Modulation of Redox Balance in Shepherd’s Purse by the Apple Dihydrochalcone Phloretin

Phloretin is a naturally occurring dihydrochalcone, predominantly found in apple species (Malus spp.), that has recently attracted attention as a phytotoxic allelochemical with potential for bioherbicide development. However, the contribution of oxidative stress to its phytotoxic effects remains unclear and appears to be species-dependent. We investigated the involvement of oxidative stress in phloretin-induced phytotoxicity in Capsella bursa-pastoris (L.) Medik. by assessing oxidative stress markers alongside enzymatic and non-enzymatic antioxidant responses. A two-week exposure to 500 μM phloretin significantly increased total phenolic content and ABTS radical scavenging capacity. Total superoxide dismutase (SOD) activity increased, accompanied by enhanced Mn-SOD band intensity, indicating an intensified mitochondrial antioxidant response. In contrast, catalase (CAT) activity decreased, whereas peroxidase (POX) activity remained unchanged. The increased SOD activity, without a corresponding increase in H2O2-scavenging enzymes, was accompanied by elevated malondialdehyde (MDA) and proline levels, suggesting that the antioxidant response was insufficient to restore cellular redox homeostasis and prevent oxidative damage. Overall, our findings demonstrate that phloretin treatment leads to a redox imbalance accompanied by increased lipid peroxidation despite activation of antioxidant defenses, identifying oxidative stress as an important, species-dependent component of its phytotoxicity.