The Enhancement of Drought Tolerance in Arabidopsis Plants Induced by Pretreatment with Sulfur Dioxide
Abstract Sulfur dioxide (SO2) is a common air pollutant that has multiple effects on plants. Here, the effect of prior exposure to SO2 on the improvements of drought tolerance and possible regulation mechanisms were investigated in Arabidopsis plants. The experimental results showed that pre-exposure to 30 mg/m3 SO2 for 72 h could reduce leaf water loss, and enhance the drought tolerance of Arabidopsis plants. SO2 pre-exposure decreased leaf stomatal conductance (Gs) and transpiration rate (Tr) but increased net photosynthetic rate (Pn), water use efficiency (iWUE) and photosynthetic pigment contents under drought conditions. Importantly, the activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly increased, while the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) were decreased in SO2-pretreated Arabidopsis plants under drought stress. Additionally, the activity of o-acetylserine(thio)lyase (OASTL) and the content of cysteine (Cys), the rate-limiting enzyme and the first organic product of sulfur assimilation, were increased significantly in drought-stressed plants after SO2 pretreatment, along with the increases of other thiol-containing compounds glutathione (GSH) and non-protein thiol (NPT). Meanwhile, SO2 pre-exposure induced a higher level of proline accumulation, accompanied by the increased activity of proline synthase P5CS, the decreased activity of proline dehydrogenase ProDH and the corresponding alteration of gene transcription. Collectively, the enhanced drought tolerance afforded by SO2 might be related to the improvement of plant photosynthesis, antioxidant defense, sulfur assimilation and osmotic adjustment. These findings provide new insights in understanding the role of SO2 in plant adaptation to environmental stress.