在高等植物的生長發育過程中，決定由營養時期轉變為繁殖時期是一個非常重要的步驟。為了能夠讓後代在最適合的環境下生長，植物必須根據周圍環境的變遷來調節它們的由營養時期轉變為繁殖時期的過程。由經典的嫁接實驗發現，植物在接收到日照長短的改變之後，開花激素（刺激開花的物質），會在葉部生成，並且經由韌皮部長距離移動到植物頂端而誘導開花。先前的研究已經發現FLOWERING LOCUS T (FT)的蛋白質可在阿拉伯芥以及稻米中扮演類開花激素的角色。然而，當FT 蛋白質與其結合物形成複合體而侷限在維管束內時，植物開花的時間並沒有因此而延遲，顯示可能有其他扮演類開花激素的物質誘導開花的起始，推測FT 的訊息核醣核酸可能扮演誘導功能。因此，在本研究當中，利用反轉錄聚合酶鏈反應，我們首先確定了FT 的訊息核醣核酸的確存在於Brassica oleracea（一種和阿拉伯芥相當接近的物種）的韌皮部汁液中。藉著阿拉伯芥的嫁接實驗更進一步的確認了FT 訊息核醣核酸的長距離移動。本研究結果顯示，除了已被報導不具長距離移動能力的FT-EGFP 片段之外，帶著標定片段的FT 訊息核醣核酸，確實可以移動穿越嫁接的單元而被偵測到。除此之外，FT 訊息核醣核酸長距離移動和促進開花之間有正相關的關係。綜合以上，我們提出FT 的訊息核醣核酸和蛋白質可並行扮演開花激素而調節開花的時間。 In higher plants, the determination of the transition from vegetative to reproductive stage is one of the most important steps during their developmental courses. In order to produce offspring at optimal environmental conditions, plants must response to the variations of ambient condition and adjust their reproductive transition. From classic grafting experiments, it has been established that after plants receiving day-length difference, florigen, the floral stimuli, are synthesized in the leaves and then transported long-distance through phloem to trigger flowering at apices. Previous studies have shown that the protein of FLOWERING LOCUS T (FT) may act as a florigen-like molecule in Arabidopsis and rice. However, while FT protein movement is restricted by expressing a strong FT-binding protein in vascular tissues, the flowering time is not delayed, suggesting that other florigen-like molecule, probably FT mRNA, may act redundantly to trigger floral initiation. To test this possibility, we first determined the existence of FT mRNA in the phloem sap. By using RT-PCR analysis, FT mRNA is detected in the phloem sap collected from Brassica oleracea, a species closely related to Arabidopsis. To further test the long-distance movement of FT mRNA, the Arabidopsis grafting experiments were conducted. Our results show that the chimeric FT mRNA except FT-EGFP can move long-distance trough grafting unit. In addition, the detection of FT mRNA in the scion apices is well correlated with the floral promotion in the scions. Taken together, we propose that both FT mRNA and protein may act redundantly as florigens to regulate flowering time.
