[en] The effects of aluminum (Al) ion on plant biosystem were investigated using tandem accelerator mass spectrometry. Distribution of Al incorporated in cell organelle was investigated with water-cultured Brachiaria ruziziensis, a subtropical pasture aiming to elucidate the behaviors of Al element in Al-resistant plants. The intracellular amount of Al was determined using radioactive Al (²⁶Al) as a tracer. The concentration of Al was highest in the nucleus than other cell organelle. Then, intracellular distribution of Al was investigated in cell culture system of acid resistant and Al-resistant B. ruziziensis. The optimum temperature for the growth of B. ruziziensis under Al stress conditions at pH 3.5-4.0 was significantly lower than that of the ordinary culture conditions at pH 5.8. The results of electrophoresis suggested that Al incorporated in the acid conditions might exist as a complex bound to several different proteins in the cell. The localization of Al to the nucleus was more distinct in the Al-resistant cells than the sensitive ones. Then, relationship between Al sensitivity and viral sensitivity was investigated with the barley. Formation of necrotic streak was induced by BSMV virus under stress conditions of a low concentration of Al at pH 6. Such necrotic streak was more easily induced as an increase in the Al concentration Ultra-sensitive AMS method was able to detect 10⁷-10⁸ Al atoms. In Al-resistant plant, its accumulation in the nucleus or mitochondria was greater than that in a sensitive one. Therefore, it was suggested that Al-resistant mutants have larger capacities of the nucleus and mitochondria for Al accumulation than that of a sensitive strain. (M.N.)