Impact of synthetic and herbal dyes on photosynthesis and ROS scavenging enzyme activities in Spirodela polyrhiza

Synthetic colors (SCs) are widely used in various industries, yet their discharge into aquatic ecosystems poses a significant environmental threat. This study investigates the impact of SCs and herbal colors (HCs), used during the 'festival of colors- Holi in India' on the physiological and photosynthetic performance of Spirodela polyrhiza, an aquatic macrophyte known for its bioindicator potential. The effects were assessed through chlorophyll a fluorescence transient analysis (O-J-I-P), biochemical assays, and energy flux parameters. The results indicate that exposure to SCs severely disrupted PSII functionality, as evidenced by a drastic decline in the quantum yield of primary photochemistry (φPo), electron transport efficiency (φEo), and performance index (PIcs). At 2.5 g/L SC, a 94.18% reduction in trapped energy flux (TR₀/CSm) and a 96.1% decline in electron transport rate (ET₀/CSm) were observed, along with a significant decrease in chlorophyll content. Furthermore, SCs markedly reduced the plastoquinone pool size, leading to impaired photosynthetic electron transport. Antioxidant enzyme activities, including superoxide dismutase (SOD) and catalase (CAT), were significantly elevated in SC-treated fronds, indicating oxidative stress. Conversely, no major alterations were observed in plants grown on HCs, which maintained stable photosynthetic parameters and even exhibited enhanced PIcs and φEo, likely due to nutrient enrichment from organic flower-derived pigments. The findings establish S. polyrhiza as an effective bioindicator for monitoring SC pollution in aquatic environments. This study underscores the urgent need to replace synthetic dyes with eco-friendly alternatives, as HCs not only mitigate environmental risks but also enhance growth and productivity of aquatic plants. The research provides novel insights into the differential physiological responses of aquatic plants to SCs and HCs, emphasizing the importance of promoting sustainable, non-toxic coloring agents to safeguard aquatic ecosystems.