High sulfate exacerbates heavy metal toxicity in Chinese cabbage (Brassica chinensis L.) by impairing plant ROS scavenging in heavy metals contaminated soil

Accumulation of heavy metals (HMs) and sulfates in farmland near mines is one of the most serious environmental problems posing a threat to crops and human health. Moderate sulfate alleviates the toxicity of HMs in crops, but the impact of high sulfate on crops in HM-contaminated soil remains unclear. Hence, we integrated physiological, transcriptomic and metabolomic profiling to investigate the effect of high sulfate on Chinese cabbage (Brassica chinensis L.) under HMs through controlled pot experiments. According to our results, compared with the HMs only group, the growth indicators of Chinese cabbage in the HMs plus high sulfate group decreased by 11.94% to 49.19%, and photosynthesis was significantly inhibited (p < 0.05). Notably, potential biomarkers indicating high sulfate were identified: catalase, fructose-bisphosphate aldolase 2, senescence-associated gene 21, ferritin-1, and 2-Aminoadipic acid. Mechanistically, high sulfate intensified oxidative damage by suppressing the synthesis of glutathione (with a 43.43% reduction) and γ-aminobutyric acid (with a 15.19% decline), consequently resulting in a 21.79% increase in reactive oxygen species (ROS) within the leaves. The excessive accumulation of ROS appeared to directly initiate programmed cell death, induced cellular damage in roots and leaves, and might enhance autophagic degradation of chloroplasts and the endoplasmic reticulum. Then, photosynthesis, sucrose synthesis, amino acid anabolism, and energy production pathways were disrupted, leading to the further reduction of Chinese cabbage biomass. Consequently, this study emphasized the harmful effects of high sulfate on Chinese cabbage in HM-contaminated soil through disrupting the ROS clearance function of Chinese cabbage.