Uniconazole confers chilling stress tolerance in soybean (Glycine max L.) by modulating photosynthesis, photoinhibition, and activating oxygen metabolism system

The current study investigates a possible mediatory role of uniconazole in improving chilling stress tolerance in chilling-sensitive (Hefeng 50) and chilling-tolerant (Kenfeng 16) soybean varieties. Chilling stress decreased photosynthetic pigments and inhibited net photosynthetic rate which was ascribed to stomatal limitation. The maximum quantum efficiency of PSII primary photochemistry and electron transport rate were lower in uniconazole-treated plants compared with the control. The increased contents of superoxide (O-2(center dot-)) and malondialdehyde during chilling stress indicated oxidative stress. Chilling stress reduced glutathione and ascorbic acid contents, and promoted peroxidase, glutathione reductase, and ascorbate peroxidase activities. Uniconazole improved the tolerance of chilled plants. This might be due to better antioxidant defense mechanisms including higher contents of antioxidants and activities of antioxidant enzymes, which retard lipid peroxidation. Thus, uniconazole has a positive effect and improves the chilling resistance of soybean.