Ethylene and flooding stress in plants

The compartmentalization of enzymes involved in ethylene synthesis plays an important role in a plant's response to flooding. Accelerated synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) takes place in roots following the induction of ACC synthase genes by hypoxia. ACC is transported in the xylem to the shoots. Early induction of ACC oxidase by ethylene in shoots is an important event, since the location of ACC oxidase determines the sites of ethylene release and action. Whether or not a target gene will be affected by ethylene depends on the availability of a free ethylene sensor and a functional signal transduction chain in the cell. In tomato plants, the gene encoding for the eTAE1 protein is constitutively expressed; if the receptor is free, ethylene binds to it and initiates a kinase cascade. If no receptor is available, ethylene either dissolves in lipids or diffuses away. The concentration of endogenous ethylene trapped inside a plant depends on the plant's physiological status and environmental conditions. Inhibitors, gene suppression, heterologous gene expression, and plant growth promoting bacteria that contain ACC deaminase activity have all been employed to ameliorate the effects of ethylene. (C) 2001 Editions scientifiques et medicales Elsevier SAS.