Sulfur containing air pollutants and their effects on plant metabolism

H2S and SO2 affected plant yield at relative low levels without causing visible injury. In general H2S was more toxic than SO2. Short-term exposure (24 to 48 h) of plants to the pollutants affected sulfur, nitrogen and energy metabolism. Both exposure of plants to H2S and SO2 resulted in an accumulation of glutathione in the leaves; this accumulation was higher in H2S than in SO2 exposed plants. SO2 exposure resulted in a rapid accumulation of sulfate, which was absent in H2S exposed plants. Amino acid metabolism in spinach leaves was strongly affected by short-term H2S exposure. Besides a strong increase in the cysteine content, there was a substantial decrease in the serine content. The content of most other amino acids and ammonia increased upon exposure, which indicated an overall effect of H2S on amino acid/protein metabolism. In vivo nitrate reductase activity measured under aerobic conditions was increased in H2S exposed spinach leaves. Leaf respiration was not affected by H2S exposure. NADH oxidation by other cytosolic enzymes was inhibited in H2S exposed plants, and the level of inhibition correlated with the reduction in relative growth rate by H2S