Toxicity of Tris(2-chloroethyl) Phosphate (TCEP) to Alfalfa’s Root System: An Insight into TCEP’s Damage to Morphology, Respiration, and Antioxidant Systems

Tris(2-chloroethyl) phosphate (TCEP), as an organophosphate contaminant, poses a significant threat to the growth and development of plants, especially roots. This study aimed to clarify the mechanisms of TCEP’s toxicity and damage to root systems, as well as the mechanisms of its damage to the respiration and energy metabolism of alfalfa root cells. The results showed that TCEP obviously affected the root length, root surface area, root volume, and root diameter of alfalfa. With increasing stress intensity, the total mitochondrial respiration rate and Cytochrome C Oxidase (COX) pathway respiration rate progressively declined, while the Alternative Oxidase (AOX) pathway respiration rate and its proportion of total respiration gradually rose. In addition, adenosine triphosphate (ATP) content and root vigor were significantly reduced. Moreover, with an increase in TCEP concentration, root superoxide anion radical content in alfalfa root cells was significantly elevated, while superoxide dismutase (SOD) and catalase (CAT) activities were significantly lowered, and ascorbate peroxidase (APX) and peroxidase (POD) activities were significantly enhanced. The present study indicated that respiration was disrupted, causing a lack of ATP in root cells under TCEP. Both the overproduction of reactive oxygen species (ROS) from the mitochondrial respiratory electron transport chain (mECT) and the deficiency of ROS-scavenging enzymes caused ROS accumulation, which led to the destruction of the cell membrane structure and exacerbated the disruption of the respiratory metabolism. The disruption of the conversion and reuse of energy by TCEP affected root growth and development.