Responses of the Antioxidant Defense System to Drought Stress in the Leaves of Fargesia denudata Seedlings, the Staple Food of the Giant Panda1

The responses of the antioxidant defense system in plant species to drought stress are still relatively unknown. In order to further understand how the system responds to drought stress, the leaves of Fargesia denudata seedlings were investigated. Antioxidant enzyme activities, antioxidant contents, hydrogen perox ide (H2O2), superoxide anion ( ) and MDA contents in the seedling leaves were measured under well watered (WW), moderate drought stressed (MD), and severe drought stressed (SD) treatments. Although drought stress significantly increased H2O2 and levels in F. denudata leaves, only weak lipid peroxidation was observed. This is attributed to the higher superoxide dismutase (SOD), catalase (CAT), ascorbate perox idase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascor bate reductase (DHAR) activities in F. denudata leaves during the entire drought period. Reduced and oxi dized ascorbate (AsA and DHA) contents were almost not affected by drought except that DHA under SD showed an obvious increase on day 30. Furthermore, reduced glutathione (GSH) content under drought stress significantly decreased, while oxidized glutathione (GSSG) markedly increased under SD on days 30 and 45 as well as under MD on day 30; as a result, the ratio GSH/GSSG declined considerably. These results indicated that GSH was involved in scavenging H2O2 and under drought stress and it was more sensitive to drought stress in scavenging H2O2 and than AsA. As a result, a highly efficient antioxidant defense system in drought stressed F. denudate leaves operated mainly through the synergistic functioning of SOD, CAT, APX, MDHAR, DHAR, GR, and GSH against oxidative damage.