Physiological Adaptation to Different Heavy Metal Stress in Seedlings of Halophyte Suaeda liaotungensis

Soil contamination with heavy metals is a worldwide environmental issue that impacts plant growth and human health. This study is the first to investigate the tolerance and physiological response mechanism of <i>Suaeda liaotungensis</i> seedlings to heavy metal stress. The results exhibited that the toxicity degree of Pb, Cd, Cu, and Zn to <i>Suaeda liaotungensis</i> seedlings was highest for Cd and lowest for Pb. Heavy metal stress increased H₂O₂ levels in seedlings, thereby aggravating lipid peroxidation of the cell membrane and consequently increasing MDA content. Meanwhile, the SOD and CAT activities in seedlings increased under heavy metal stress, whereas POD activity decreased consistently under Cd and Zn stress. The soluble sugars and proline content in seedlings also showed an increasing trend under heavy metal stress. Furthermore, the tolerance in the seedlings from black seeds to Pb and Cd stress was improved by enhancing SOD and CAT activities and accumulating proline. However, the tolerance in the seedlings from brown seeds to Cu stress was improved by increasing CAT activity as well as accumulating soluble sugar and proline content. The results reveal the response mechanism of <i>Suaeda liaotungensis</i> seedlings to heavy metal stress and provide the basis for utilizing <i>Suaeda liaotungensis</i> to improve heavy metal-contaminated saline soil.