Differences in detoxification mechanism and gene expression changes of sulfur metabolism in coping with the air pollutant SO2 between the resistant and ordinary poplar variety

In this study, two poplar varieties with different resistance to sulfur dioxide were selected for a comparative experiment. SO2 fumigation to the poplars was carried out under controlled conditions to determine the variation in the activity of enzymes, the content of metabolites and the expression of enzymes genes in pathways of sulfur metabolism in plants. The results showed that the activity of enzymes and the content of sulfur metabolites were closely related to the response of the poplars to SO2 stress. Populus x euramericana cv. 'Purui' had two ways of detoxification: oxidation detoxification, oxidizing sulfite (SO32-) to sulfate SO42- by sulfite oxidase; reductive detoxification, SO32- being reduced to S2- by sulfite reductase (SiR). Moreover, OASTL and SAT activity, and levels of cysteine (CYS) and glutathione (GSH) also increased in P. x euramericana cv. 'Purui' in response to SO2 fumigation, and the gene expression encoding Glutathione S-transferases (GST), and some enzymes in cysteine and methionine metabolism was up-regulated. For Populus x euramericana cv. '74/76' with weaker resistance to sulfur dioxide, it only detoxified by increasing the activity of SiR, and but down-regulated the expression of gene encoding 3'-phosphoadenosine 5'-phosphosulfate synthase (PAPSS), which could affect the consumption of sulfite in the exposure to SO2. Thus, the SO2-resistant difference of the two poplar varieties is mainly attributed to variation in activity of the enzymes and content of their metabolites in pathways of sulfur metabolism, and gene expression of some enzymes in cysteine and methionine metabolism also plays a role in the resistant difference.

Automated summary

The study compared two poplar varieties with different resistance to sulfur dioxide, finding that the variation in enzyme activity and metabolite content in sulfur metabolism pathways played a key role in their resistance difference. The 'Purui' variety detoxified sulfur dioxide through two pathways, while the '74/76' variety only increased the activity of SiR for detoxification. Additionally, gene expression of enzymes in cysteine and methionine metabolism also contributed to the resistance difference.