Novel Insights into Microcystin-LR Uptake, Accumulation, and Toxicity Mechanisms in Lettuce (Lactuca sativa L.) Using a Protoplast Model

Prevalent microcystin-LR (MC-LR), a cyanotoxin, in agricultural fields compromises produce safety and threatens human health. However, little is known about its uptake and accumulation in plant cells and its resultant toxicity mechanisms. This study revealed that the MC-LR uptake into protoplasts was controlled by an active transmembrane transport process mediated by the protein carrier. MC-LR in the plant cells can enlarge the specific mitochondrial permeability transition pores and probably bind with the electron transport chain complex I (especially, NADH oxidoreductase 1, -30.59 kcal/mol of binding energy) and complex III (especially, cytochrome b, -36.98 kcal/mol of binding energy) via hydrophobic force and hydrogen bond. The interactions between MC-LR and the mitochondrial complex proteins block the electron transfer, causing high levels of reactive oxygen species (ROS), especially for H₂O₂. The MC-LR-induced ROS destroys the mitochondrial inner membrane structure and decreases the cell viability by 13.6-30.6% in a significant dose-dependent manner at 1-5 mg/L MC-LR stress. The findings provided direct evidence of MC-LR entry into the cells via active plasma membrane transport for the first time and clarified the associations between MC accumulation and its toxicity at cellular and molecular levels, thereby providing crucial insights for ensuring food safety and safeguarding human health.