Unraveling the responses of methylparaben on bioconcentration, stomatal regulation, photosystem II dynamics and scavenging activity in Lemna trisulca.

Methylparaben (MP) is a pseudo-persistent emerging contaminant ubiquitously detected in aquatic environments, where its endocrine-disrupting activity threatens both ecosystem function and human health, driving interest in sustainable phytoremediation approaches using submerged macrophytes such as Lemna trisulca. This study presents a comprehensive assessment of physiological, biochemical, and remediation responses of L. trisulca exposed to MP at Control, 10, 50, 100, 250, 500, and 1000 mg L-1 for 14 days. Tissue MP accumulation, quantified by HPLC, showed a dose-dependent increase from 6.98 to 496.92 mg kg-1 fresh weight, while the bioconcentration factor decreased from 9.97 to 0.58 and removal efficiency declined from 93.6% to 14.9%, indicating efficient paraben removal at concentrations up to 50 mg L-1, where high bioconcentration coincided with preserved physiological integrity. Relative growth rate remained unchanged at low doses but markedly decreased at 500 and 1000 mg L-1, where photosynthesis was severely impaired and PSII reaction-centre inactivation was evident. Oxidative stress, reflected by H2O2 and lipid peroxidation markers, emerged progressively above 100 mg L-1, defining a clear stress threshold. Antioxidant enzyme responses were dose-dependent and stressor-specific: catalase and peroxidase provided substrate-independent H2O2 detoxification across all doses, whereas GPX and GST activities, although elevated, were rendered functionally inefficient by progressive glutathione depletion at higher concentrations. At low MP doses, autonomous ascorbate recycling within the ascorbate-glutathione cycle compensated for glutathione arm collapse and sustained cellular protection, whereas above 100 mg L-1 this compensatory capacity was lost, resulting in uncontrolled oxidative damage. These findings establish L. trisulca as a promising nature-based solution for paraben-contaminated waters and demonstrate that the functional integrity of the ascorbate-recycling arm of the ascorbate-glutathione cycle, sustained by adequate substrate availability, is a key biochemical determinant of phytoremediation performance under organic contaminant stress.