Keywords: 
• multi-wall carbon nanotubes (MWCNTs) /
• phytoxicity /
• rice seedling /
• root damage /
• oxidative stress /
• cell membrane damage

Abstract: This study investigated the phytoxicity of multi-wall carbon nanotubes (MWCNTs) of various concentrations (10, 50, 100 mg·L^-1) on rice seedlings. Detailed toxic mechanisms were explored by measuring the growth index of seedlings, oxidative stress, cell membrane damage, and the variation of physiological functions in roots. It was observed that a significant loss was detected in fresh weights of shoots and roots at 100 mg·L^-1 of MWCNTs, which were decreased to 87.6%±1.1% and 69.2%±7.8% of the control, respectively. Based on the deep insights into root tests, the results demonstrated that the oxidative stress and cell membrane damage mainly took place at higher concentrations of MWCNTs (i.e.,100 mg·L^-1). Compared with the control sample, the catalase (CAT) activity was increased from (8.8±1.6) to (16.3±2.8) U·mg^-1 prot (protein). Simultaneously, the same increasing trend was found for malondialdehyde (MDA) content, which changed from (8.0±0.3) (the control) to (15.1±1.4) µmol·g^-1 FW (fresh weight). Nevertheless, the physiological enzyme activities decreased to a greater level even after exposure to the lowest MWCNTs concentration (10 mg·L^-1). Transmission electron microscope (TEM) analysis was carried out for the observation of the root cells. It was found that the MWCNTs were distributed in the root cells, which further verified the uptake of MWCNT by the root cells.