Decolorization and transformation of Reactive Red M5B by in vitro grown Solanum virginianum: enzymatic, antioxidative, and biochemical responses

Ab stract Textile industries continuously produce azo dye wastewater which contaminates soil and water bodies. Phytoremediation using plants has emerged as an eco-friendly and cost effective approach for the treatment of dye contaminated wastewater. Microorganisms and higher plants are increasingly considered effective biological systems for the treatment and breakdown of azo dye containing wastewater because of their low operational cost and environmental compatibility. In the present investigation, in vitro germination of Solanum virginianum seeds reached 65.7% on half strength Murashige and Skoog medium. The number of shoots produced from each axillary bud explant was 18 when 0.75 mg/L 6-benzylaminopurine (BAP) was supplemented. In vitro grown S. virginianum showed the ability to decolorize Reactive Red M5B (RRM5B) under controlled conditions. Lower dye concentrations of 10, 30, and 50 mg/L showed high decolorization efficiencies of 85–95% within 6-15 d, whereas intermediate concentrations of 70 and 90 mg/L resulted in approximately 50% degradation. At a higher concentration of 150 mg/L, only 17.8% degradation was observed after 21 d when different numbers of in vitro grown shoots (2, 4, 6, 8, and 10) were incubated in shaking culture vessels containing 50 mL of the dye solution. The amount of dye removed from the dye solutions increased with the increase in the number of shoots. Antioxidative, enzymatic, and biochemical responses indicated physiological adaptation of plants exposed to dye stress. Phenolic, flavonoid, alkaloid contents and the antioxidant analysis of the S. virginianum varied depending on the solvents used indicating the significant role that the solvent plays in the cold extraction process. Dye exposure resulted in a concentration dependent increase in the activities of tyrosinase, laccase, lignin peroxidase, peroxidase, catalase, superoxide dismutase (SOD), azo-reductase, and NADH-DCIP reductase in the shoots. Among these, catalase, azo-reductase, and NADH-DCIP reductase showed markedly higher activities in treated plants compared with the respective controls. HPLC analysis suggested transformation of the dye molecule following plant exposure. Whole plants of S. viginianum can be further exploited to tolerate, accumulate and metabolize RRM5Bdye or environmental cleanup.