Abstract:

【Objective】 The aim of this study was to investigate effects of waterlogging stress on the ascorbate-glutathione (AsA-GSH) cycle of soybean leaves and the regulating effect of uniconazole (S3307) during initial flowering stage (R1), so as to provide a theoretical basis for improving soybean waterlogging resistance and the application of uniconazole.【Method】 This study was conducted in the pot plant of the National Coarse Grain Engineering Technology Research Center of Bayi Agricultural University in Heilongjiang in 2019. The water-tolerant variety KenFeng 14 and the waterlogging-sensitive variety KenFeng 16 were used as test materials for pot planting experiments. The leaves were sprayed with S3307 (concentration 50 mg·L^-1, appropriate spray amount 225 L·hm^-2). After spraying S3307 for 5 days, the waterlogging stress treatment was started after 0 d (R1+5) and 5 d (R1+10) and normal water treatment for 5 days (R1+15) after sampling, respectively, and the various physiological indicators were measured by using spectrophotometer to study the degree of membrane lipid peroxidation (MDA) of soybean leaves under waterlogging stress. The effects of reactive oxygen species (ROS) and non-enzymatic antioxidants (AsA, DHA, GSH, and GSSG) and key enzymes (APX, GR, MDHAR, and DHAR) in the AsA-GSH circulatory system and the mitigating effects of S3307 were analyzed. 【Result】 In the R1 stage after R1+5 of waterlogging stress, compared with CK, the S3307 treatment reduced the MDA, $\mathop{{O}}_{2}^{{\mathop{}_{\ ·}^{-}}}$ production rate and H₂O₂ content, and also increased the content of non-enzyme antioxidants and key enzymes in the AsA-GSH cycle to maintain ROS balance, thus promoted the growth and development of two soybean varieties. At R1+10, W treatment significantly increased the MDA content in the leaves of the two soybean varieties, which were significantly increased by 40.02% and 37.53% higher than that of CK, respectively, and accelerated ROS ($\mathop{{O}}_{2}^{{\mathop{}_{\ ·}^{-}}}$ and H₂O₂); the $\mathop{{O}}_{2}^{{\mathop{}_{\ ·}^{-}}}$ production rate of the two varieties under waterlogging stress was significantly increased by 60.29% and 27.77%, compared with CK, respectively; The H₂O₂ content was significantly increased by 49.45% and 43.40% compared with CK, respectively; The waterlogging sensitive variety KenFeng 16 suffered more damage than the waterlogging resistant variety KenFeng 14, and at the same time, under the waterlogging stress, the antioxidant substances and key enzyme activities in the leaves of both soybean varieties were increased to adapt to the waterlogging stress response from stress. After S3307 treatment, W+S treatment could further increase antioxidant substances (AsA, GSH), redox substances (DHA, GSSG), total ascorbic acid (AsA + DHA) and total glutathione (GSH +GSSG) content under waterlogging stress.content, and increase the activity of antioxidant enzymes (APX, GR, MDHAR, DHAR), reduce the MDA content of the leaves, inhibit the accumulation of ROS, and reduce the damage caused by waterlogging stress to the membrane system. After returning to normal water treatment for 5d (R1 + 15), the above indexes of two soybean varieties W treatment were reduced, but W+S treatment could maintain the two soybean leaves. The higher antioxidant enzyme activity and antioxidant substance content accelerated the removal of excessive accumulation of MDA and ROS, promoted the AsA-GSH cycle operation in soybean leaves under waterlogging stress, and then promoted the return of the two soybean varieties to normal state.【Conclusion】 Waterlogging stress had different degrees of influence on membrane lipid peroxidation, ROS accumulation, and key enzyme activities and non-enzyme antioxidants in the AsA-GSH cycle of soybean leaves. Spraying S3307 could improve key enzyme activity at some extent to promote oxidation ability, so as to reduce the harm caused by waterlogging stress.

Key words: soybean, waterlogging stress, AsA-GSH cycle, leaves, uniconazole