Differences in detoxification mechanism and gene expression changes of sulfur metabolism in coping with the air pollutant SO 2 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. SO 2 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 SO 2 stress. Populus × euramericana cv. 'Purui' had two ways of detoxification: oxidation detoxification, oxidizing sulfite (SO 3 2− ) to sulfate SO 4 2− by sulfite oxidase; reductive detoxification, SO 3 2− being reduced to S 2− by sulfite reductase (SiR). Moreover, OASTL and SAT activity, and levels of cysteine (CYS) and glutathione (GSH) also increased in P. × euramericana cv. 'Purui' in response to SO 2 fumigation, and the gene expression encoding Glutathione S-transferases (GST), and some enzymes in cysteine and methionine metabolism was up-regulated. For Populus × 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 SO 2 . Thus, the SO 2 -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.