Signaling Mechanism Of Sulfur Dioxide Regulating Seed Germination Under Cadmium Stress

As a well-known widespread air pollutant, The high concentration of sulphur dioxide (SO2) would endanger the growth of plant. However, it is to be a signal molecule participating in various biological processes such as regulating the cardiovascular and cerebrovascular and participating in the inflammatory response in animal. But there is limited information on the regulatory role of SO2in plant growth and regulation. In the present study, the role of SO2on wheat seed germination under cadmium (Cd2+) stress was investigated, indicating that wheat(Triticum aestivum L.) seed germination and seedling growth was gradually inhibited with the enhancement of CdCl2stress, the half inhibitory concentration of Cd was1.0mmol/L. The inhibitory effect of Cd2+stress on seed germination was substantially alleviated by pre-treatment with the SO2donor Na2SO3/NaHSO3(3:1). The role of SO2donor in counteracting CdCl2-induced stress was in a dose-dependent manner with the most optimal concentration of1.5mmol/L. We also found that SO2donor provided favorable conditions for the growth of wheat seeds by promoting the activities of amlase and easterase and improving the count of soluble sugar and protein under Cd-stress.Cadmium stress caused the burst of reactive oxygen species. Further investigation showed SO2donor-pretreated promoted the activities of superoxide, dismutase (SOD), guaiacol peroxidase(POD), catalase(CAT) and ascorbate peroxidase(APX), inhibited lipoxygenase (LOX) activity significantly, overproduced the·O2-, H2O2and MDA content and protected the integrity of plasma membrane in the germination of wheat seeds under cadmium stress. These data indicated that SO2was involved in the antioxidant mechanism on seed germination against Cd2+stress. In addition, SO2-pretreated caused the rapid burst of endogenous H2S in the early germination of wheat seeds, it showed that endogenous H2S was involved in antioxidant system in wheat seeds.Aleurone programmed cell death (PCD) accompanied with seed germination. As endogenous signaling molecles, ABA and GA play a key role in dormancy formation and dissolution of seed germination. ABA stoped embryo cell division, and GA promote seed germination, both of them are antagonistic relationship mutually in regulating seed dormancy and germination. we explored whether SO2and H2S participated in programmed cell death (PCD) in the aleurone cells in the seed of soybean and barley. The reults showed SO2(1.0mmol/L) and NaHS (H2S donor) treatment delayed the aging of the aleurone cells. Further testing found that H2S can delay the GA-mediated apoptosis of barley within a certain concentration range, and had no significant effect on ABA in wheat and soybean aleurone cells.