Expression of the Tobacco Non-symbiotic Class 1 Hemoglobin Gene Hb1 Reduces Cadmium Levels by Modulating Cd Transporter Expression Through Decreasing Nitric Oxide and ROS Level in .

Hemoglobin (Hb) proteins are ubiquitous in plants, and non-symbiotic class 1 hemoglobin (Hb1) is involved in various biotic and abiotic stress responses. Here, the expression of the tobacco () hemoglobin gene in () showed higher cadmium (Cd) tolerance and lower accumulations of Cd, nitric oxide (NO), and reactive oxygen species (ROS) like hydrogen peroxide (HO). -expressing exhibited a reduced induction of NO levels in response to Cd, suggesting scavenging of NO by Hb1. In addition, transgenic plants had reduced accumulation of ROS and increased activities of antioxidative enzymes (catalase, superoxide dismutase, and glutathione reductase) in response to Cd. While the expression of the Cd exporters ABC transporter (PDR8) and Ca/H exchangers () was increased, that of the Cd importers iron responsive transporter 1 () and P-type 2B Ca ATPase () was reduced in response to Cd. When Col-0 plants were treated with the NO donor sodium nitroprusside (SNP) and HO, the expression pattern of Cd transporters (, , , and ) was reversed, suggesting that expression decreased the Cd level by regulating the expression of Cd transporters via decreased NO and ROS. Correspondingly, -expressing showed increased Cd export. In summary, the expression of reduces Cd levels by regulating Cd transporter expression via decreased NO and ROS levels in .