Chen Rong Fu, Shen Ren Fang, Gu Pei, Dong Xiao Ying, DU Chang Wen, Ma Jian Feng
State Key Laboratory of Soil and Sustainable Agriculture (Institute of Soil Science, Chinese Academy of Sciences), Nanjing 210008, China.
Ann Bot. 2006 Aug;98(2):389-95. doi: 10.1093/aob/mcl110. Epub 2006 May 30.
Rice (Oryza sativa) is an aquatic plant with a characteristic of forming iron plaque on its root surfaces. It is considered to be the most Al-tolerant species among the cereal crops. The objective of this study was to determine the effects of root surface iron plaque on Al translocation, accumulation and the change of physiological responses under Al stress in rice in the presence of iron plaque.
The japonica variety rice, Koshihikari, was used in this study and was grown hydroponically in a growth chamber. Iron plaque was induced by exposing the rice roots to 30 mg L(-1) ferrous iron either as Fe(II)-EDTA in nutrient solution (6 d, Method I) or as FeSO(4) in water solution (12 h, Method II). Organic acid in root exudates was retained in the anion-exchange resin and eluted with 2 m HCl, then analysed by high-performance liquid chromatography (HPLC) after proper pre-treatment. Fe and Al in iron plaque were extracted with DCB (dithionite-citrate-bicarbonate) solution.
Both methods (I and II) could induce the formation of iron plaque on rice root surfaces. The amounts of DCB-extractable Fe and Al on root surfaces were much higher in the presence of iron plaque than in the absence of iron plaque. Al contents in root tips were significantly decreased with iron plaque; translocation of Al from roots to shoots was significantly reduced with iron plaque. Al-induced secretion of citrate was observed and iron plaque could greatly depress this citrate secretion. These results suggested that iron plaque on rice root surfaces can be a sink to sequester Al onto the root surfaces and Fe ions can pre-saturate Al-binding sites in root tips, which protects the rice root tips from suffering Al stress to a certain extent.
水稻（Oryza sativa）是一种水生植物，其根系表面具有形成铁膜的特性。它被认为是谷类作物中最耐铝的物种。本研究的目的是确定在有铁膜存在的情况下，水稻根系表面铁膜对铝的转运、积累以及铝胁迫下生理反应变化的影响。
本研究使用粳稻品种越光，在生长室中进行水培。通过将水稻根系暴露于营养液中30 mg L(-1) 的亚铁离子（以Fe(II)-EDTA形式，6天，方法I）或水溶液中的FeSO(4)（12小时，方法II）来诱导铁膜形成。根系分泌物中的有机酸保留在阴离子交换树脂中，并用2 m HCl洗脱，经过适当预处理后通过高效液相色谱（HPLC）进行分析。用连二亚硫酸盐-柠檬酸盐-碳酸氢盐（DCB）溶液提取铁膜中的铁和铝。
两种方法（I和II）都能诱导水稻根系表面形成铁膜。有铁膜存在时，根系表面DCB可提取的铁和铝含量比没有铁膜时高得多。根尖中的铝含量因铁膜而显著降低；铁膜显著减少了铝从根向地上部的转运。观察到铝诱导的柠檬酸分泌，铁膜可大大抑制这种柠檬酸分泌。这些结果表明，水稻根系表面的铁膜可以作为一个汇，将铝螯合到根系表面，并且铁离子可以预先饱和根尖中的铝结合位点，从而在一定程度上保护水稻根尖免受铝胁迫。
