Abstract: 【Objective】 To examine whether low- molecular weight organic acids (LMWOAs) in root exudates of amaranth play a role in Cd hyperaccumulation, we compared the amounts and composition of LMWOAs collected from two cultivars of amaranth，Zibeixian ，a low Cd accumulator，and Tianxingmi，a high Cd accumulator. 【Method】 Plants were grown hydroponically and three treatment (Cd 0、1 and 2.5 mg/L ) were later imposed for 1 wk before collection of LMWOAs. 【Result】 With the increase of solution Cd concentration, the biomass and its components of Zibeixian decreased dramatically, while those of Tianxingmi remained stable. In all treatment, total amount of LMWOAs in rhizosphere of Tianxingmi were significantly higher than that in Zibeixian，and the content of LMWOAs in two cultivars followed the same tendency, i.e. citric>malic>acetic>propinonic>butyric, and citric acid and malic acid predominated the composition of LMWOAs. The percent distribution of total LMWOAs of Zibeixian was very similar to Tianxingmi. With the increase of solution Cd supply, the content of LMWOAs in rhizosphere increased dramatically for both two cultivars, and the increment of LMWOAs of Tianxingmi was found to be greatly higher than that of Zibeixian. 【Conclusion】Therefore, Cd accumulation in amaranth was highly related to the total amount of LMWOAs in rhizosphere，and the differential increment of LMWOAs in the rhizosphere induced by Cd exposure may played an important role for Cd bioaccumulation by the high and low Cd accumulating cultivars of amaranth.

Key words: amaranth, cadmium, low- molecular weight organic acids (LMWOAs)