本論文主要探討離層酸 (abscisic acid，ABA) 促進水稻台中在來一號 (Oryza sativa L. cv. Taichung Native 1, TCN1) 三葉齡幼苗葉片老化之生理反應。老化葉片中malondialdehyde (MDA)、H2O2 (hydrogen peroxide) 和GSSG (oxidized glutathione) 增加，ASC (reduced ascorbate) 減少，但抗氧化酵素GR (glutathione reductase)、APX (ascorbate peroxidase) 比活性會有所提高，顯示葉片老化的原因可能為氧化逆境的產生。而在氮素代謝方面，ABA處理會促進蛋白酶 (protease) 活性與比活性，造成第二葉游離銨根 (NH4+) 增加。Glutamine synthase活性降低，但NADH-Glutamine dehydrogenase 和NADP-isocitrate dehydrogenase 活性抑制程度則較不明顯，顯示ABA主要是透過抑制GS活性進而促使葉片老化。此外，ABA 能誘導葉片澱粉提早降解而使游離醣類增加，並促使 HXK (hexokinase)活性和比活性增加，顯示葉片老化與醣類訊號相關。這些結果說明ABA會誘導氧化逆境產生並干擾氮素和醣類代謝促使葉片老化。 Abstract Rice (Oryza sativa L., cv. Taichung Native 1, TCN1) seedlings were used to investigate the abscisic acid-induced leaf senescence. Increased MDA (malondialdehyde), H2O2 (hydrogen peroxide), GSSG (oxidized glutathione) contents and reduced ASC (ascorbate) contents were observed in senescenced leaves. Activities of antioxidant enzymes such as GR (glutathione reductase) and APX (ascorbate peroxidase) were induced in senescence leaves. These data suggest that the ABA induced leaves senescence may cause from oxidative stress. Furthemore, ABA also induced protease activity and increased ammonia ions concentration. In contrast, glutamine synthase (GS) activity was reduced in senescenced leaves. But the NADH‐GDH (NADH-glutamine dehydrogenase) and NADP‐ICDH (NADP-isocitrate dehydrogenase) activities were unaffected. It shows that ABA mainly repressed the GS activity rather than inhibited NADH‐GDH GDH and NADP‐ICDH activity. Besides, ABA accelerated the starch degradations and increased the soluble sugars contents in senescence leaves, and induced HXK (hexokinase) activity. These results indicated that abscisic acid-induced senescence of leaves may due to oxidative stress and unbalances between nitrogen and sugars metabolism.