Chlorophyll a fluorescence and metabolic profiling of Spirodela polyrhiza reveal the phytotoxic effects of pantoprazole as an emerging aquatic xenobiotic

Abstract

Pantoprazole (PPZ), a benzimidazole-class proton pump inhibitor widely used for treating gastric acid-related disorders, is increasingly detected in aquatic environments, yet its phytotoxic effects on freshwater macrophytes remain poorly understood. This study evaluated the effects of PPZ on Spirodela polyrhiza using physiological, biochemical, microscopic, and chlorophyll fluorescence approaches. Plants were exposed to varying PPZ concentrations for 8 days, and changes in growth, chlorophyll, carbohydrate and protein contents, malondialdehyde (MDA) levels, stomatal behaviour, and OJIP fluorescence transients were analysed. PPZ exposure significantly reduced relative growth rate, chlorophyll content, carbohydrate and protein accumulation, and photosynthetic electron transport, while markedly increasing MDA levels, indicating enhanced oxidative stress and membrane lipid peroxidation. Microscopic observations revealed pronounced stomatal closure in treated fronds, potentially associated with elevated intercellular CO₂ accumulation resulting from inhibition of the photosynthetic electron transport chain. OJIP fluorescence analysis demonstrated severe impairment of PSII photochemistry, including reductions in Fm, ΦPo, ΦEo, RC/CSm, and PI(csm). In contrast, non-photochemical energy dissipation parameters increased progressively, indicating enhanced excitation pressure and impaired electron transport. Overall, PPZ severely disrupted photosynthetic efficiency, PSII functionality, and metabolic homeostasis, highlighting its ecological risk in aquatic ecosystems.