Heavy metals and ethylene: shaping plant responses through signaling

Heavy metal (HM) contamination is an escalating global issue, significantly affecting crop quality and productivity, and this problem is further exacerbated by rapid population growth. HMs impact plant productivity by interfering with a range of morphologic, biochemical, physiologic, and molecular functions, as documented in numerous studies. Upon entry into plant cells, these metals compromise cell membrane integrity, induce reactive oxygen species production in excess, disrupt enzymatic activities, damage photosynthetic pigments and photosystems, and disturb water and nutrient uptake mechanisms. Within the cellular environment, several signaling pathways are either activated or repressed, adjusting cellular responses in accordance with their genetic potential. Phytohormones are key regulators in these processes, utilizing signaling cascades such as mitogen-activated-protein-kinase and calcium dependent pathways. Among them, ethylene, traditionally known for its role in exhibiting critical role in modulating plant responses to HM stress. This review focuses on ethylene's interaction under HM stress, examining its crosstalk with other plant hormones. In addition, it explores HM sources, bioavailability, implications for human health, plant responses to HM exposure, and the influence of ethylene biosynthesis and signaling pathways in the regulation of HM-induced stress responses.