| Summary: | 碩士 === 國立成功大學 === 生命科學系碩博士班 === 98 === The common way to induce spiking of Phalaenopsis is by low temperature treatment. Although we know it flowers under low temperature treatment, the detail mechanism is still unknown. In 2008, Chen et al. reported that cool-night temperature not only induces spike emergence but also increase free sugars in Phalaenopsis aphrodite. Based on this, we proposed to answer both why sucrose content elevates and why Phalaenopsis starts spiking under cool-night temperature. First, we analyzed the expression level of three sucrose synthase genes, three invertase genes and one sucrose phosphate synthase gene. By using quantitative real-time RT-PCR, our results showed that PaINV1, PaSUS1 and PaSUS6 showed decrease in their expression, while the rest four genes were not strongly correlated to the elevated sucrose content. In plant cell, sucrose is not only a nutrient but also a signaling molecule. We hypothesized that sucrose may play a key role via SnRK1 signaling. Interestingly, we found that the kinase activity of PaSnRK1 reduced during cool-night temperature although its mRNA expression remained unaffected. This implied that PaSnRK1 is involved in the flowering process of Phalaenopsis aphrodite. Secondly, we analyzed the expression levels of ten flowering genes from four flowering pathways by using quantitative real-time RT-PCR. We found that autonomous pathway genes (PaFCA and PaFPA) and photoperiod pathway genes (PaGI and PaFT) were upregulated under cool-night treatment, while vernalization pathway genes (PaVIN3-1, PaVIN3-2 and PaVRN) were not significantly affected. This indicated that autonomous and photoperiod pathways were two major pathways in the cool-night induced flowering process of Phalaenopsis. Finally, we proposed that cool-night temperature increases the level of sucrose that reduces the kinase activity of the PaSnRK1, and the down-regulated PaSnRK1 transfers its signal to unidentified downstream targets and then affects the flowering gene expression that eventually induces flowering of Phalaenopsis.
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