Programmed cell death (PCD) research in higher plants has blossomed in the past ten years. Many evidences suggested that reactive oxygen species,ethylene, Ca2+, salicylic acid, nitric oxide etc. are important signal molecules during environmental stress-induced PCD in plants. Like apoptosis in animals, there also exists a Caspase-dependent PCD signal transduction pathway, in which mitochondrion plays a role of central depot.