Chromium "(VI)" phytoremediation using Azolla pinnata: effects on Vicia faba growth, physiology, cytogenetics, and gene expression profiling

Abstract

Background

One of the primary challenges that the expanding population faces is water scarcity. Thus, a global imperative has been established to safeguard extant water resources and optimize their utility through sustainable practices and efficient management. In the present investigation, Azolla pinnata, a pteridophyte (fern), was employed to phytoremediate Cr (VI) from chromium-polluted water. The potential of this treated water for agricultural purposes was verified through the use of Vicia faba plants.

Results

In vitro, A. pinnata effectively remediates Cr (VI) from an array of liquid concentrations (0.05 to 90 ppm) in a ratio of 25:1 {volume (mL): fresh weight of Azolla (g)} after 2 days incubation period at room temperature. At low concentrations (0.1 ppm), the phytoremediation capacity peaked at 70%, falling to 19.53% at a high concentration (90 ppm). Upon continuous irrigation with Cr-polluted water (0.05 to 50 ppm), the in vivo pot experiment on Vicia faba plants revealed high Cr accumulation in the roots reached 52.5 mg Kg ^-1 dry weight (Dwt) at the 50 ppm Cr treatment. Nevertheless, a reduced Cr content of 19.5 mg Kg ^-1 Dwt was observed when the plants were irrigated with 50 ppm Cr-polluted water that had been treated with Azolla. At 50 ppm of Cr, Azolla's treatment significantly increased shoot length, fresh weight, and Chl a content to 25.25 cm, 3.4 g, and 6.5 mg g ^-1 Dwt, respectively, up from 10.25, 1.8, and 4.7 in untreated plants. The chromosomal aberrations were significantly induced in the dividing cells of all Cr treatments, with the highest value of 4.8% at 50 ppm. This value was reduced to 2.88% at the same concentration when treated with Azolla. At a concentration of 10 ppm Cr, the mitotic index was significantly improved to 6.99% when combined with Azolla, as opposed to 3.63% when the same concentration was used without Azolla. The DNA degradation assay showed partial DNA degradation at 50 ppm Cr, which the Azolla treatment eliminated. Furthermore, the gene expression levels of both the PM H ⁺-ATPase and the calcium-dependent protein kinase CDPK5 were upregulated in response to Cr, despite the fact that the expression level was altered in a dose- and concentration-dependent manner by Azolla treatment.

Conclusion

Azolla exhibits substantial potential for reducing the detrimental effects of chromium stress including oxidative stress on plants. It modulates stress-related gene expression, protects DNA integrity, enhances cell mitosis, and reduces chromosomal damage. These results indicate that Azolla has the potential to be a valuable asset in phytoremediation strategies for chromium-contaminated environments, and that it may enhance plant survival and growth under Cr stress conditions.

Key message

Azolla pinnata can be effectively utilized as an environmentally-friendly method to remediate chromium-contaminated water for agricultural usage.

Highlights

• A. pinnata remediates Cr(VI) from liquid concentrations with 70% phytoremediation capacity at low concentrations.

•  A. pinnata treatment greatly decreased Cr buildup and improved Vicia faba growth under Cr stress.

• In Vicia faba, A. pinnata increased mitotic index, reduced Cr-induced chromosomal aberrations, and modulated the expression of genes linked to stress.