Changes in the Activity and Transcription of Antioxidant Enzymes in Response to Al Stress in Black Soybeans

In this study, the effects of Al stress on the activity and transcription of antioxidant enzymes were investigated in an acid-resistant black soybean (RB) and an acid-sensitive black soybean (SB) under hydroponic conditions to further clarify the role of antioxidant enzymes in the plant's response to Al stress. The results indicated that oxidative stress was induced in the roots and leaves of RB and SB and that the stress level was higher in SB than in RB. Changes in the catalase (CAT) activity in response to Al stress occurred faster in RB roots and leaves than in SB. As the duration of Al stress increased, the peroxidase (POD) activity was enhanced more pronouncedly in RB roots and leaves than in SB. The activity of superoxide dismutase (SOD) in the roots and leaves of RB and SB was not responsive to Al stress. A high transcription level of a selected POD gene was detected in RB leaves, but no transcription of this POD gene was observed in SB leaves under Al stress. Moreover, the transcription level of this POD gene was higher in RB roots than in SB roots. Under Al stress, the transcription of two selected SOD genes showed an increasing trend in RB but decreased in SB. Furthermore, the transcription levels of these two selected SOD genes were always higher in RB than in SB. The above results suggest that not only does RB have a higher level of antioxidant enzyme activities but also that antioxidant enzyme genes can be upregulated by Al stress. This may be an important mechanism for RB to deal with oxidative stress induced by Al toxicity.