Sulfur Dioxide Enhances Endogenous Hydrogen Sulfide Accumulation and Alleviates Oxidative Stress Induced by Aluminum Stress in Germinating Wheat Seeds

Aluminum ions are especially toxic to plants in acidic soils. Here we present evidences that SO(2) protects germinating wheat grains against aluminum stress. SO(2) donor (NaHSO(3)/Na(2)SO(3)) pretreatment at 1.2 mM reduced the accumulation of superoxide anion, hydrogen peroxide, and malondialdehyde, enhanced the activities of guaiacol peroxidase, catalase, and ascorbate peroxidase, and decreased the activity of lipoxygenase in germinating wheat grains exposed to Al stress. We also observed higher accumulation of hydrogen sulfide (H(2)S) in SO(2)-pretreated grain, suggesting the tight relation between sulfite and sulfide. Wheat grains geminated in water for 36 h were pretreated with or without 1 mM SO(2) donor for 12 h prior to exposure to Al stress for 48 h and the ameliorating effects of SO(2) on wheat radicles were studied. SO(2) donor pretreatment reduced the content of reactive oxygen species, protected membrane integrity, and reduced Al accumulation in wheat radicles. Gene expression analysis showed that SO(2) donor pretreatment decreased the expression of Al-responsive genes TaWali1, TaWali2, TaWali3, TaWali5, TaWali6, and TaALMT1 in radicles exposed to Al stress. These results suggested that SO(2) could increase endogenous H(2)S accumulation and the antioxidant capability and decrease endogenous Al content in wheat grains to alleviate Al stress.