Abstract: Mercury (Hg) is highly toxic. Rice (Oryza sativaL.) is one of the most important pathways for Hg exposure to populations. To reveal the molecular mechanism of rice adaptation to Hg stress, the Jinyou 431 rice cultivar grown under supplementation of 0 mg·kg^-1 (CK), 50 mg·kg^-1 (low), 150 mg·kg^-1 (middle), and 300 mg·kg^-1 (high) HgCl₂ was selected to investigate root tips’ differentially expressed proteins in response to Hg stress using the isotope relative labeling and the absolute quantitative technique TMT (Tandem Mass Tag) combined with parallel reaction monitoring (PRM) quantitative proteomic technique. Bioinformatics analysis of the obtained differential proteins was performed to screen the target proteins responding significantly to Hg stress. A total of 20 differentially expressed proteins identified were selected for protein validation. The results showed that 5253 quantitative proteins and 364 differential proteins were identified (variation fold≥1.3, P<0.05), out of which 258 were up-regulated and 106 downregulated. The molecular function of gene ontology suggests that differential proteins are mainly involved in catalytic activity, binding transport activity, and antioxidant activity. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway significantly enriches in metabolic pathways, secondary metabolite biosynthesis, and phenylpropanoid biosynthesis (with false discovery rates of <0.05). The identified and validated differential proteins are related to antioxidant reductase, metal chelate peptide synthesis protein, and metallothioneinrelated proteins like. The expression levels of proteins involved in responding and signaling pathway to antioxidants and heavy metal stress defense were generally up-regulated, while the expression levels of those involved in metabolism, energy production and transport were generally down regulated.

Key words: 24-epibrassinolide, low light stress, tomato, morphology, photosynthetic performance.