Sulfur dioxide alleviates programmed cell death in barley aleurone by acting as an antioxidant

Sulfur dioxide (SO(2)), a gaseous signaling molecule in animal cells, has recently been found to play a physiological role in plants. Here we studied the role of SO(2) in gibberellic acid (GA(3))-induced programmed cell death (PCD) in barley (Hordeum vulgare L.) aleurone layers. The application of the SO(2) donor (NaHSO(3)/Na(2)SO(3), 1:3 M/M) effectively alleviated PCD in barley aleurone layers in a dose-dependent manner with an optimal concentration of 50 μM. Further investigations showed that SO(2) reduced the accumulation of hydrogen peroxide (H(2)O(2)), superoxide anion (⋅O(2)(−)) and malondialdehyde (MDA) in aleurone layers. Moreover, the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (POD) were enhanced by SO(2) donor treatment. Meanwhile, lipoxygenase (LOX) activity was attenuated by SO(2) donor treatment. Furthermore, an induction of endogenous H(2)S and NO were also observed in SO(2)-treated aleurone layers, suggesting interactions of SO(2) with other well-known signaling molecules. Taken together, we show that SO(2) negatively regulated PCD by acting as an antioxidant to scavenge excessive reactive oxygen species (ROS) generated during PCD.