DNA Damage and Repair Mechanisms in Duckweed ( Spirodela polyrhiza ) Under Ultraviolet-B (UV-B) Light Stress

Exposure to Ultraviolet-B (UV-B) light can adversely affect plant growth and cellular integrity by inducing oxidative stress and DNA damage. In this study, we investigated UV-B-induced DNA damage and repair responses in the aquatic monocotyledonous plant species Spirodela polyrhiza (duckweed). We exposed 13-day-old duckweed plantlets to broadband UV-B light for 1-10 min, followed by recovery periods of up to 24 h under normal growth conditions. We observed progressive chlorosis, wilting, and diminished plant vigor with longer duration of UV-B light exposure. Agarose gel electrophoresis demonstrated compromised genomic DNA integrity immediately after UV-B light treatment, with partial restoration of DNA quality during recovery. Immuno-slot blot assays established the accumulation of two major UV light–induced photoproducts, cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidone photoproducts [(6-4)PPs] in a dose-dependent manner following UV-B light exposure. Notably, the abundance of these DNA lesions declined substantially after recovery, indicating activation of endogenous DNA repair mechanisms. Staining with 3,3′-diaminobenzidine revealed elevated accumulation of hydrogen peroxide immediately following UV-B exposure, suggesting enhanced oxidative stress. Collectively, these findings demonstrate that S. polyrhiza possesses efficient mechanisms for sensing, repairing, and mitigating DNA damage induced by the oxidative stress resulting from UV-B light exposure. This study highlights the potential of duckweed as an effective model system for investigating DNA damage and repair pathways under UV-B light stress in plants.