mitochondrion also showed a series of structural changes, such as the cristae of mitochondrion disappeared, resulting in central hollowed mitochondrion. The above results proved that the cell death of starchy endosperm in maize was a PCD process. Evans Blue staining proved that death of endosperm cell started the top of endosperm and expanded toward adown and forth of endosperm. The results of ultrastructual observation and Evans Blue staining proved that 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 endosperm cells in maize.5 The effects of exogenous 6-BA on the PCD of EndospermTreatment with 6-BA reduced the extent of DNA fragmentation in developing starchy endosperm cells and the reduced degree increased with the concentration of 6-BA. Evans Blue staining proved that the blue area lessen compared to control. The results of ultrastructual observation proved the degree of nucleus disintegration lessen compared to control. It proved that the 6-BA may lessen the endosperm cell PCD, probably one of the important causes leading to variations of yield and quality. |
