Role of Polyamines in Plant Tolerance to Metal Toxicity: A Systematic Review and Meta-Analysis

This meta-analysis combined the results of 61 independent studies published in 2005–2025 to examine polyamine-mediated responses to aluminum, cadmium, lead, chromium, copper, manganese, and selenium stress in plants. The logarithm ratio of responses (lnRR) under the random-effects model was used to calculate the effect sizes. Polyamine application significantly (p < 0.001) enhanced plant growth, with strong increases in root elongation (lnRR = 0.490, 95% CI: 0.362–0.618), fresh weight (lnRR = 0.413, 95% CI: 0.347–0.480), and dry weight (lnRR = 0.475, 95% CI: 0.409–0.541). Oxidative stress was markedly reduced, as reflected by decreases in reactive oxygen species accumulation (lnRR = −0.585, 95% CI −0.682 to −0.487, p < 0.001), hydrogen peroxide content (lnRR = 0.005, 95% CI −0.244 to 0.254, p = 0.968), and lipid peroxidation (lnRR = −0.487, 95% CI −0.578 to −0.397, p < 0.001). The antioxidant defenses were strengthened, and the levels of superoxide dismutase (lnRR = 0.468, p < 0.001) and catalase activity (lnRR = 0.373, p < 0.001) increased significantly. Metal accumulation was consistently reduced in polyamine-treated plants (lnRR = −0.392, 95% CI −0.460 to −0.324, p < 0.001). Supplementary genetic-level data indicated that metal stress triggers polyamines to regulate metal transporters, polyamine biosynthesis genes, antioxidant-related genes, and hormone-signaling pathways. Collectively, these data points make polyamines a key controller of plant metal stress tolerance and offer a quantitative and mechanistic system to apply them to metal-impacted agroecosystems.