Investigation of subcellular distribution, physiological, and biochemical changes in Spirodela polyrhiza as a function of cadmium exposure

Cadmium (Cd) is considered to be the most phytotoxic heavy metal pollutant. Duckweeds are often used in ecotoxicological investigations as experimental model systems due to their ability to accumulate toxic metals. In this study, accumulation, subcellular distribution, and alterations of metabolic fingerprinting and physiology were evaluated in Spirodela polyrhiza exposed to 2.5, 5, and 10 pi Cd for 4 d. The accumulation of Cd increased in a concentration dependent manner. Subcellular fractionation of Cd-containing tissues indicated that 52%-61% of the metal was localized in cell walls and 37%-46% in the soluble fraction, and lowest concentrations were found in cellular organelles. Fourier transform infrared spectrometry analysis indicated that carbonyl, hydroxyl, thiol, and amide groups might be involved in Cd uptake. Cd induced alterations in nutrient elements; for example, it significantly increased iron and calcium and reduced phosphorus and magnesium concentrations in S. polyrhiza. Cd-caused oxidative damage was evidenced by increased lipid peroxidation and decreased chlorophyll, protein, and unsaturated fatty acid contents - this was associated.with reductions in superoxide dismutase, glutathione reductase, and catalase activities. However, S. polyrhiza could combat Cd-induced injury involving a mechanism of non-enzymatic antioxidants and proline and soluble sugar accumulation.