Response of rice (Oryza sativa) with root surface iron plaque under aluminium stress.
OBJECTIVE
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 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.


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.
Chen
Rong Fu
RF
State Key Laboratory of Soil and Sustainable Agriculture (Institute of Soil Science, Chinese Academy of Sciences), Nanjing 210008, China.
Shen
Ren Fang
RF
Gu
Pei
P
Dong
Xiao Ying
XY
DU
Chang Wen
CW
Ma
Jian Feng
JF
D000327:Adsorption; D000535:Aluminum / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D019343:Citric Acid / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D012275:Oryza / Q000254:growth & development* / Q000378:metabolism / Q000502:physiology; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism
D019343:Citric Acid; D000535:Aluminum; D007501:Iron