Adaptive responses of Alternanthera tenella Colla. to cadmium stress through physiology, elemental allocation and morpho-anatomical modifications

Abstract

Industrialization has accelerated the rate of heavy metal discharge into the environment and among trace metals, cadmium (Cd) gains attention due to its relative mobility from soil to plant and potential toxicity to humans. Phytoremediation is a plant-based, cost-effective approach to remediate the contaminated soil and water, and an attempt has been made in the present study to explore the potential of an invasive plant Alternanthera tenella for Cd removal. The physiological and morpho-anatomical modifications of plant tissues including the elemental allocation pattern and bioaccumulation potential were studied in response to 170 µM of Cd(NO₃)₂. Cd negatively affects the growth parameters, biomass, and photosynthetic efficacy of the plant. Cd treatment influenced the distribution of macro and microelements in the plant and the structural moieties in the biomolecules on the interaction of metal ions. Anatomical modifications included the alterations in the diameter and thickness of cell walls, especially xylem walls, the presence of cell structural distortions and blockage, and fully opened stomata with thick guard cells and depositions. Metabolites like proline, flavonoids, phenol, and malondialdehyde marked a significant increase in stress tolerance. Despite having a relatively low transfer factor (TF), A. tenella exhibits high values of biological concentration factor (BCF) and biological accumulation factor (BAF), suggesting its suitability for phytostabilization of Cd-contaminated environments.