UV-B照射對土肉桂葉子立木活性化合物含量之影響

Abstract

地球之臭氧層日漸稀薄，使得陽光中之UV-B透過大氣層的部分逐漸提高，而植物為了減少胞器受到UV-B之傷害，會促使細胞合成更多的活性化合物累積在葉子中。這些化合物中，有些黃酮類化合物除了可吸收UV-B能量外，更可進一步清除UV-B照射所形成之自由基。此機制可使葉子產生更多活性化合物，在植物利用上具有開發之潛力。臺灣重要經濟樹種之一土肉桂（Cinnamomum osmophloeum Kanehira）葉子含有多種Kaempferol類黃酮醣苷，具有抗氧化及降低細胞血糖等作用等多種生物活性，本研究以土肉桂作為試材，測定UV-B照射後葉子化合物含量之變化。 本研究首先將土肉桂照射4 h UV-B後，採收距燈源不同距離之葉子進行萃取。試驗結果顯示，光照距離為30 cm（UV-B能量為4.20 W m-2）之組別，在照射後其總黃酮類化合物有最大增幅（1.21倍），故以30 cm為試驗光照距離。除了照射4 h UV-B外亦測試不同光源之光照順序，其中僅有照射2 h藍光接續2 h UV-B組別之總黃酮類化合物含量有顯著的增加，為照射前的1.18倍，與照射4 h UV-B組別之總黃酮類化合物含量增加結果相近。 為測試單日光照中土肉桂葉子之活性化合物最大改變倍率，因此改變UV-B照射時數為2、4、6及8 h，測得照射4 h及8 h UV-B時會有較高的單日總黃酮類化合物增加倍率，其中照射4 h UV-B結果較佳。此外，也對土肉桂葉子水可溶部中主要的5種黃酮類化合物之改變倍率進行測試，包含Kaempferol-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-7-O-α-L-rhamnopyranoside（F1）、Kaempferol-3-O-β-D-apiofuranosyl-(1→2)-α-L -arabinofuranosyl-7-O-α-L-rhamnopyranoside（F2）、Kaempferitrin（F3）、Kaempferol-3-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinofuranosyl-7-O-α-L -rhamnopyranoside（F4）及Kaempferol-3-O-α-L-rhamnopyranoside（F5）。試驗結果顯示，照射UV-B時數對F1-F5化合物改變倍率並無顯著影響。因此，後續試驗條件仍為照射4 h UV-B。 更進一步將單日照射4 h UV-B之過程重複2、4及8 d，結果顯示，照射4 d UV-B時總黃酮類化合物改變倍率會更進一步增加為1.39倍，但與照射8 d UV-B組別之增加倍率沒有顯著差異。至於總酚類化合物，則是於照射4 d UV-B之組別增加為1.20倍，延長照射時間為8 d UV-B後，總酚類化合物顯著增為1.37倍。水可溶部5種化合物F1-F5照射後之改變倍率也與總黃酮類化合物試驗結果相似。照射4 d UV-B後F1、F2及F3化合物皆顯著增為約1.42倍，但照射4 d UV-B卻與照射8 d組別之增加倍率沒有顯著差異。 綜合所有結果顯示，無論是總黃酮類化合物、總酚類化合物及水可溶部黃酮醣苷之含量，皆顯示距離燈源30 cm時，照射4 h UV-B連續4 d是最有效率的增加化合物含量之照射條件。此條件下，照射後總黃酮類化合物增為1.39倍、總酚類化合物增為1.20倍、化合物F1、F2及F3可增為照射前之1.42倍。

The depletion of ozone in the atmosphere has resulted in an increase in UV-B irradiation. A high UV-B dosage provokes damage to organism. Plants may attenuate the impact of UV-B irradiation through the accumulation of different types of phenolics produced. Most of these compounds are flavonoid, which can act as an effective UV-B screen. Moreover, some flavonoids may also eliminate free radicals which caused by UV-B radiation. This mechanism will make leaves to synthesis more active compounds, which can be used potentially. Cinnamomum osmophloeum is one of the indigenous trees in Taiwan. This tree contains aboundant kaempferol glycoside compounds in its leaves. These compounds were proved to have antioxidant activity and hypoglycemic effect. This study would irradiate C. osmophloeum leaves with UV-B in various conditions to test the variations of activity compound contents in the leaves. First, we irradiate leaves with 4 h UV-B by different irradiation distances, and the changing ratio of the total flavonoid contents increase to the maximum 1.21 fold when irradiated at 30 cm (UV-B energy: 4.20 W m-2). We decided to use 30 cm as the irradiation distance for all other tests. Besides, we change 4 h UV-B irradiation to different order of different light irradiation. Only the test group of 2 h blue light + 2 h UV-B showed increased total flavonoid content ratio to 1.18 fold which is similar to the result when trees irradiated with UV-B for 4 h. Furthermore, in order to know the maximum changing ratios of the active compounds per day, we treat C. osmophloeum leaves with 2, 4, 6 and 8 h irradiation. The changing ratios of the total flavonoid contents were better when irradiating with 4 or 8 h UV-B per day, with the best result when irradiating UV-B for 4 h. Furthermore, in investigating the changing ratio from the UV-B irradiation of the 5 major flavonoid compound, kaempferol-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl -7-O-α-L-rhamnopyranoside (F1), kaempferol-3-O-β-D-apiofuranosyl-(1→2)-α-L -arabinofuranosyl-7-O-α-L-rhamnopyranoside (F2), kaempferitrin (F3), kaempferol-3-O-α-L-rhamnopyranosyl-(1→2)-α-L-arabinofuranosyl-7-O-α-L -rhamnopyranoside (F4) and kaempferol-3-O-α-L-rhamnopyranoside (F5) in the water soluble fraction of C. osmophloeum leaves, the results showed that there were no significant differences between the changing ratios of compound F1-F5 from the irradiation with different hours of UV-B. As the result, we decided to treat leaves with 4 h UV-B irradiation as the continuous irradiation condition. When the trees continuously irradiated UV-B for 4 h per day and lasted for 2, 4 and 8 d, the changing ratios of total flavonoid contents would significantly increase to 1.39 fold after irradiated UV-B for 4 d. But the result for irradiation for 4 d has no difference to that of irradiation UV-B for 8 d. The changing ratio of the total phenolic contents is significantly increased to 1.20 fold when irradiating UV-B for 4 d. Besides, when the tree irradiatind UV-B for 8 d, the changing ratio of total phenolic contents has significant increased to 1.37 fold. The 5 compounds, F1-F5, in the water fraction showed similar changing ratios to that of the total flavonoid contents. The changing ratios of compound F1, F2 and F3 would increase to 1.42 fold after irradiated UV-B for 4 d, but the result for irradiation for 4 d has no difference to that of 8 d. As the result, we have concluded that to increase total flavonoid contents, total phenolic contents and the flavonol glycoside form water fraction, the most effective condition is to irradiate trees with UV-B at a 30 cm diatance for 4 h per day and last for 4 d. The total flavonoid contents would increase to 1.39 fold, the total phenolic contents would increase to 1.20 fold, the compound F1, F2 and F3 would increase to 1.42 fold when irradiating with this condition.