Pedosphere 17(3): 352--359, 2007
ISSN 1002-0160/CN 32-1315/P
©2007 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Chemical composition of root and stem saps in relation to cadmium resistance and accumulation in Brassica parachinensis |
WU Qi-Tang1 , XU Zhao-Li1, YE Hui1 and J. W. C. WONG2 |
1 College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642 (China). E-mail: qitangwu@pub.guangzhou.gd.cn;
2 Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR (China) |
| ABSTRACT |
| Sap mixtures of the xylem, phloem, and vacuoles from low and high Cd accumulator varieties of Brassica parachinensis L. H. Bailey were analyzed under Cd stress to understand the biochemical mechanisms of Cd accumulation in plants. Low Cd accumulator (‘Teqing-60' ) and high Cd accumulator (‘Chixin-2' ) plants were grown in Cd-treated soil in pots in a greenhouse. Percentage of cell wall-bound Cd was estimated. pH level and the concentrations of amino acids, organic acids, anions, and cations in both stem and root saps were determined for the calculation of Cd speciations using the computer program GEOCHEM. The results showed that ‘Teqing-60' had a significantly higher (P ≤ 0.05) percentage of Cd bound to cell walls in roots and a significantly higher (P ≤ 0.05) pH in the root sap. ‘Teqing-60' also contained a higher concentration of total amino acids in both roots and stems compared with the high Cd accumulator variety ‘Chixin-2'. However, between the two accumulators, for stems and for roots, there were no significant differences in non-amino organic acids. GEOCHEM calculations showed that Cd in the root sap of ‘Teqing-60' mainly combined with amino acids, especially alanine. Compared with ‘Chixin-2', in the root sap of ‘Teqing-60', much lower levels of Cd as free ions or bound to simple ligands were found, indicating that less ‘Teqing-60' is transferred to stems and leaves. Cadmium activity in the shoot sap of ‘Teqing-60' was much lower than that in ‘Chixin-2'; therefore, ‘Teqing-60' exhibited higher Cd resistance. However, direct determination of the Cd complexes from xylem and phloem sap is needed to verify these results. |
| Key Words: Brassica parachinensis, cadmium, plant sap, resistance, speciation |
| Citation: Wu, Q. T., Xu, Z. L., Ye, H. and Wong, W. C. 2007. Chemical composition of root and stem saps in relation to cadmium resistance and accumulation in Brassica parachinensis. Pedosphere. 17(3): 352-359. |
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