綠豆幼苗於葉片脫水狀況下抗氧化系統之變化

Changes of Antioxidative System in Mungbean Seedlings in Response to Leaf Dehydration

本文探討綠豆幼苗於離水處理後，葉片脫水之狀況下，其與活性氧族化合物去除有關之抗氧化系統之變化。綠豆幼苗在離水處理時間之前10天其葉片脫水並不嚴重，且其速率極為緩慢，但自第10天以後，葉片相對含水量極劇下降，而造成葉片有明顯萎凋情形。在離水處理之過程中，綠豆幼苗葉片葉綠素含量之減低情形，與葉片之MDA含量有密切關連。葉片抗氧化酵素活性包括SOD、CAT及APX酵素活性在葉片相對含水量低於87%時開始增加，而於葉片相對含水量為56%時達到最高點。於試驗之過程AsA總量均維持於低濃度之狀態，但是AsAIDAsA之比例只在當葉片相對含水量為56%時，有較對照組略高之清形，但不明顯。GR活性自綠豆幼苗開始受離水處理即開始增加，而於葉片相對含水量為56%時最高。Glutathione的總量及GSH/GSSG之比例，處理組在試驗過程均較對照組為高。本研究結果顯示可能綠豆幼苗於離水處理所造成葉片脫水，所衍生之可能的氧化逆境耐受性與還原態的glutathione及GR活性有關。

Changes in the antioxidative system involved in the detoxification of active oxygen species in mungbean seedlings in response to leaf dehydration were studied. The rate of leaf water loss was very slow during the first IO days of a draining treatment but because dramatic after IO days of draining and caused apparent wilting in mungbean seedlings. Reduction in chlorophyll content was closely associated with the increase in the level of lipid peroxidation, as estimated by malondialdehyde content. The activities of antioxidative enzymes including superoxide dismutase, catalase, and ascorbate peroxidase did not increase until leaf relative water content decreased below 87%. Antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) had the highest activities when leaf relative water content reached 56%. During the course of the experiment, a lower total amount of ascorbate was found in drained mungbean seedlings. It was not until the last day of treatment, when leaf relative water content reached 56%, that the AsA/DAsA ratio showed a slightly higher level in drained seedlings, compared to control seedlings Under draining conditions, activities of glutathione reductase (GR) increased from the beginning of treatment and reached to its highest level when leaf relative water content was 56%. Moreover, both total glutathione and the GSH/GSSG ratio showed a higher level in drained seedlings than in control seedlings over time. These results suggested that protection from oxidative damage by a higher level of reduced glutathione and active glutathione reductase are the key factors in an acclimation mechanism in dehydrated mungbean leaves under draining conditions before irreversible wilting occur.