Biochemical and proteomic analyses explain the role of thiourea in improving tolerance against cadmium toxicity in maize

Thiourea (TU), a sulfur-containing compound, is recognized for its ability to ameliorate the deleterious impacts of metal ions on plant growth. Nonetheless, the molecular mechanisms by which TU regulates metabolic activities in maize (Zea mays L.) under cadmium (Cd) stress remain largely unexplored. This study seeks to clarify how TU (35 μM) mitigates or enhances tolerance to Cd toxicity (50 μM) through physiological and proteomic methods. Cd exposure resulted in inhibited plant growth, leaf chlorosis, and lipid peroxidation; however, the addition of TU reduced Cd toxicity by decreasing Cd accumulation and modulating antioxidant enzyme activity. The global proteome profile was significantly affected by Cd stress, regardless of TU supplementation. Using a gel-free proteomic approach (nLC-MS/MS), we identified a total of 3,213 proteins, of which 1,573 were differentially expressed proteins (DEPs) in response to Cd and/or TU+Cd treatments compared to the control. Among these, 1,237 proteins were up-regulated, while 336 were down-regulated. Gene ontology (GO) analysis indicated that many DEPs were associated with the citrate cycle, photosynthesis, glutathione metabolism, and various metabolic pathways. Notably, proteomic analysis revealed that TU notably enhanced the expression of proteins linked to photosynthetic electron transfer when subjected to Cd stress. Key candidate proteins including glutathione S-transferase, monodehydroascorbate reductase, peroxidase, chaperonin, Hsp70-Hsp90 organizing protein, proteasome subunits, and ubiquitin-related proteins were identified as vital players in the antioxidant defense system and protein metabolism facilitating Cd detoxification in maize. Collectively, these results offer valuable insights into the mechanisms by which TU mitigates Cd toxicity in maize.