摘要或動機

植物依靠向光性爭取最多的光線，以進行光合作用，製造食物供給所有生物。雖然在十九世紀時植物的向光性就已經被發現，並且參與植物向光性的主要荷爾蒙為植物生長素也已經熟知，但是主要是植物的哪一個組織接受光訊息以誘導向光性，以及細胞內的哪些分子參與訊息傳遞，則都不清楚。因此這個研究，以可以發射特殊波長的發光二極體為光源照射綠豆小苗以研究向光性，結果顯示藍光和綠光而不是紅和黃光可以誘導向光性。就向光性訊息傳導的組織層面的研究而言，將豆苗的葉、葉柄、生長點、子葉分別除去後，再側面照光，發現向光性要產生必須要有生長點或葉柄，並且發現莖可以誘導向光性，而葉子不能誘導向光性，因此莖是主要接受光訊息以誘導向光性的組織。就向光性訊息傳導的分子層面的研究而言，植物以鈣離子的螯合劑和鈣離子通道阻斷劑處理後發現，細胞質內鈣離子濃度的增加是藍光和綠光誘導的向光性所需要的過程，有趣的是藍光誘導向光性的訊息傳導過程中，除了經由細胞內的鈣離子濃度的增加外，還有其它鈣離子不參與的訊息傳導途徑。此外，以蛋白質磷酸?抑制劑和蛋白質去磷酸?抑制劑處理植物後發現，藍光和綠光所誘導的向光性訊息傳導，都包含蛋白質去磷酸?第1 和2a 型在細胞內的作用。因此植物的向光性需要有生長素才會表現，生長素由生長點製造後由生長點和葉柄儲存，在光刺激之下會誘導莖產生傳遞訊息，此訊息會傳遞到含有生長素的生長點和葉柄，使得生長素流向照光組織細胞，並且使得細胞內鈣離子濃度增加，活化蛋白質去磷酸?第1 和2a 型，進而造成植物的向光性。Phototropism allows plants to receive the most amount of light to perform photosynthesis, which produces food and energy for all organisms. The phenomenon of phototropism has been known since the 19th century, and auxin has been identified to be the main hormone involving in phototropism. However, the major plant tissue responsible for receiving light signal is not fully understood, and the signal transduction pathway within cells after light activation is not clear. Therefore, the phototropism of mungbean seedlings is examined by Light Emitting Diodes (LED) which produce the specific wavelength of light in this study. Results point out that blue and green lights rather than red and yellow lights induce phototropism of moonbeam. The phototropism of mungbean seedlings is further studied by plants whose leaves, petioles, apical meristem, or cotyledons were removed, showing that the presence of either apical meristem or petioles is needed for inducing phototropism. Also, stem ,not leaves, is the major tissue that receives light activation, and induces phototropism. The signal transduction of phototropism was further analyzed in the presence of calcium ion chelator and channel blockers. The signal transduction of phototropism induced by blue or green light contains the increasing concentration of calcium ion within cytosol. Interestingly, there is a calcium-independent tansduction pathway for blue light only to induce phototropism. Additionally, staurosporine (STA), a protein kinase inhibitor and okadaic acid (OKA), a protein phosphatase inhibitor, were used to study the signal transduction pathway of phototropism, and results indicated that protein phosphatase 1 and 2a is needed for both blue and green lights to induce phototropism. Conclusively, the phototropism is triggered by the reception of light by stem, and the light signal is transferred to apical meristem and petioles that reserve auxin produced from apical meristem. Auxin is then transferred to the cells that is illuminated, increases the concentration of calcium ion and activates protein phosphatase 1 and 2a in cells, and finally phototropism occurs.