Oxidative stress induced in rice suspension cells exposed to microcystin-LR at environmentally relevant...

Microcystins (MCs) are cyclic heptapeptide hepatotoxins that are highly soluble in water and can be transferred to farmland through irrigation with potentially substantial effects on crops, especially rice. In order to investigate the possible negative effects of microcystin-LR (MC-LR) on rice, the oxidative stress induced in rice suspension cells exposed to MC-LR at environmentally relevant concentrations (0.05, 0.5, 5.0, and 50.0 μg·L^-1) was investigated. Results showed that the exposure to MC-LR at 0.5-50.0 μg·L^-1 resulted in a significant decline in viability of rice suspension cells and an increase in malondialdehyde (MDA) contents. In the 50.0-μg·L^-1 MC-LR treatment group, the content of MDA was as much as 5.39 times that of the control group after 6 days of exposure. The excess MDA production indicated that MC-LR exposure has caused lipid peroxidation damage in rice cells, whereas these negative effects could be recovered over time when suspension cells were exposed to low concentration of MC-LR (0.05 μg·L^-1). When exposed to MC-LR for 3 days, the O₂^- content in all treatment groups increased significantly compared with the control group. Additionally, the antioxidant system of rice suspension cells initiated a positive stress response to MC-LR exposure. Indeed, peroxidase (POD) played an active role in the removal of reactive oxygen species (ROS) in rice suspension cells during the early period of exposure, while total superoxide dismutase (T-SOD) was induced after 6 days. Similarly, after 6 days of exposure, the anti-superoxide anion free radical activity (ASAFR), glutathione (GSH), and glutathione-S transferase (GST) in rice suspension cells were higher than that in the control group. These results provided a comprehensive understanding of the exposure time- and dose-dependent oxidative stress induced by the environmentally relevant concentrations of MC-LR in rice suspension cells.