Sulfur dioxide acts as an antioxidant and delays programmed cell death in wheat aleurone layers upstream of H2S and NO signaling pathways

Sulfur dioxide is a widespread air pollutant and it also acts as a signaling molecule in various processes in mammals. However, the role of SO2 in programmed cell death (PCD) in plants is unclear. Here we studied the role of SO2 in gibberellin (GA)-treated wheat aleurone layers. The results showed that 100 μM SO2 donor (NaHSO3/Na2SO3) could effectively delay PCD and inhibit the coalescence of small protein storage vacuoles (PSVs) in aleurone cells treated with GA. Also, SO2 could reduce the accumulation of hydrogen peroxide and superoxide anion in GA-treated aleurone layers. In this process, SO2 could sustain higher activities of catalase, guaiacol peroxidase, ascorbate peroxidase, and superoxide dismutase and lower activities of lipoxygenase and polyphenol oxidase by comparing with GA alone. In addition, an induction of endogenous H2S and NO was observed in SO2-treated aleurone layers. The application of NO scavenger cPTIO could accelerate PCD in SO2 or H2S treated aleurone cells, suggesting that NO alleviated PCD by acting downstream of SO2 and H2S. In conclusion, these results imply that SO2 could delay PCD in GA-treated wheat aleurone layers by enhancing cellular antioxidative capacity, and H2S/NO signals act downstream of SO2.