Methane protects against polyethylene glycol-induced osmotic stress in maize by improving sugar and ascorbic acid metabolism

Although aerobic methane (CH4) release from plants leads to an intense scientific and public controversy in the recent years, the potential functions of endogenous CH4 production in plants are still largely unknown. Here, we reported that polyethylene glycol (PEG)-induced osmotic stress significantly increased CH4 production and soluble sugar contents in maize (Zea mays L.) root tissues. These enhancements were more pronounced in the drought stress-tolerant cultivar Zhengdan 958 (ZD958) than in the drought stress-sensitive cultivar Zhongjiangyu No.1 (ZJY1). Exogenously applied 0.65 mM CH4 not only increased endogenous CH4 production, but also decreased the contents of thiobarbituric acid reactive substances. PEG-induced water deficit symptoms, such as decreased biomass and relative water contents in both root and shoot tissues, were also alleviated. These beneficial responses paralleled the increases in the contents of soluble sugar and the reduced ascorbic acid (AsA), and the ratio of AsA/dehydroascorbate (DHA). Further comparison of transcript profiles of some key enzymes in sugar and AsA metabolism suggested that CH4 might participate in sugar signaling, which in turn increased AsA production and recycling. Together, these results suggested that CH4 might function as a gaseous molecule that enhances osmotic stress tolerance in maize by modulating sugar and AsA metabolism.