Aqueous Extract of Limnospira platensis Provides Protection Against Microcystin-Induced Oxidative Stress in Hydroponic Culture of Radish (Raphanus sativus)

Abstract

The eutrophication of aquatic ecosystems often triggers the excessive growth of cyanobacteria, many of which release toxic metabolites such as microcystins (MCs). When irrigation water is contaminated by these compounds, adverse consequences may arise for plants as well as for animal and human health. In contrast, certain non-toxic cyanobacterial species like Limnospira platensis are increasingly regarded as valuable tools for sustainable agriculture, given their ability to enhance plant nutrition, growth, yield, and stress tolerance while also mitigating the detrimental impacts of MCs. The present work aimed to investigate the potential of L. platensis extract to enhance growth, physiological responses, and tolerance of radish (Raphanus sativus) plants stressed with Microcystis aeruginosa extract containing microcystins. Experiments were conducted in a hydroponic system under controlled environmental conditions, where radish seedlings were cultivated in perlite and exposed for 45 days to M. aeruginosa extract (10 and 40 µg/L of MCs) and L. platensis extract (0.1 and 1 g/L), applied either separately or in combination. The results showed that the application of L. platensis extract, especially at 1 g/L in combination with 40 µg/L of MCs, decreased the bioaccumulation of MCs from 8.81 to 5.35 µg/kg FW in the leaves and from 14.64 to 10.15 µg/kg FW in the taproots. In addition, it significantly stimulated radish growth and improved several biochemical parameters. In contrast, exposure to MCs at 10 and 40 µg/L negatively affected growth, chlorophyll pigments and protein contents while promoting the accumulation of malondialdehyde (MDA), polyphenols and sugars. The activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were also increased under MCs stress, suggesting activation of the antioxidant defense system in response to oxidative damage. Combinations of MCs with L. platensis extract, especially at 1 g/L, improved antioxidant enzyme activities by significantly reducing MDA levels, biometric parameters, chlorophyll pigment, and protein and sugar contents. These results indicate that the application of L. platensis extract as a biostimulant can improve radish development, growth, and tolerance to MC-induced stress.