Phytohormone-Mediated Responses of Microalgae to Metal Stress: From Molecular Regulation to Potential Applications in Ecological Remediation

Heavy metal pollution caused by industrial wastewater has posed a severe threat to water ecological security and human health. Traditional treatment technologies are limited by high costs and the risk of secondary pollution. In contrast, microalgal bioremediation technology, which features high efficiency, environmental friendliness, and potential for resource recycling, has emerged as a cutting-edge research focus. This study systematically examines the toxic response mechanisms of microalgae under heavy metal stress, including lipid peroxidation-mediated membrane damage, obstruction of the photosynthetic electron transport chain, competitive inhibition of key enzyme activities, and reactive oxygen species (ROS)-triggered oxidative stress cascades. Furthermore, the tolerance mechanisms of microalgae are thoroughly analyzed, encompassing cell wall adsorption, activation of antioxidant defense systems, regulation of metal transporters, and coordination of phytohormone signaling networks. Phytohormones mitigate heavy metal stress by modulating the expression of cell division-related genes, influencing metal transporter synthesis, enhancing membrane stability, and activating antioxidant enzymes. This study also incorporates multi-omics analyses and discusses the potential of synthetic biology approaches to engineer phytohormone metabolic pathways, with the aim of developing smart, heavy metal-responsive microalgal strains. This provides a systematic framework from fundamental mechanism analysis to applied innovation, promoting the development of microalgal bioremediation technology toward greater precision and intelligence.