Secretion mechanisms of volatile organic compounds in specialized cells of aromatic plants

The present review focuses on cells secreting volatile odorant compounds. This cell type is found in a wide variety of plants, grouped under the term aromatic plants. Such secreting cells are very diverse in morphology, from highly specialized trichomes to nonspecialized cells, including the secretory epidermal cells of petals and osmophores. In these various types of cell, the biosynthetic pathways of three main groups of volatile organic compounds are recognized: isoprenoids, fatty acid derivatives and aromatic compounds. The precise cellular localization of these pathways has not yet been elucidated in all cases, though many of the enzymes involved have already been cloned. These have been found to be frequently located in plastids but also in endoplasmic reticulum or even cytosol. Two alternative mechanisms of secretion termed granulocrine and eccrine have been postulated to exist. Recent studies support the fact that both mechanisms could exist for different compounds and different plants. This review will discuss also the route by which secreted molecules make their way through the cell wall and cuticle