Proper supply of S increases GSH synthesis in the establishment and reduces tiller mortality during the regrowth of Tanzania guinea grass used for Cd phytoextraction
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Cadmium has caused serious environmental problems due to its phytotoxicity, requiring solutions to reduce its concentration in the environment. Because S can alleviate the phytotoxicity caused by heavy metals, the evaluation of the effects of S supply is a promising approach to address this problem. The aim of this study was to determine the influence of S in reducing the phytotoxicity caused by Cd to Panicum maximum Jacq. cv. Tanzania (guinea grass) and to evaluate the potential of this grass for Cd phytoextraction.
Materials and methods
Tanzania guinea grass was cultivated in a nutrient solution to evaluate the combinations of five rates of S (0.1, 1.0, 1.9, 2.8, and 3.7 mmol L−1) and five rates of Cd (0.0, 0.5, 1.0, 1.5, and 2.0 mmol L−1), in a 52 fractional factorial design with six replications. Six plants were grown per pot in two growth periods to evaluate the effect of Cd on the establishment (51 days of age) and on the regrowth (18 days of growth) of the plants. During regrowth, Cd was not supplied in the nutrient solution. At the end of each growth period, growth parameters, concentrations of S and Cd, Cd transport factor, and concentrations of hydrogen peroxide (H2O2), malondialdehyde, reduced glutathione, and oxidized glutathione were evaluated.
Results and discussion
On the establishment of Tanzania guinea grass, application of Cd reduced mass production by 39 % due to the increases in the concentration of Cd (30 times compared with the treatment without Cd) and in lipid peroxidation (124 %). During regrowth, the residual effect of Cd resulted in a lower number of tillers (62 %) and leaves (89 %) caused by the increase in concentrations of Cd, H2O2 (49 %), and lipid peroxidation, which resulted in a 65 % lower dry mass production. The proper supply of S reduced concentration of Cd and tiller mortality rate due to the residual effect of Cd on the regrowth of the grass. Mass production by the roots was 43 % lower because of Cd, but the transport of Cd from roots to shoots increased. The increase in the concentration of glutathione (GSH) associated with a possible higher activity of antioxidant enzymes alleviated the phytotoxic effects of Cd on the guinea grass.
The supply of S reduces the phytotoxicity caused by Cd to guinea grass, especially during the regrowth of the plant, when the concentration of Cd is higher because of the transport from roots to shoots. Tanzania guinea grass showed to be very promising for phytoextraction of Cd due to its high mass production, even when Cd was largely available in the nutrient solution.
KeywordsEnvironmental pollution Glutathione Heavy metals Pastures Tolerance mechanisms
The authors would like to thank the São Paulo Research Foundation (FAPESP) for the Master’s fellowship granted to the first author (#2012/12894-3) and for the financial aid (#2012/11859-0) provided for the development of the study, the Scientific and Technological Brazilian Council (CNPq #306403/2013-7), Dr. Roberta Corrêa Nogueirol for her collaboration in the development of the research project, and Dr. Lucélia Borgo for her assistance in the analyses involving the antioxidant system.
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