Gene Expression and Signal Transduction in Water-Stress Response

Land plants suffer from dehydration or water stress not only under drought and high-salt-concentration conditions but also under low-temperature conditions. They respond and adapt to water stress to survive these environmental stress conditions. Water stress induces various biochemical and physiological responses in plants. Under water-stress conditions plant cells lose water and decrease turgor pres- sure. The plant hormone ABA increases as a result of water stress, and ABA has important roles in the tolerance of plants to drought, high salinity, and cold. A number of genes that respond to drought, salt, and cold stress at the transcriptional level have recently been described (for re- view, see Ingram and Bartels, 1996; Shinozaki and Yamaguchi-Shinozaki, 1996; Bray, 1997). The mRNAs of water-stress-inducible genes decrease when the plants are released from stress conditions, which is consistent with evidence that shows that these genes respond to water stress or dehydration. The functions of some gene products have been predicted from sequence homology with known proteins and are thought to have a role in protecting the cells from water deficit (Ingram and Bartels, 1996; Bray,