Nitric oxide acts as an antioxidant and inhibits programmed cell death induced by aluminum in the root tips of peanut ( Arachis hypogaea L.)

Aluminum (Al) causes programmed cell death (PCD) in plants. Our previous studies have confirmed that nitric oxide (NO) inhibits Al-induced PCD in the root tips of peanut. However, the mechanism by which NO inhibits Al-induced PCD is unclear. Here the effects of NO on mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA), activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), expression of alternative oxidase ( AhAOX ) and cytochrome oxidase ( AhCOX ) were investigated in peanut ( Arachis hypogaea L.) root tips treated with Al. The results showed that Al stress induced rapid accumulation of H 2 O 2 and MDA and increased the ratio of SOD/APX. The up-regulation of AhAOX and AhCOX expressions was not enough to inhibit PCD occurrence. Sodium nitroprusside (SNP, a NO donor) decreased the ratio of SOD/APX and eliminated excess H 2 O 2 and MDA, thereby inhibiting Al-induced PCD in the root tips of peanut. The expression of AhAOX and AhCOX was significantly enhanced in Al-induced PCD treated with SNP. But cPTIO (a NO specific scavenger) supply had the opposite effect. Taken together, these results suggested that lipid peroxidation induced by higher levels of H 2 O 2 was an important cause of Al-induced PCD. NO-mediated inhibition of Al-induced PCD was related to a significant elimination of H 2 O 2 accumulation by decreasing the ratio of SOD/APX and up-regulating the expression of AhAOX and AhCOX .