p-Methoxycinnamic acid disturbs cellular respiration and increases the lignification of Euphorbia heterophylla roots

Herbicide-resistant plants evolved rapidly due to the recurrent use of active principles with only a few mechanisms of action. Today, discovering new herbicides is a pressing challenge. Here, the effects of p-methoxycinnamic acid were evaluated on root growth, cellular respiration, and lignification of the wild poinsettia weed (Euphorbia heterophylla L.). In primary roots, p-methoxycinnamic acid decreased root length and the mitotic index, followed by the loss of cell viability. At the cellular level, p-methoxycinnamic acid stimulated KCN-insensitive and KCN- and SHAM-insensitive respiration. Furthermore, it decreased KCN-sensitive respiration and ATP generation, a limiting factor for root growth. Disturbances in cellular respiration increased the H2O2 content and superoxide dismutase, catalase, and soluble peroxidase activity. p-Methoxycinnamic acid increased the activities of phenylalanine ammonia-lyase and cell wall-bound peroxidase. It also increased lignin, ferulic and p-coumaric acids, and cell wall-esterified p-methoxycinnamic acid. Collectively, these findings reveal the phytotoxic potential of p-methoxycinnamic acid on wild poinsettia. Field tests may point to new clues for using this compound as a potential herbicide.