AOBPreview originally published online on May 30, 2006
Annals of Botany 2006 98(2):389-395; doi:10.1093/aob/mcl110
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Response of Rice (Oryza sativa) with Root Surface Iron Plaque Under Aluminium Stress
1 State Key Laboratory of Soil and Sustainable Agriculture (Institute of Soil Science, Chinese Academy of Sciences), Nanjing 210008, China, 2 Graduate School of the Chinese Academy of Sciences, Beijing 100039, China and 3 Research Institute for Bioresources, Okayama University, 2-20-1, Chuo, Kurashiki, 710-0046 Japan
* For correspondence. E-mail rfshen{at}issas.ac.cn
Received: 19 February 2006 Returned for revision: 24 March 2006 Accepted: 10 April 2006 Published electronically: 30 May 2006
• Background and Aims 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.
• Methods 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 FeSO4 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.
• Key Results and Conclusions 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.
Key words: Rice (Oryza sativa), formation of iron plaque, root surface, Fe(II)-EDTA, aluminium (Al) stress, citrate secretion, DCB (dithionite–citrate–bicarbonate), root tip, Al translocation
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