Molybdenum (Mo) has been reported to alleviate drought stress by enhancing antioxidant defense in plants, but the underlying mechanism remains unclear. Here, we hypothesized that Mo mediates nitric oxide (NO)-induced antioxidant defense through Mo-enzymes, particularly by nitrate reductase (NR) in wheat under drought stress. The 30-day-old wheat seedlings cultivated in -Mo (0 μM Mo) and +Mo (1 μM Mo) Hoagland solutions were detached and then pretreated with Mo-enzyme inhibitors, NO scavengers, NO donors or their combinations according to demands of complementary experiment under 10% polyethylene glycol 6000 (PEG)-stimulated drought stress (PSD). Mo supplementation increased the activities and transcripts of antioxidant enzymes, decreased H2O2 and MDA contents, and elevated NO production, implying that Mo-induced antioxidant defense may be related to NO signal. Complementary experiment showed that NO production was induced by Mo, while suppressed by Mo-enzyme inhibitors and NO scavengers, but restored by NO donors, suggesting that Mo-induced increase of NO production may be due to the regulation by Mo-enzymes. Further experiment indicated that the increased activities and transcripts of antioxidant enzymes induced by Mo were suppressed by Mo-enzyme inhibitors and NO scavengers, and NO donors could eliminate their suppressing effects. Moreover, Mo application increased NR activity and inhibitors of Mo-enzymes inhibited NR activity in wheat leaves under PSD, suggesting that NR might involve in the regulation of Mo-induced NO production. These results clearly indicate that NO mediates Mo-induced antioxidant defense at least partially through the regulation of NR.
Keywords: Molybdenum; antioxidant defense; drought stress; nitrate reductase; nitric oxide; winter wheat.