Response of transporter proteins activities to Cd distribution in two wild rice roots

To investigate the characteristics of Cd transport and distribution in the wild rice roots, Oryza rufupogon Griff. and Oryza officinalis Wall. were used at research materials. Pot experiment was conducted to study the effects of different concentrations of Cd (0, 1, 5, 15 and 30 mg∙kg^-1) treatments on the root pectin content, root pectin methyl esterase(PME) activity, Cation/proton exchanger(CAX), heavy metal ATPase(HMA) and ATP-binding cassette protein(ABC) activities of wild rice. The difference in Cd flow rate of wild rice root was investigated through non-invasive micro-test technique (NMT). The results showed that the Cd in roots tended to increase with the increase of Cd treatment concentrations. Compared to the CK treatment (0 mg∙kg^-1 Cd), the root pectin content of O. rufupogon and O. officinalis under 30 mg∙kg^-1 Cd stress were significantly increased by 126.73 % and 109.69 %, respectively. The distribution of Cd contents in wild rice roots were all greater than those in shoots. Under Cd stress, the translocation factor of O. rufupogon (0.46-1.44) were all higher than those of O. officinalis (0.15-0.37). The Cd transport capacity in O. rufupogon was more stronger than in O. officinalis. The Cd content in the xylem sap of O. officinalis was lower than that of O. rufupogon. Compared to the CK, CAX and ABC activities in O. officinalis root under 30 mg∙kg^-1 Cd treatment were significantly increased by 11.03 % and 2.37 %, respectively. HMA activity in O. rufupogon root was significantly increased by 4.95 %. Cd flow rate in the root xylem of O. officinalis was higher than that of O. rufupogon. In root cells, the subcellular distribution of Cd contents showed cell wall > soluble components> organelles. With the Cd treatment concentrations increased, the percentage of Cd content in the soluble fractions of the root cells of wild rice showed an increasing. In general, the result showed that O. officinalis immobilized more Cd in the roots by influencing the pectin methyl esterification reaction through PME activity. Under high Cd stress, Cd was immobilized in root cell vacuoles of O. officinalis by enhancing roots CAX and ABC activities, whereas HMA activities were enhanced of O. rufupogon to reduce the damage caused by Cd.