Contrasting Cd accumulation in rice grain

摘要

The presence of Cd~(2+) in rice is a risk to human health. The identification of rice genotypes able to exclude Cd~(2+) from grain could be a low-input solution for reducing the possibility of introducing the toxic metal into the food chain. Results showed that there was a large variability between the most important European rice cultivars hi accumulating Cd~(2+) in the grain when grown on a polluted soil (3.1 mg kg~(-1) total Cd; 1.6 mg kg~(-1) EDTA-extractable). The shorter the duration of the sowing-ripening period of the cultivar; the higher the Cd concentration in grain. This correlation seemed to be not due to unspecific sink strength of the cultivar, since it was not confirmed for Zn~(2+) and Mn~(2+). Comparison between grain/bundle leaf ratios for Cd~(2+), Zn~(2+) and Mn~(2+) suggested that the flux of Cd~(2+) toward grain was mainly supported by xylem. The root capacity in retaining Cd~(2+) increased with the concentration of the metal in the growing medium (from 50% up to 80% for Cd~(2+)ranging from 0.01 mu M to 1 mu M). The amount of Cd retained in the root correlated to a massive phytochelatin (PC) synthesis at only 1 mu M Cd concentration in the medium. A condition which is very far from actual Cd~(2+) content of rice-field polluted soils.