Apoptotic Cell Death in Plants: The Role of Ethylene

Abstract

Programmed cell death (PCD) applies to cell death that is a normal part of the life of a multicellular organism; it results in controlled disassembly of the cell. In animal systems, PCD is synonymous with apoptosis, a cell death process characterized by a distinct set of morphological and biochemical features and breakdown of DNA at internucleosomal sites resulting in a DNA-ladder pattern on agarose gels. These typical changes are thought to be mediated by a class of specific cysteine proteases called caspases. Although numerous processes in plants conform to the general definition of PCD there is no a priori reason that a relationship exists with the caspase-mediated cell death process in animal cells that is commonly called PCD or apoptosis. Treatment of tomato suspension cells with chemicals known to induce apoptosis in animal systems induced cell death. This chemical-induced cell death was accompanied by development of morphological features typical for animal apoptosis and DNA laddering indicating that apoptotic cell death was induced. Treatment of the cells with ethylene or 1-aminocyclopropane-1-carboxylic acid (ACC) greatly stimulated, while inhibitors of ethylene biosynthesis or action effectively blocked chemical-induced cell death. These results indicate that ethylene is a mediater of apoptotic cell death in plants.