Detoxification of aluminum by Ca and Si is associated to modified root cell wall properties

Aluminum (Al) is an obstacle to crop production in acidic soils globally. Cations such as Ca and Si are capable of detoxifying toxic metals, especially Al. However, the underlying mechanism of the ameliorative effect is still unclear. In this study, effects of Ca and Si alleviating Al toxicity were investigated on soybean ( Glycine max ) through root elongation, cation exchange capacity (CEC), Al concentration of apical root tissues, cell wall fractions and Fourier Transform infrared spectroscopy (FTIR) spectra features. The root expressed a higher elongation rate in the presence of Ca or Si under 32 µM Al. Ruptures were observed on the root surface under low concentrations of Ca and Si, while high concentrations of Ca and Si offset Al symptoms. Additional Ca or Si treatments increased CEC of the root and decreased Al accumulation of apical root tissues. For the four fractions of the cell wall, Ca and Si increased pectin, hemicellulose, and cellulose concentrations to a different degree. Characteristic absorption FTIR peaks were located at 1710, 1453, 1247, and 1154 cm −1 , indicating the presence of esterified pectin, carboxyl, and cellulose. Compared with control, the position of peaks under Ca or Si was moved to a higher wavenumber direction and stronger peaks intensity was observed. Detoxification of Al toxicity by Ca and Si is due to modified root cell wall fraction composition and their functional groups, which could inhibit transmembrane transport of Al into protoplast.