Lead Toxicity Regulation Via Protein Degradation and Tetrapyrrole Biosynthesis Pathways in Brassica Species: A Comparative Quantitative Analysis of Proteomic Study.

Understanding the heavy metals (HMs) tolerance mechanism is crucial for improving plant growth in metal-contaminated soil. In order to evaluate the lead (Pb) tolerance mechanism in Brassica species, a comparative proteomic study was used. Thirteen-day-old seedlings of B. juncea and B. napus were treated with different Pb(NO3)2 concentrations at 0, 3, 30, and 300 mg/L. Under 300 mg/L Pb(NO3)2 concentration, B. napus growth was significantly decreased, while B. juncea maintained normal growth similar to the control. The Pb accumulation was also higher in B. napus root and shoot compared to B. juncea. Gel-free proteomic analysis of roots revealed a total of 68 and 37 differentially abundant proteins (DAPs) in B. juncea and B. napus-specifically, after 300 mg/L Pb exposure. The majority of these proteins are associated with protein degradation, cellular respiration, and enzyme classification. The upregulated RPT2 and tetrapyrrole biosynthesis pathway-associated proteins maintain the cellular homeostasis and photosynthetic rate in B. juncea. Among the 55 common DAPs, S-adenosyl methionine and TCA cycle proteins were upregulated in B. juncea and down-regulated in B. napus after Pb exposure. Furthermore, higher oxidative stress also reduced the antioxidant enzyme activity in B. napus. The current finding suggests that B. juncea is more Pb tolerant than B. napus, possibly due to the upregulation of proteins involved in protein recycling, degradation, and tetrapyrrole biosynthesis pathway.