Effects of ethylene and NO on AsA-GSH in lotus under cadmium stress

Under the background of Cd (50 μmol·L^-1) stress, we added ethylene precursor ACC (100 μmol·L^-1), ACC + nitric oxide synthase (NOS) inhibitor L-NNA (200 μmol·L^-1), ACC + nitrate reductase (NR) inhibitor Tu (1 mmol·L^-1), ACC + nitric oxide (NO) scavenger PTIO (200 μmol·L^-1), NO donor SNP (500 μmol·L^-1), SNP + ethylene signal inhibitor STS (100 μmol·L^-1) to examine their effects on the damage degree of leaves and response mechanisms of AsA-GSH cycle in lotus 'Weishanhuhonglian'. Results showed toxic symptom of lotus leaves under Cd stress. The relative conductivity, malondialdehyde (MDA), as well as ascorbic acid (AsA) and glutathione (GSH) contents were significantly increased, but the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were obviously decreased. Compared with Cd stress, adding ACC significantly increased the damage area of lotus leaves, decreased activities of the above-mentioned four antioxidant enzymes and increased AsA and GSH contents. SNP aggravated the toxic symptom of lotus leaves and decreased GR and MDHAR activities. PTIO significantly relieved the toxic symptom of leaves, increased activities of APX, GR, MDHAR and DHAR, but decreased AsA and GSH contents compared with Cd and ACC treatment. However, the effects of L-NNA and Tu were not as obvious as PTIO's. In comparison with Cd and SNP treatment, STS relieved the toxic symptom of leaves, increased APX, GR, MDHAR and DHAR activities, and decreased AsA and GSH contents. Taken together, these results showed the synergistic effects of ethylene and NO in regulating lotus responses to Cd stress through AsA-GSH cycle.