The role of reactive oxygen species and nitric oxide in the formation of root cortical aerenchyma under cadmium contamination

The present study aimed to evaluate root cortical aerenchyma formation in response to Cd‐driven hydrogen peroxide (H2O2) production and the role of nitric oxide (NO) in the alleviation of Cd oxidative stress in maize roots and its effects on aerenchyma development. Maize plants were subjected to continuous flooding for 30 days, and the following treatments were applied weekly: Cd(NO3)2 at 0, 10, and 50 μM and Na2[Fe(CN)5NO]·2H2O (an NO donor) at 0.5, 0.1, and 0.2 μM. The root biometrics; oxidative stress indicators H2O2 and malondialdehyde (MDA); and activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were analyzed. The root dry and fresh masses decreased at higher concentrations of NO and Cd. H2O2 also decreased at higher NO concentrations; however, MDA increased only at higher Cd levels. SOD activity decreased at higher concentrations of NO, but CAT activity increased. Aerenchyma development decreased in response to NO. Consequently, NO acts as an antagonist to Cd, decreasing the concentration of H2O2 by reducing SOD activity and increasing CAT activity. Although H2O2 is directly linked to aerenchyma formation, increased H2O2 concentrations are necessary for root cortical aerenchyma development.