Silicone Alleviates Palladium Toxicity by Modifying Palladium Uptake, Ascorbate-Glutathione Cycle, and Glyoxalase System in Maize Seedlings

Palladium (Pd) is a trace metal used in automotive catalytic converters, which has adverse effects on living organisms when migrating into the environment. Silicon (Si) is an element that ameliorates the toxicity of metals and is abundant in the earth's crust. In the present study the effect of Si and Pd on plant growth, ascorbate-glutathione cycle (ASA-GSH), and glyoxalase system in maize were investigated. Pd stress decreased growth, chlorophyll content, and leaf relative water content, increased Pd concentration in maize seedlings. Si treatment alleviated Pd toxicity by improving growth and chlorophyll content, decreasing Pd content in roots and leaves. Besides, Si also induced the accumulation of soluble sugars, soluble proteins, and proline. Pd stress enhanced reactive oxygen species (ROS), malondialdehyde (MDA), and methylglyoxal (MG) levels. Si application modulated ascorbate and glutathione levels, ASA-GSH cycle enzyme activities, glyoxalase I and glyoxalase II activities, superoxide dismutase, and catalase activities, and resulted in a considerable reduction in ROS, MDA, and MG levels during Pd stress. Moreover, the expression of ascorbate peroxidase, catalase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase genes was induced in the presence of Si to alleviate Pd stress. The results indicated that Si treatment improved tolerance to Pd in maize by regulating growth, Pd uptake, ASA-GSH cycle, and glyoxalase system.