Abstract: Carbon monoxide (CO), an endogenous signaling molecule in animals, also provides potent cytoprotective effects including attenuation of lung lipid peroxidation induced by oxidant in the mouse. Our recent work demonstrated that 0.01 mmol/L hematin (a CO donor) treatment of wheat plants alleviated salt-induced oxidative damage in seedling leaves. In this report, we further discovered that hematin pretreatment ( 0.1 mmol/L) could delay wheat leaf chlorophyll loss mediated by further treatment of H2O2 and paraquat, two reactive oxygen species (ROS) sources, in dose- and even time-dependent manners. Also, compared with the control samples, seedling leaves pretreated with 0.01 or 0.1 mmol/L hematin for 24 h exhibited lower levels of H2O2 and lipid peroxidation, as well as higher contents of chlorophyll and activities of antioxidant enzymes. Such beneficial effects exerted by hematin were mimicked by the pretreatment of antioxidant butylated hydroxytoluene (BHT), and differentially reversed when CO scavenger hemoglobin (Hb), or CO specific synthetic inhibitor ZnPPIX was added, respectively. Taken together, the results presented in this paper directly illustrate for the first time that CO is able to strongly protect plants from oxidative damage caused by the overproduction of ROS, and strengthens the evidence that CO is a potent antioxidant in various abiotic and biotic stresses, as similar results have been shown in animal tissues.

Key words: antioxidant, carbon monoxide, chlorophyll loss, hydrogen peroxide, oxidative stress, paraquat, wheat.