水稻幼苗根氯化鈉逆境之研究：過氧化氫之功能

Abstract

本論文係以水稻品種台中在來一號(Oryza sativa L. cv. Taichung Native 1)黃化幼苗作為材料，探討(a)過氧化氫(H2O2)與氯化鈉(NaCl)所抑制水稻黃化幼苗根生長之關係、(b) H2O2與NaCl誘導水稻黃化幼苗根穀胱甘肽還原酶(glutathione reductase, GR)活性增加之關係及(c) NaCl逆境下水稻黃化幼苗根H2O2和血紅素氧化酶(heme oxygenase, HO)活性之關係。 NaCl抑制水稻黃化幼苗根之根長及根乾重，在相同滲透勢條件下，NaCl與NaNO3對水稻黃化幼苗根長及乾重抑制情形相同，然而mannitol的抑制較為減緩。NaCl使幼苗根中於3小時迅速累積H2O2，發生在NaCl抑制幼苗根生長(6小時)前。Ascorbic acid (AsA) 、diphenyleneiodonium (DPI) 、imidazole (IMD) 及sodium nitroprusside (SNP)皆可降低NaCl所誘導根中H2O2累積，卻無法回復根長及乾重之降低，證實水稻黃化幼苗在NaCl逆境下，因Na+之作用透過細胞膜上之NADPH oxidase形成H2O2，然而H2O2並非NaCl抑制水稻黃化幼苗根生長之限制因子。 NaCl誘導水稻黃化幼苗根中GR活性之增加，且H2O2累積與GR活性提升均發 生於NaCl處理3小時後。AsA、DPI、IMD及SNP皆可以降低NaCl所導致根中H2O2 累積與GR活性增加。NaCl亦可增加水稻黃化幼苗根中HO活性，且NaCl所誘導之 HO活性提升(6小時)在H2O2累積(3小時)後。AsA、DPI、IMD及SNP可清除NaCl 所導致之H2O2累積，同時降低NaCl所誘導之HO活性提升。外加H2O2可使水稻幼 苗根GR及HO活性提升。另外，NaCl與NaNO3造成GR及HO活性之提升相同。本 論文之結果證實NaCl透過Na+作用以H2O2做為訊息分子誘導水稻黃化幼苗根中 GR及HO活性提升。

In this thesis, rice (Oryza sativa L. cv. Taichung Native 1) etiolated seedlings were used to investigate (a) the role of H2O2 in NaCl-inibited growth of rice etiolated seedling roots, (b) the role of H2O2 in NaCl-increased glutathione reductase(GR)activity of rice etiolated seedling roots, (c) and the role of H2O2 in NaCl-increased heme oxygenase activity of rice etiolated seedling roots. Rice etiolated seedlings treated with NaCl increased H2O2 production in rice roots (3 hours), and then inhibited root growth of etiolated seedlings (6 hours). Addition of H2O2 scavenger ascorbic acid (AsA) and nitric oxide (NO) donor sodium nitroprusside(SNP) , which decreased H2O2 accumulation, could not reduce NaCl-inhibited growth in rice roots. Also, application of NADPH oxidase inhibitors diphenyleneiodonium(DPI) and imidazole(IMD), which inhibited the H2O2 production, had no effect on NaCl-inhibited root growth. These data indicated that H2O2 production through NADPH oxidase caused by Na+ is unlikely responsible for NaCl-inhibited root growth. NaCl treatment increased H2O2 production and GR activity in rice roots. Addition of AsA and SNP, which decreased H2O2 accumulation, could lower the NaCl-induced GR activity. Also, application of DPI and IMD, which inhibited the H2O2 production, reduced the NaCl-induced GR activity. NaCl treatment resulted in an increase in HO activity in roots of rice etiolated seedlings. Results of time-course study indicated that H2O2 accumulation occurred 3 hours after NaCl treatment, whereas the increase in HO activity occurred 6 hours after NaCl treatment. Addition of AsA and SNP, which decreased H2O2 accumulation, could lower the NaCl-induced HO activity in rice etiolated seedling roots. Also, application of DPI and IMD reduced the NaCl-induced HO activity. Moreover, NaNO3 and NaCl are equally effective in inducing GR and HO activity, indicating that Na+ but not Cl- is responsible for increasing GR and HO activities. Based on the data of this thesis, it is concluded that H2O2 production caused by NaCl may be responsible for NaCl-increased GR and HO activities in rice etiolated seedling roots.