Assessment of the phytoremediation potential of Zinnia elegans L. plant species for hexavalent chromium through pot experiment

Pot experiments were conducted in a completely randomisedstrip-plot design to investigate the root morphological variations, flowering stages (no. of buds, no. of buds blooming and no. of mature flowers) toxicological, physiological and biochemical changes in an ornamental plant Zinnia elegans (L.) using graded concentrations of hexavalent chromium (K₂Cr₂O₇). The study also assessed the chromium bioaccumulation and translocation potential of Zinnia elegans from the contaminated soil. The physio-morphological parameters such as Chlorophyll a fluorescence transient (O–J–I–P), quantum yield of photosystem II (φP₀), photosynthetic performance index of primary photochemistry (PIφ), length of roots and shoots, biomass, total chlorophyll, carotenoid, protein, proline, reducing sugar content and activity of antioxidant enzymes viz guaiacol peroxidase (POX), ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT) were analysed after 30, 45 and 60d of treatment. The experiment showed a relationship between an increase in the accumulation of chromium in root and shoot of plants and an increase in the concentrations of hexavalent chromium. However, the length, biomass, φP₀, PIφ, area under OJIP curve, chlorophyll and protein contents of the plants were decreased at higher concentration of Cr+6 (75ppm). disturbance indices M0 and VJ derived from Chl. a fluorescence exhibited higher values indicating Cr+6 induced stress at higher concentrations (>50ppm). However, the activity of antioxidant enzymes and proline contents were increased with the application of higher concentration of chromium, which indicates that the plants adaptive defense system relating to elevated Cr+6 induced oxidative stress. The number of root hairs initially decreased with increase in the concentration of Cr+6 but at higher concentration of Cr+6 (75ppm) the number of root hairs were increased. The number of flowers and overall photosynthetic performance increased with the increase in Cr+6 concentration up to 25ppm. At the highest concentration of Cr+6 (75ppm), treated plants exhibited the least number of mature flowers. The experiments suggest that the Cr+6 stress leads leads to early flowering in Zinnia elegans L. species. This study demonstrates that phytoremedation of Cr+6 contaminated soils in mining sectors can be effectively carried out using non edible ornamental plants, thereby arresting the effects of the ion in the food chain.