| ABSTRACT:Temperature is a key factor of circumstance and influence many aspects of agriculture. As a temperature-sensitive plant, if they were placed in 13-18℃and last for a week, tobacco will bloom earlier with lower leaf numbers than normal ones. Early blooms decrease the economic incomes of tobacco peasants for the decreased leaf number and lower quality. Researchers pay attention to early bloom for a long time. Recently, ascorbate and sucrose were reported to be involved in flowering regulation, however, their floral induction mechanism are not clear still. This paper aimed to determine the molecular mechanisms of ascorbate and sucrose in floral induction promoted by low temperature in tobacco (Nicotiana tabacum cv. K326). The main results were as follows:1. NtSOCl (GB:X76188), one of the flowering integrator genes, was cloned. And its sense and anti-sense vectors were constructed and introduced into tobacco.2. Dehydroascorbate was confirmed as a key factor to promote tobacco flowering earlier.①The contents of sucrose, ascorbic acid (AsA) and dehydroascorbate (DHA) in transgenic and wild type tobacco plants were determined, and results showed that, compared with wild type, DHA increased in early flowering transgenic plants (sense), and decreased in flowering delayed transgenic plants (anti-sense);②and in two transgenic plants, sucrose contents were similar, and AsA levels were lower than wild type both.③The transportation of sucrose and DHA were promoted from leaf to shoot apical meristem after 4℃treatment for 24 hours.④Results of semi-quality RT-PCR showed that, the expression levels of SOC1 and LFY, key genes in floral induction pathway, were increased in SAMs treated with low temperature and DHA, but almost not changed in SAMs treated with As A and sucrose. It was demonstrated that DHA was the positive factor in floral induction.⑤DPI, PD98059, cytochalasin B reversed the increased expression levels of SOC1 and LFY in SAM treated with low temperature or DHA. It proved that DHA signaling pathway was involved in the process of increasing of SOC1 and LFY in SAM induced by low temperatrure.3. NADPH oxidase in plasma membrane, calcium channel, MAPK, PTPase and DHA transporter in plasma membrane were involved in DHA signal transduction pathway. Specific inhibitors were added respectively into solutions as tobacco lower epidermis were treated with DHA, such as diphenylene iodonium (DPI), CoCl2, PD98059, phenylarsine oxide (PAO) and cytochalasin B. They inhibited the stoma closure induced by DHA, suggesting that these signal molecules were all involved in DHA signal pathway.4. DHA signal pathway contributes to tobacco root growth inhibition induced by DHA. The root length of tobacco seedling shortened along with the increase of DHA concentration. Add DPI, PAO, PD98059 or cytochalasin B respectively in DHA solution, could reverse the root growth inhibition induced by DHA. It was still found that DHA treatment for 24h induced the decrease of root activity, and increase activities and expression levels of pyruvate decarboxylase and alcohol dehydrogenase. Implicated that anoxia could also be induced by DHA in tobacco roots. |
