The cell wall functions in plant heavy metal response.

Nonessential metals (e.g., cadmium (II), etc) and essential heavy metals (e.g., copper (II), etc) are both toxic for plants at high concentrations. The plant cell wall, which consists of pectin, cellulose, hemicellulose, lignin and proteins, acts as the first barrier for heavy metal ions to enter the cytoplasm. The binding of heavy metal ions within cell wall components is largely determined by the negative charges of functional groups. The cell wall interacts with heavy metal ions through three main mechanisms: ion exchange, chelation models and cell wall remodeling. Various signaling molecules such as nitric oxide and salicylic acid have been implicated in the regulation of cell wall components. An increasing number of reports indicate that microRNAs can target genes related with cell wall synthesis and modification, thereby mediating heavy metal fixation within the cell wall. In this review, we summarize recent advances in understanding the biosynthesis, modifications, and functions of cell wall components under heavy metal stress. We also discuss the interaction mechanisms and the signaling pathways involved in the cell wall-mediated fixation of heavy metals, offering valuable insights into plant heavy metal stress tolerance mechanisms and providing strategic avenues for mitigating heavy metal pollution.