Parameter determination involved in phytotoxicity and transport of cadmium in rice seedlings

Hydroponic experiments were conducted with rice seedlings to determine parameters involved in phytotoxicity and transport of Cadmium (Cd). Results showed that a linear decrease in relative growth rate and water use efficiency was observed in rice seedlings with increasing Cd concentrations. More severe inhibitory effects on both parameters were found at the 4-d treatment. The effective concentrations (EC) were estimated using the Levenberg-Marquardt Algorithm. The EC values obtained from the relative growth rate were always smaller than these from water use efficiency, indicating that the former was more sensitive to change of Cd than the latter. Phyto-transport of Cd was apparent, but the distribution of Cd in different parts of rice seedlings was different and roots were the dominant sink for Cd accumulation (p < 0.05). Although the translocation of Cd into shoots was detectable, more Cd was detected in shoots at the 4-d treatments than that at the 2-d treatments (p < 0.05). The partial correlation analysis suggested that the total accumulation rate of Cd was highly related to the doses of Cd supplied (p < 0.05). In conclusion, Cd is problematic at relatively low concentrations for rice seedlings, and inhibitory effects are highly dependent on the selected response endpoints and the duration of exposure periods.