Cadmium stress tolerance in wheat seedlings induced by ascorbic acid was mediated by NO signaling pathways

Ascorbic acid (AsA) and nitric oxide (NO) are well known and widespread antioxidants and gaseous molecules that regulate plant tolerance to several stresses. However, the relationship between them in plant response to stress, especially heavy stress, is largely unclear. This study demonstrated that both AsA and NO could enhance the tolerance of wheat seedlings to cadmium stress evidenced by root length change, which resulted from their roles in maintaining the balance in reactive oxygen species (ROS) and reducing the absorption of Cd. Furthermore, exogenous AsA led to a significant increase of NO content and endogenous AsA content in wheat roots, which could be weakened by the NO scavenger c-PTIO. In addition, c-PTIO also inhibits the NO-induced production of endogenous AsA. Although the AsA synthesis inhibitor lycorine significantly inhibited the inductive effect of exogenous AsA on endogenous AsA production, it has little effect on NO content. In addition, we found that the protective effects of NO and AsA on Cd stress were removed by c-PTIO and lycorine. These results indicated that NO accumulation could be necessary for exogenous AsA-induced cadmium tolerance and endogenous AsA production, and the exogenous AsA-induced endogenous AsA production was likely mediated by NO signaling pathways and together they induced the tolerance of wheat to cadmium stress.