Effects of exogenous manganese on its plant growth, subcellular distribution, chemical forms, physiological and biochemical traits in Cleome viscosa L.

Cleome viscosa L. is a promising species for the phytoremediation of Mn-contaminanted soil. To reveal the adaptive mechanisms of species to Mn stress, plant growth, Mn subcellular distribution, Mn chemical forms, and plant physiological and biochemical traits were characterized in plants grown under different concentrations of Mn2+ (0, 1000, 5000, 10000, 15000 and 20000 μM). The results showed that C. viscosa plant biomass initially increased and then decreased with rising Mn treatment concentration. C. viscosa plants can accumulate high levels of Mn in roots and leaves, and both the bioconcentration factor (BCF) and the translocation factor (TF) exhibited values higher than one. Mn was primarily retained in the cell wall and soluble fractions. Predominant chemical forms of Mn were pectate and protein, phosphates, and oxalates-integrated Mn. The activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and the contents of proline, soluble sugar, and soluble protein initially increased and then decreased with enhancing Mn treatment concentration, whereas the malondialdehyde (MDA) content simultaneously displayed a gradual increase. Combined, these results indicate that C. viscosa can tolerate Mn-stress conditions by increasing antioxidant enzyme activities and non-enzymatic metabolites contents. In addition, Mn immobilization in the cell wall and soluble fractions, alongside the storage of Mn in low-activity chemical forms are further important mechanisms to cope with high environmental Mn concentration. This study reveals the adaptive mechanisms of plants to Mn stress, and provides a theoretical basis for the use of C. viscosa as a candidate phytoremediation plant for Mn-contaminated soil.