Role of Nitric Oxide in Programmed Cell Death

In recent years, nitric oxide has emerged as a key signaling molecule in plants. This small water- and lipid-soluble gas is involved in several biological processes including stomatal closure, seed germination, root development, and programmed cell death. Nitric oxide, together with reactive oxygen species and salicylic acid, plays a pivotal role in defense strategies against pathogen attack, such as the hypersensitive response and systemic acquired resistance. The cross talk among NO, ROS, and SA is not yet clear, with these molecules interacting at multiple levels, from their biosynthesis to signaling. Because NO is involved in many types of PCD, such as that resulting from both biotic and abiotic stress, it has been proposed as a general stress molecule. In this chapter, the role of NO in cadmium-induced PCD will be discussed, suggesting a possible regulatory role in response to heavy metal stress.