乙烯誘導芥藍葉片老化過程中之抗氧化反應

Antioxidant Responses in Ethylene-induced Leaf Senescence of Chinese Kale (Brassica oleracea L. Alboglabra Group)

本試驗以對乙烯敏感的‘蕙津’芥藍（Brassica oleracea L. Alboglabra Group cv. 'Veg Gin'）3週苗齡的第二片本葉之切離葉片為試驗材料，研究乙烯促進切離葉片老化時抗氧化酶的反應，以及乙烯所促進的葉片老化是否與氧化逆境有關。芥藍幼苗第二片本葉切離後在25℃黑暗中以1ppm乙烯處理4天，明顯加速葉片黃化。乙烯處理第3天葉片中之葉綠素與蛋白質含量顯著低於對照（空氣）組。過氧化氫（H2O2）與丙二醛（malondialdehyde, MDA）含量在乙烯處理第1、2天開始增加，並高於對照組。葉片的抗氧化防禦系統中的ascorbate peroxidase（APX）、glutathione reductase（GR）與peroxidase（POX）等抗氧化酵素的比活性在乙烯處理2天後顯著增加，但superoxide dismutase（SOD）與catalase（CAT）則無顯著變化。此結果表示，乙烯連續處理誘導芥藍切離葉片開始老化，是由於乙烯促使內生H2O2含量的增加，造成脂質過氧化作用程度加劇，導致MDA含量的累積；在引起葉片氧化逆境增加時，APX、GR與POX等抗氧化酵素也被誘導增加。 The purpose of this research was to study the changes in enzyme activities of antioxidant system in excised leaves in response to ethylene, and to find out the relationship between oxidative stress and ethylene-induced leaf senescence. Plant material used in this study were the second fully developed leaf of3-weekold seedlings of the ethylene-sensitive 'Veg Gin' Chinese kale (Brassica oleracea L. Alboglabra Group). Incubating the excised leaves of Chinese kale in dark at 25℃ in the presence of 1ppm ethylene for 4 days greatly accelerated the process of leaf yellowing. The ethylene treated leaves, in comparison with the air-treated control, had significantly lower chlorophyll and protein content on the third day. The hydrogen peroxide (H2O2) and malondialdehyde (MDA) content started to increase on the 1(superscript st) and 2(superscript nd) day after ethylene treatment, and were much higher than the control. Specific activities of three antioxidant enzymes within the plant's antioxidant defense system: the ascorbate peroxidase (APX), the glutathione reductase (GR) and the peroxidase (POX), all showed significant increase after two days in the ethylene-treated leaves. On the other hand, the superoxide dismutase (SOD) and the catalase (CAT) changed very little in these leaves. The above results suggested that in excised leaves of Chinese kale, ethylene induced their rapid senescence first by an increase in H2O2, which caused an increase in the lipid peroxidation of the membrane systems and resulted in the accumulation of MDA. When the oxidative stress progressed, enzymes in the cellular antioxidant system including APX, GR and POX responded by increasing their specific activities.