Journal of Integrative Plant Biology 2006, 48 (3): 249-254 Received 16 Jul. 2005 Accepted 10 Oct. 2005 Supported by the Grant to Innovative Young Scholars of Jiangsu Province in China (BK2004417) and by Student Research Training (SRT) Project (0506A03, 0512A11, and 0506B03) of Nanjing Agricultural University. *Author for correspondence. Tel (Fax): +86 (0)25 8439 6673; E-mail: <wbshenh@njau.edu.cn>. www.blackwell-synergy.com; www.chineseplantscience.com Carbon Monoxide Alleviates Salt-Induced Oxidative Damage in Wheat Seedling Leaves Ben-Kai Huang 1 , Sheng Xu 1 , Wei Xuan 1 , Ming Li 2 , Ze-Yu Cao 1 , Kai-Li Liu 1 , Teng-Fang Ling 1 and Wen-Biao Shen 1 * (1. College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China; 2. College of Sciences, Nanjing Agricultural University, Nanjing 210095, China) Abstract Carbon monoxide (CO), a by-product released during the degradation of heme by heme oxygenases (EC 1.14.99.3) in animals, is regarded as an important physiological messenger or bioactive molecule involved in many biologi- cal events that has been recently reported as playing a major role in mediating the cytoprotection against oxidant-induced lung injury. In the present study, we first determined the protective effect of exogenous CO against salt-induced oxidative damage in wheat seedling leaves. Wheat seedlings treated with 0.01 μmol/L hematin as the CO donor demonstrated significant reversal of chlorophyll decay, dry weight, and water loss induced by 300 mmol/L NaCl stress. Interestingly, the increase in lipid peroxidation observed in salt-treated leaves was reversed by 0.01 μmol/L hematin treatment. Time-course analyses showed that application of 0.01 μmol/L hematin enhanced guaiacol peroxidase, superoxide dismutase, ascorbate peroxidase and catalase activities in wheat seedling leaves subjected to salt stress. These effects are specific for CO because the CO scavenger hemoglobin (1.2 mg/L) blocked the actions of the CO donor hematin. However, higher concentration of the CO donor (1.0 μmol/L) did not alleviate dry weight and water loss of salt-stressed wheat seedlings. These results suggest that exogenous application of low levels of a CO donor may be advantageous against salinity toxicity. Key words: carbon monoxide; lipid peroxidation; oxidative stress; salinity; seedling leaves; wheat. Huang BK, Xu S, Xuan W, Li M, Cao ZY, Liu KL, Ling TF, Shen WB (2006). Carbon monoxide alleviates salt-induced oxidative damage in wheat seedling leaves. J Integrat Plant Biol 48(3), 249-254. A variety of abiotic stresses, including salinity, drought, chilling, heat shock, UV irradiation, and heavy metals, often cause diverse molecular oxidative damage to plants, either directly or indirectly through the overproduction of reactive oxygen species (ROS; Allen 1995; Mittler 2002). In response to these abiotic stresses, plants have evolved a complex anti-oxidant system to avoid the harmful effects of ROS. For example, major ROS-scavenging mechanisms of plants include guaiacol peroxidase (POD), super- oxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX; Egley et al. 1983; Mittler 2002). It is well known that salt stress is a key factor that reduces crop production in agriculture (Zhu 2001). Normally, salinity inhib- its growth and reduces the yield of many plant species. It is com- monly hypothesized that plant growth inhibition under conditions of salt stress is partially associated with osmotic effects. Associ- ated with these osmotic effects, a reduction in chloroplast stro- mal volume and the generation of ROS are thought to play impor- tant roles in inhibiting photosynthesis (Price and Hendry 1991). Furthermore, overproduction of ROS caused by salinity usually leads to lipid peroxidation and severe impairment of seedling sur- vival (Mittler 2002). Carbon monoxide (CO) is an odorless, tasteless, and colorless gas generated by heme oxygenase enzymes (HOs; EC 1.14.99.3). The HOs degrade heme molecules, releasing equimolar amounts of CO, iron, and biliverdin (BV), which is subsequently reduced to bilirubin (Verma et al. 1993; Lamar et al. 1996; Longo et al. 1999; . Rapid Communication .