Different Response to Excess Iron and Zinc in Roots of Monocot and Dicot Plants Treated by Silicon

Abstract Aims Nutrient changes in the plant root environment modify root growth and development via alterations in cell wall-associated enzyme activities and components. Methods This research evaluated the effects of silicon (Si) supply (1.5 mM) on the root apical (AP) and basal parts (BP) of rice and wheat (as monocots), canola and cotton (as dicots) plants exposed to excess Fe (150 mg L-1) and Zn (150 µg L-1). Results The +Fe treatment resulted in increased enzymes activity of PAL, cell wall POD, and PPO in the root AP of rice and wheat. The +Fe and +Zn increased the content of phenolic compounds in both root AP and BP of these plants. Also, the activity of cell wall POD was increased in all plants treated with +Fe+Si and some +Zn+Si. In Si-treated (+Si) plants, the activity of PAL, cell wall POD, and PPO significantly increased in the root AP of rice and wheat, while Si did not significantly affect enzyme activities in canola and cotton. Additionally, in +Si treated plants, the content of phenolic compounds decreased in the root AP of rice and wheat. During the PCA analysis of the FTIR spectra, discernible modifications in the cell wall components were observed in monocot plants (especially rice) upon treatment with +Si and +Fe, However, treated dicot plants did not show significant differences. Conclusions This study investigated that Si caused more changes in the cell wall at the root AP of monocots than dicot plants, and these changes were exaggerated by +Fe+Si treatment.