Drought-induced responses in plant cells.

Plants subjected to water stress undergo numerous physiological and metabolic changes. A general decrease in photosynthetic rate is among the most common responses. This is due to a programmed process involving the closure of stomata and reduction in the activity of photosynthetic enzymes. The plant hormone abscisic acid plays an important role in this process. Accumulation of compatible solutes, during water stress, is thought to be an adaptive response which has been developed by some plant species. Engineering the genes involved in the synthesis of these compounds, into nonaccumulating plants, has demonstrated promising results for genetic improvement of drought tolerance. Drought stress induces alteration of gene expression. A large number of genes which are upregulated by water stress have been isolated and characterized. Proteins encoded by some of these genes share several characteristics. The biochemical role of most of these gene products is unknown, but potential adaptive functions have been suggested. Abscisic acid is involved in the regulation of some of these genes.