土壤鹽度及氮肥用量對水稻生育醇、生育三烯醇及γ-谷維素含量之影響

Abstract

生育醇 (Toc)、生育三烯醇 (T3) 及γ-谷維素為水稻的主要機能性成分。Toc也是植物體中重要的脂溶性抗氧化物；在氧化逆境下，其可清除植物體內過多的ROS及脂質過氧化物。本研究目的為探討不同土壤鹽度及氮肥用量對水稻及榖粒中Toc、T3及γ-谷維素含量之影響。盆栽試驗於本校人工氣候室中進行 (日溫/夜溫: 30/25℃)。氯化鈉於水稻生殖生長後期 (插秧後95天) 加入土壤中，四種處理的導電度分為0.3 (對照組, EC0.3)、2 (EC2)、4 (EC4) 及8 (EC8) dS m-1。氮肥試驗之氮肥施用量分為0N (0 g urea pot-1)、0.5N (0.25 g urea pot-1)、1N (對照組, 0.5 g urea pot-1)、2N (1.0 g urea pot-1) 及3N (1.5 g urea pot-1)，試驗設計為完全隨機排列 (CRD)。鹽分試驗結果顯示，隨土壤EC值升高，穀粒中總維生素E、總T3、α-Toc、α-T3及γ-T3濃度和對照組相比皆有顯著增加，但總Toc的濃度則無顯著差異。在高鹽度 (EC8) 處理下榖粒中γ-谷維素的濃度有顯著增加。丙二醛 (MDA) 濃度在鹽分處理下只葉片有顯著增加。隨鹽度增加，地上部與榖粒之Ascorbate (AsA) 濃度有顯著降低。氮肥試驗結果顯示，2N處理組的榖粒中總Toc、總T3、α-T3、β-Toc、γ-Toc、γ-T3及AsA濃度皆顯著比對照組高，但δ-T3則顯著較低。除0N處理外，其他氮肥處理組的γ-谷維素濃度顯著降低。在0N及0.5N處理下MDA含量皆顯著增加。本研究說明適度提升土壤鹽度可使穀粒的總維生素E與總T3的濃度增加，且不影響榖粒產量。氮肥試驗只發現在2N處理組中榖粒的總Toc及總T3、α-T3、β-Toc、γ-Toc及γ-T3濃度有明顯增加，且在0N處理下會使榖粒MDA及H2O2濃度上升，顯示缺氮可能造成榖粒無法正常生合成Toc、T3及其它抗氧化物質，導致產生氧化壓力的增加。γ-谷維素的濃度顯示必須在高鹽度與缺氮環境下才有明顯提升，此可能較不適用在實際耕作方式上。

Tocopherol (Toc), tocotrienols (T3) and γ-oryzanol are the main functional components of rice. Toc is an important lipid antioxidant in plants that can remove excessive ROS and lipid peroxides. The objective of this study was to investigate the effect of soil salinity and nitrogen fertilizer on Toc, T3 and γ-oryzanol contents in rice. The experiment was conducted on the pot culture in the artificial climate greenhouse (day/night temperature: 30/25℃). NaCl was added during the reproductive stage of rice (95 days after transplanting), the treatments were four levels of salinity with electrical conductivity of 0.3 (EC0.3), 2 (EC2), 4 (EC4) and 8 (EC8) dS m-1. The nitrogen fertilizer treatments were 0N (0 g urea pot-1), 0.5N (0.25 g urea pot-1), 1N (control, 0.5 g urea pot-1), 2N (1.0 g urea pot-1) and 3N (1.5 g urea pot-1) times of recommended application rates, they were arranged in a completetly randomized design. Results showed that compared with the control group, concentrations of total vitamin E, total T3, α-Toc, α-T3 and γ-T3 in grains increased with increasing soil salinity, however the concentration of total Toc was not affected. Under high salinity (EC8) conditions, γ-oryzanol concentration increased significantly in grains while γ-Toc decreased. Salinity treatments caused MDA concentration to increase in the leaf. The concentration of ascorbate (AsA) was noted to decrease significantly in leaf and grains while increasing salinity. Results in nitrogen fertilizer treatments showed that the concentrations of total Toc, total T3, α-T3, β-Toc, γ-Toc, γ-T3 and AsA increased significantly while the concentration of δ-T3 reduced as compared with the control. In grains, γ-oryzanol concentration was higher in 0N than other treatments. Under 0N and 0.5N treatments, MDA concentration was significantly increased. This study indicates that moderately increasing soil salinity can enhance total vitamin E and total T3 concentrations in rice grains without affecting grain yield. 2N treatment showed significant increase in total Toc and total T3 concentrations, whereas 0N treatment cause MDA and H2O2 concentrations to increase in grains; this indicates that nitrogen deficiency may reduce the biosynthesis of Toc, T3 and other antioxidants, consequently that may lead to oxidative stress. Although γ-oryzanol concentration was shown to increase in the high salinity and nitrogen deficiency conditions, the application of this farming practice to enhance its level may not be practical.