| Flowering is a critical growth transition point during plant's growth and development. It can be divided into four sequential processes: flowering induction, signal transduction, flowering evocation and floral organ formation. The process from flower induction to flower evocation have being the focus of research. It has been established the existence of a few pathways controlling flowering of plants in genetic research of flowering of Arabidopsis thaliana and Antirrhinum majus. Many genes related to flowering have been identified and cloned, but the regulation mechanism of gene's expression is still unclear. Research in recent years showed that DNA methylation play a role in regulating gene expression, but the assay on relationship between DNA methylation and flowering were mainly focused on model plants such as Arabidopsis. Non-heading Chinese cabbage (Brassica campestris L. ssp chinensis Makino ), a specific vegetable in China, plays important role in ensuring annual vegetable supplication. It is a facultative long-day plants. The present paper studied the variation of DNA methylation level in different developmental stage and different organs of non-heading Chinese cabbage. Germinated seeds and seedlings of non-heading Chinese cabbage were treated with 5-azacytidine (5-azaC) (demethylating agent) combined with cold and gibberillin (GA). The assay analyzed the relationship between flowering and low temperature, GA and DNA methylation and their interrelation. All the results obtained are summarized below.1. Low temperature, 5-azaC and gibberillin all promoted flowering of non-heading Chinese cabbage.Both germinating seeds and seedlings of variety Youdonger can be induced to flowering after 10-30 days at either 4癈 or 8癈. The lower the temperature was, and the longer the treatment duration was, the bigger the plant treated was, the better the promoting effects were. For variety Siyueman seeds or seedlings treated at 4癈 for 30 days did not induced to flowering, indicating strong winter variety needs lower temperature and longer duration exposed to low temperature.5-azacytidine in low concentration promoted flowering of variety Youdonger but inhibited flowering of it in high concentration. The optimum concentration were 250ujnol/L. Treatment for 10 days with low concentration 5-azacytidine combined with 4 "Ccold treatment is more effective than treatment alone, which indicated that the effects of vernalization and 5-azaC is addictive.Gibberillin of 50-300mg/L promoted flowering of young seedlings and adult plants in cv. Youdonger and the most effective concentration was 300 mg/L. Variety Siyueman needed high concentration of GA to promote its flowering, because low concentration ofGA had no any effect on its flowering. The optimum concentration of GA was 500 mg/L, in addition Siyueman needed more times of spry with GA. The results implied strong winter variety needed high amount of GA.2. Low temperature, GA and 5-azaC all can decreased the methylation level of DNA in plants. The level of 5-metylcytosine in DNA of germinating seeds and seedlings deceased 28.46% and 16.66% respectively, compared to control after cold treatment. In seeds treated with 5-azaC in various concentration the level of 5-metylcytosine in DNA decreased about 45% but there is no difference among the treatments. The level of 5-metylcytosine in DNA of plant decreased 14.52% compared to control after treatment with GA of 300mg/L.Gibberillin content of shoot apices in plant was 5 times higher than that of control after GA treatment. Cold treatment promoted synthesis of endogenous GA. The content of GA in seedlings at cotyledon stage, shoot apices and leaves of seedlings were 4 times, 2.5 times and 170% as much as control after cold treatment. However treatment with 5-azaC declined the content of GA. The content of GA in seedlings is 50% of the control after treatment with 100 umol/L of 5-azaC.The changes of protein content in shoot apices and leaves was not obvious after seedling cold-treatment. But germinating seeds d...
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