Water Stress Induces the Up-regulation of a Specific Set of Genes in Plants: Aldehyde Dehydrogenases as an Example

The deleterious effect of osmotic stress is often caused by the accumulation of reactive molecules e.g. aldehydes. These molecules can cause lipid peroxidation and modifications of proteins and nucleic acids. Aldehydes can be converted to non-toxic carboxylic acids by different aldehyde dehydrogenases (ALDH). ALDHs occur in all organisms implicating their importance in general biological functions. Aldehydes do not only represent toxic molecules but they are also intermediate products in the synthesis of osmolytes which have been shown to be protective molecules in osmotic stress. For this reason a careful balance of aldehydes is required. Evidence emerges that ALDH enzymes are involved in maintaining this balance, and the investigation of the physiological role of plant-ALDHs begins to attract attention. This review tries to summarize the current knowledge of stressregulated ALDHs in plants. It describes how ALDHs can be used to obtain more stress tolerant plants by overexpressing ALDH genes. ALDH genes have been used in two ways: 1. to obtain increased accumulation of osmolytes e.g. glycine betaine, 2. to detoxify aldehydes.