Antioxidant defenses against air humidity stress in fruit body of Auricularia heimuer

Air humidity is an important environmental factor restricting the fruit body growth of Auricularia heimuer. Low air humidity causes the fruit body to desiccate and enter dormancy. However, the survival mechanisms to low air humidity for fruit bodies before dormancy remain poorly understood. In the present study, we cultivated A. heimuer in a greenhouse and collected the fruit bodies at different air humidities (90%, 80%, 70%, 60%, and 50%) to determine the contents of malondialdehyde (MDA) and non-enzymatic antioxidants such as ascorbic acid (AsA) and glutathione (GSH); and the activities of enzymatic antioxidants including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and glutathione reductase (GR). Results showed that the MDA contents had a tendency to increase with decreasing relative air humidity. Relative air humidity below 90% caused membrane lipid peroxidation and oxidative stress (based on MDA contents) to the fruit body, which we named air humidity stress. In contrast to the control and with the degree of stress, the GSH contents and activities of SOD, CAT, GR, GPX, and APX tended to ascend, whereas AsA showed a declining trend; the POD activity only rose at 50%. The antioxidants favored the fruit body to alleviate oxidative damage and strengthened its tolerance to air humidity stress. The antioxidant defense system could be an important mechanism for the fruit body of A. heimuer in air humidity stress.