Effects of antimony stress on growth, structure, enzyme activity and metabolism of Nipponbare rice (Oryza sativa L.) roots.

Some antimony (Sb) contaminated areas are used for rice cultivation in response to economic demands. However, little is known about the effects of Sb stress on the growth and metabolism of rice roots. Thus, a hydroponic experiment was carried out on the growth, root anatomy, enzyme activity, and metabolism of Nipponbare rice (Oryza sativa L. ssp. japonica cv. Nipponbare) under varying levels of Sb (III) stress (0 mg L, 10 mg L, and 50 mg L). With the increase of Sb concentration, rice root length and root fresh weight declined by 67.8 % and 90.5 % for 10 mg L Sb stress and 94.1 % and 98.4 % for 50 mg L Sb stress, respectively. Anatomical analysis of cross-sections of Sb-treated roots showed an increase in cell wall thickness and an increase in the number of cell mitochondria. The 10 mg L and 50 mg L Sb stress increased the activity of enzyme superoxide dismutase (SOD) in root cells by 1.94 and 2.40 times, respectively. Compared to the control, 10 mg L Sb treatment increased the activity of catalase (CAT) and peroxidase (POD), as well as the concentrations of antioxidant glutathione (GSH) in the root by 1.46, 1.38, and 0.52 times, respectively. However, 50 mg L Sb treatment significantly decreased the activity or content of CAT, POD and GSH by 28.1 %, 13.5 % and 28.2 %, respectively. Nontargeted LC/MS-based metabolomics analysis identified 23 and 13 significantly differential metabolites in rice roots exposed to 10 mg L and 50 mg L Sb, respectively, compared to the control. These differential metabolites were involved in four main metabolic pathways including the tricarboxylic acid cycle (TCA cycle), butanoate metabolism, alanine, aspartate and glutamate metabolism, and alpha-linolenic acid metabolism. Taken together, these findings indicate that Sb stress destroys the structure of rice roots, changes the activity of enzymes, and affects the metabolic pathway, thereby reducing the growth of rice roots and leading to toxicity.