Integrative analysis of maize and sunflower responses to copper stress reveals species-specific phytoremediation strategies.

BACKGROUND

Copper (Cu) contamination of arable land threatens crop yields, productivity, and environmental sustainability. While EDTA and IAA can enhance phytoremediation, understanding how different plant species exploit these amendments remains limited. This study tested the hypothesis that maize (Zea mays) and sunflower (Helianthus annuus) employ distinct physiological and Cu-accumulation strategies under Cu-induced stress.

METHODS

In a controlled pot experiment with 25, 50, and 75 mg kg⁻¹ Cu, applied alone or in combination with soil-applied EDTA (5 mmol kg⁻¹) or with both EDTA and foliar-applied IAA (5 µmol L⁻¹), growth, physiology, antioxidants, and Cu partitioning/distribution of the selected plants were analyzed.

RESULTS

Significant inhibition occurred in growth, biomass (40% in sunflower; 25% in maize), and photosynthetic pigments (30-35%), along with elevated oxidative stress responses in terms of enzymatic (CAT, APX) and non-enzymatic (flavonoids, phenolics, proline). EDTA alleviated stress by 15-20%, improving growth and pigment retention, while EDTA plus IAA enhanced biomass and pigments by 35-45%, with maize showing the most effective recovery. In remediation, two distinct strategies were identified: maize primarily sequestered Cu in roots (up to 2-fold higher than shoots), reflecting traits suited for phytostabilization, while sunflower efficiently translocated Cu to shoots (translocation factor ~ 3.4), consistent with phytoextraction. The combined application of EDTA and IAA enhanced these inherent strategies. Maize absorbed Cu rapidly at early stages, largely retaining it in roots, whereas sunflower exhibited sustained shoot translocation, highlighting long-term phytoextraction potential.

CONCLUSIONS

These findings move beyond simply reporting amendment efficacy, providing a mechanistic, species-specific framework for selecting plants based on remediation goals, rapid stabilization (maize) versus sustained extraction (sunflower), advancing phytoremediation from trial-and-error approaches toward rational, targeted design.