短波紫外線誘導椪柑及柳橙果實中Scoparone之生成

Ultraviolet-C Induced Scoparone Synthesis in 'Ponkan' Mandarin (Citrus reticulata Blanco) and 'Liucheng' Orange (Citrus sinensis Osbeck) Fruit

本試驗以0.5-3.0 KJ／平方公尺問不同劑量之短波紫外線（UVC，254 nm）照射椪柑（Citrus reticulata Blanco）及柳橙（Citrus sinensis Osbeck）果實後，測定其誘導產生之植物殺菌素－－scoparone之生成及含量變化。椪柑及柳橙果實經UVC照射後之果皮萃取物，經由薄層色層分析（TLC）及高效液相層析（HPLC）二種方法分析，均可測得有scoparone之生成；但另一種植物殺菌素－－scopoletin則僅有極少量之生成。誘導生成之scoparone大部份存在於直接受到UVC照射之果皮部分，而且主要之生成部位是外果皮（油胞層）。照射後之果實在15℃中貯藏，果皮中之scoparone含量逐漸增加，至10天左右達最高量，然後又逐漸下降。較高之照射劑量可誘導椪柑生成較多之scoparone，但對早採之柳橙卻無此效果。以相同劑量UVC照射椪柑及柳橙果實，椪柑中scoparone之生成量高於柳橙。不同時期採收之椪柑對UV-C之反應無明顯差異，但晚採之柳橙所誘導生成之scoparone明顯較早採收者為低。以1.5及3.0KJ／平方公尺UV-C照射會引起柳橙果皮出現疑似受傷之紅斑，但未引起椪柑果皮傷害。 The induction of phytoalexins-scoparone (6, 7-dimethoxycoumarin) and scopoletin (6-methoxy, 7-hydroxycoumarin) in the pericarps of 'Ponkan' mandarin (Citrus reticulata Blanco) and 'Liucheng' orange (C. sinensis Osbeck) by short wavelength ultraviolet light irradiation was studied. Citrus fruits were irradiated with 254 nm ultraviolet light (UVC) at dosages ranging from 0.5 to 3.0 KJ/m^2. The formation of scoparone in peel extracts of irradiated fruits were identified by both thinlayer chromatography (TLC) and high performance liquid chromatography (HPLC). The formation of scopoletin were insignificant. Most of the UV-C induced scoparone was found in the part of peel that was exposed to UV light directly, and it was located mainly in the flavedo (exocarp) tissue of the irradiated fruit. After irradiation, at 15℃, scoparone concentration increased rapidly and reached its peak value around 10 days and began to decline thereafter. Higher dosage induced higher scoparone synthesis in 'Ponkan' mandarin, however same effect was not found in earlypicked 'Liucheng' orange. At the same dosage, more scoparone was induced in 'Ponkan' mandarin than in 'Liucheng' orange. There were no apparent differences among 'Ponkan' mandarins harvested at different dates toward UVC treatment, but lateharvested 'Liucheng' orange showed lower scoparone synthesis as compared to the earlyharvested fruit. 'Liucheng' orange developed tiny red dots on the skin after irradiation with 1.5 and 3.0KJ/m^2 UVC. On the other hand, 'Ponkan' mandarin had no signs of skin damage after irradiation at the same level.