不同水稻品種鐵膜對三價砷與五價砷於水稻幼苗植體中累積及其物種之影響

Abstract

本研究選用兩個不同鐵膜生成量之水稻品種，以水耕試驗探討鐵膜對As(III) 與As(V) 於水稻幼苗植體中物種及其累積之影響。先將水稻幼苗種植於額外添加 0 及 30 mg Fe(II) L-1 之木村氏B水耕液中三天，使台稉九號與台中在來一號根部表面生成紅棕色之鐵膜後以半強度木村氏B水耕液種植一天，接著將水稻換至含有0、0.5 及1 mg L-1 之As(III) 或 As(V) 養液中，種植14天後採收。採收後植體分為地上部與根部，分別測量株高、根長及鮮重，取部分根部樣品以dithionite-citrate-bicarbonate溶液溶解鐵膜，並分析剩餘根部及地上部樣品之砷、鐵、磷及砷物種濃度。結果顯示，Fe(II)、As(V) 及As(III) 皆會對水稻造成毒害，又以台稉九號對 Fe(II) 及As(III) 的耐受性較台中在來一號高。相較於As(III) 處理組，在As(V) 處理下，鐵膜可吸持較多含量之砷於根表面。由鐵膜上之砷/鐵莫耳比結果可知，不同水稻品種鐵膜對不同型態砷之吸持能力有差異(P < 0.05)，即使台稉九號生成之鐵膜量顯著高於台中在來一號，台中在來一號生成之鐵膜在As(III) 或As(V) 處理下砷鐵之莫耳比值皆較台稉九號高，顯示其對砷之吸持能力較台稉九號強，推測可能為鐵膜生成之鐵(氫)氧化物型態不同所致。此外，在未添加 30 mg Fe(II) L-1 處理中，兩個水稻品種不論以As(III) 或As(V) 處理，植體地上部砷總量之 77-98 % 為As(III)，因水稻具有砷酸還原酶，可將As(V) 還原成As(III)。在 30 mg Fe(II) L-1 處理下之所有砷處理水稻地上部As(V) 比例顯著增加，水稻受砷毒害效應減緩，推測因 Fe(II) 毒害造成水稻氧化壓力提高，使得As(V) 比例增加，且因As(V) 對水稻毒性較As(III) 低，因而減緩砷對水稻的毒害。

In the present study, two contrast rice (Oryza sativa L.) cultivars, high iron plaque cultivar Taikeng 9 (TK9) and low iron plaque cultivar Taichung Native 1 (TCN1), with different capability of forming iron plaque were selected for hydroponic experiments to investigate the effect of iron plaque on As(III) and As(V) uptake and transformation in rice plants. Two-week-old rice seedlings were placed in Kimura B nutrient solutions with additional 30 mg L-1 Fe(II) as FeSO4．7H2O or without Fe(II) for 3 days to form iron plaque. After iron plaque formation, seedlings were transplanted in half-strength Kimura B nutrient solution overnight and then exposed to different As concentrations for 14 days. The treatments included: (1) control (2) 0.5 mg As(III) L-1 (3) 1.0 mg As(III) L-1 (4) 0.5 mg As(V) L-1 (5) 1.0 mg As(V) L-1. The results indicated that TK9 showed higher tolerance to As(III) and Fe(II) toxicity as compared to TCN1. More As adsorbed by iron plaque was observed by As(V) treatment in both genotypes. According to As/Fe molar ratio of iron plaque, TCN1 showed higher As sorption ability than TK9. It suggested that the species of iron oxyhydroxides may be an important factor on As sorption affinity. The main As species accumulated in rice shoots was As(III) (over 70%) regardless exposure to As(III) or As(V). In this study, iron plaque had no significant effect on short-term As uptake for TK9 and TCN1, except for TK9 treated with As(V). However, after Fe(II) treatment, the proportion of As(V) species in shoots for all As treatments and genotypes were significantly increased, and which could reduce the As toxicity to rice plants. It might result from that Fe(II) application could induce higher oxidative capacity of rice roots, which then caused As(III) to be oxidized As(V) and increasing proportion of As(V) in rice shoots.