Age-Dependent Differences in Leaf Sulfur Assimilation and Relationship with Resistance to Air Pollutant SO2

Two poplar varieties with different resistance to sulfur dioxide were subjected to different concentrations of SO2 fumigation treatment. Young and mature leaves of Purui poplar (resistant) vs. 74/76 poplar (susceptible) were used to measure the changes in the activity of enzymes and metabolite content. Among the five key enzymes involved in sulfur metabolism and sulfur metabolites, APR, SO enzyme, GSH, and sulfate content have the greatest impact on young leaves of Purui, followed by 74/76 young leaves. The results show that for both Purui and 74/76 poplar, young leaves have stronger sulfur metabolism ability than mature leaves, indicating that young leaves have stronger SO2 resistance. Purui has stronger sulfur metabolism ability than 74/76 poplar, especially reflected in their young leaves. The comparison between young and mature leaves, as well as the comparison between resistant and susceptible varieties, mutually confirms that sulfur metabolism in leaves is an important mechanism for sulfur dioxide resistance.