| Cotton is an important economic crop and its fiber development influences cotton's production and quality greatly. Programmed cell death (PCD) of cotton fiber cells influence fiber's qualities, such as fiber length and intension. Therefore, research on cotton fiber's PCD can help us understand how to improve cotton fiber's properties and production of cotton. In this dissertation, cotton (Gossypium hirsutum L.) cultivar Zhong Mian Suo 45 (ZMS-45) was used, the PCD processes and metabolism of reactive oxygen species were studied during the development of cotton fiber. The effects of plant growth regulators on fiber's PCD was also studied. The main results of this paper were as follows.1. DNA samples were extracted from cotton fiber cells at 9DAA, 12DAA, 15DAA, 18DAA, 21DAA, 24DAA, 27DAA, 30DAA, respectively. DNA electrophoresis revealed that it all appeared an intact strip before 24DAA. 24DAA later, all DNA samples appeared"DNA ladder", which was the characteristic of PCD. This reveals that PCD does exist during the development of cotton fiber and it occurs from 24DAA, which is just at the anaphase of cotton fiber's second cell wall synthesis.2. When treated with 2mg/L GA3 just after flowering, we found that PCD also happened at 24DAA by DNA gel electrophoresis. It indicated that low concentration of GA3 had little effect on cotton fiber's PCD. But when treated with 10mg/L GA3, we found that PCD appeared at 21DAA. It illuminated that 10mg/L GA3 brought the PCD forward for about 3d. When the concentration of GA3 was elevated to 50mg/L, although no abnormality of cotton fiber development was found before 21DAA, the DNA appeared dispersion strip by gel electrophoresis at 21DAA. It showed that high concentration of GA3 stimulated cotton fiber cell excessively, then the abnormal cell death took place.3. When treated with 1mmol/L 6-BA at the day after flowering, we found that PCD also happened at 24DAA by DNA gel electrophoresis. It illuminated that low concentration of 6-BA had little effect on cotton fiber's PCD. But when treated with 5mmol/L 6-BA, we found that PCD happened at 27DAA. It indicated that 5mmol/L 6-BA delayed the PCD of cotton fiber. After treatment with 10mmol/L 6-BA, cotton fiber developed normally before 27DAA and the DNA sample appeared dispersion strip at 27DAA. It illustrated that high concentration of 6-BA also caused an excessive stimulus to cotton fiber cell, which brought about the abnormal fiber cell death.4. During the development of cotton fiber, its soluble protein content decreased gradually. But 3 days before programmed cell death occured, the degree of falling declined. It suggested that new proteins syntheses were involved in PCD. When treated with 10mg/L GA3 and 10mmol/L 6-BA, we found that they influenced the soluble protein changing trend to cotton fiber cells, which was consistent with the tendency of PCD.5. During the development of cotton fiber cells, the SOD activity increases before 21 DAA g, and then it decreases 21 DAA later. And its MDA content always appears to increase from 9DAA to 30 DAA. The MDA content shows a much higher increase speed from 21 DAA to 24 DAA. It illustrates that PCD may be induced by the accumulation of reactive oxygen species.6. When treated with GA3, SOD activities decreased compared with control. On the contrary, MDA contents raiser to a higher level compared with the control. When treated with 10mg /L GA3, SOD activities peaked 3 days earlier, so did the MDA content, than the PCD of fiber cells. When treated with 5mol/L 6-BA, both the SOD activities decrease and the MDA contents increase peaked 3 days later, which was consistent with the delay of programmed cell death. |
