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 i s an important event, since the location of ACC oxidase determines the site s of ethylene release and action. Whether or not a target gene will be affe cted by ethylene depends on the availability of a free ethylene sensor and a functional signal transduction chain in the cell. In tomato plants, the g ene encoding for the eTAE1 protein is constitutively expressed; if the rece ptor is free, ethylene binds to it and initiates a kinase cascade. If no re ceptor 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 amel iorate the effects of ethylene. (C) 2001 Editions scientifiques et medicale s Elsevier SAS.