[Subcellular distribution and phytotoxicity of cadmium in Alternanthera philoxeroides leaves].

A hydroponic experiment was conducted to study the subcellular distribution of Cd and mineral elements in Alternanthera philoxeroides leaves and the leaves anti-oxidative capacity and chlorophyll, soluble protein, and phytochelatins (PCs) contents under the stress of different concentration (0, 0.05, 0.1, 0.2, 0.4 mmol x L(-1)) Cd. With the increasing concentration of Cd in culture medium, the Cd content in all subcellular components of A. philoxeroides leaves increased significantly, and mainly distributed in cell wall, followed by in soluble fractions, and in chloroplast and mitochondria. When the Cd concentration in the medium exceeded 0.2 mmol x L(-1), the Cd was more allocated in soluble fractions than in cell wall. Cd stress resulted in an obvious imbalance of mineral elements uptake. With the increasing concentration of Cd, the Ca content in all subcellular components, especially in cell wall, increased significantly, whereas the P and K contents in cell wall and soluble fractions as well as the Mg and Fe contents in chloroplast decreased. In the meantime, the soluble protein and chlorophyll contents showed a decreasing trend, the glutathione and ascorbic acid contents decreased after an initial increase, the total anti-oxidative capacity (T-AOC) increased progressively, and the PCs accumulated in large quantity. These results suggested that A. philoxeroides had definite resistance to the water body Cd, and there was a dosage-effect relationship between the Cd enrichment in the subcellular components of A. philoxeroides leaves and the phytotoxicity of Cd. The imbalance of the mineral elements in subcellular components and the decrease of soluble protein and chlorophyll contents in chloroplast indicated the obvious phytotoxicity of Cd, while the massive accumulation of Ca in cell wall and the increased levels of PCs and T-AOC suggested the stronger resistance of A. philoxeroides to Cd stress. There was a definite correlation between the PCs production by A. philoxeroides and the toxicity of Cd, suggesting that the PCs could be considered as a sensitive biomarker for estimating the Cd phytotoxicity.