Determination of heavy metal tolerance threshold in a bamboo species (Arundinaria pygmaea) as treated with silicon dioxide nanoparticles

Abstract

This research was carried out in a tissue culture study to analyze the impact of silicon dioxide nanoparticles on growth, photosynthesis and protective enzymes of a bamboo species (Arundinaria pygmaea) under three various heavy metal stresses (copper (Cu), manganese (Mn), and cadmium (Cd)). The treatments consisted of four concentrations of heavy metals (50, 100, 200, 400 μM) in combination with 100 μM silicon dioxide nanoparticles in comparison to controls. The results indicated that silicon dioxide nanoparticles under heavy metals (Cu and Mn) increased plant growth relative to the control, and they alleviated Cu and Mn toxicity, as reflected by significant increases in protective enzymes, chlorophyll content and fluorescence, as well as plant biomass and shoot length. However, the treatments under Cd concentrations resulted in a significantly decreased biomass and shoots length, which suggested that 100 μM silicon dioxide nanoparticles treatment was unable to prevent Cd accumulation in leaves through internal and external mechanisms. Overall, we concluded that 100 μM silicon dioxide nanoparticles increased the tolerance of bamboo species to heavy metals stress (Cu and Mn) and promoted plant growth indexes by evoking key mechanisms, including inhibiting metal accumulation in the leaves by the adsorption of the metal ions onto silicon dioxide nanoparticles, increasing levels of protective enzymes, and improving photosynthetic properties such as enhanced light-use efficiency and light transmission. We suggest that the combination of 100 μM silicon dioxide nanoparticles with concentrations of 100 and 200 μM heavy metals (Cu and Mn) can confer optimal growth rate, representing the threshold of the plant tolerance to heavy metals in a combination with 100 μM silicon dioxide nanoparticles.