【摘要】 用黄瓜为材料 ,研究了草酸对植物根切段还原Fe(Ⅲ )EDTA的促进作用。在 2～ 14mmol/L范围内随着草酸浓度的加大 ,其促进作用不断提高 ;在 4h内随着反应时间的推移 ,Fe(Ⅲ )EDTA的还原量成线性上升趋势。进一步用完整根、粗酶提取液和提纯的质膜证明 :促进作用并非草酸本身作为电子供体直接或间接地加速了铁还原反应 ,而是形成的草酸铁螯合态是根中铁还原酶更有效的底物。整体根还原草酸铁的活力和质膜铁还原酶催化草酸铁的效率 (Vmax/Km)都远大于还原柠檬酸铁和Fe (Ⅲ )EDTA的活力和效率更多还原

【Abstract】 The paper reports the enhancing effect of oxalate on Fe(Ⅲ)EDTA reduction and its mechanism in plant roots by using cucumber as material. The enhancement could be strengthened with an increase in oxalate concentration and with reaction time prolongation as well (Fig.1A, B). The first possibility is the action of oxalate as an electron donor directly or indirectly through the mediation by NAD/NADH. This is ruled out by the finding that (Ⅰ) only a high enough concentration of oxalate(> 2 mmol/L ) was effective in producing an enhancing effect (Fig.1A); (Ⅱ) ferric iron could not be reduced when oxalate or oxalate plus NAD was incubated with Fe(Ⅲ)EDTA in the presence of crude enzyme, but could be when oxalate plus NADH was used. Strong evidence,however,was obtained to support the second guess that oxalate first competed with EDTA for Fe 3+ to form ferric oxalate which was a better substrate than Fe(Ⅲ)ETDA. Activity of Fe 3+ reduction in intact roots and plasma membrane was compared when Fe(Ⅲ)EDTA,ferric citrate,or ferric oxalate was used as substrate. Not only the highest reducing activity but also the highest catalytic efficiency ( V max / K m) was observed with ferric oxalate as substrate for intact roots and plasma membrane reductase (Figs.2,3).The ferric reduction activity in intact roots and plasma membrane was increased in response to Fe defficiency (Table 1). It has been suggested that oxalate in soil may contribute to iron use efficiency in plants by chelating iron to render it readily reducible.更多还原