To identify genes of potential importance to cold, salt, and drought tolerance, global expression profiling was performed on Arabidopsis plants subjected to stress treatments of 4°C, 100 mm NaCl, or 200 mm mannitol, respectively. RNA samples were collected separately from leaves and roots after 3-and 27-h stress treatments. Profiling was conducted with a GeneChip microarray with probe sets for approximately 8,100 genes. Combined results from all three stresses identified 2,409 genes with a greater than 2-fold change over control. This suggests that about 30% of the transcriptome is sensitive to regulation by common stress conditions. The majority of changes were stimulus specific. At the 3-h time point, less than 5% (118 genes) of the changes were observed as shared by all three stress responses. By 27 h, the number of shared responses was reduced more than 10-fold (Ͻ 0.5%), consistent with a progression toward more stimulus-specific responses. Roots and leaves displayed very different changes. For example, less than 14% of the cold-specific changes were shared between root and leaves at both 3 and 27 h. The gene with the largest induction under all three stress treatments was At5g52310 (LTI/COR78), with induction levels in roots greater than 250-fold for cold, 40-fold for mannitol, and 57-fold for NaCl. A stress response was observed for 306 (68%) of the known circadian controlled genes, supporting the hypothesis that an important function of the circadian clock is to "anticipate" predictable stresses such as cold nights. Although these results identify hundreds of potentially important transcriptome changes, the biochemical functions of many stress-regulated genes remain unknown.Plants have a remarkable ability to cope with highly variable environmental stresses, including cold, drought, and soils with changing salt and nutrient concentrations (i.e. abiotic stress). Nevertheless, these stresses together represent the primary cause of crop loss worldwide (Boyer, 1982), reducing average yields for most major crop plants by more than 50% (Bray et al., 2000). In contrast, the estimated yield loss caused by pathogens is typically around 10% to 20%.Significant progress has been made to understand and manipulate abiotic stress responses (for reviews, see Shinozaki and Yamaguchi-Shinozaki, 1996;Bohnert and Sheveleva, 1998;Smirnoff, 1998;Blumwald, 2000;Bray et al., 2000;Cushman and Bohnert, 2000;Hasegawa et al., 2000;Knight, 2000;Schroeder et al., 2001;Serrano and Rodriguez-Navarro, 2001;Thomashow, 2001;Zhu, 2001bZhu, , 2001a. Three important themes have emerged.First, the initiation of most stress treatments correlates with a cytosolic calcium release, in some cases with stimulus-specific patterns of oscillation (Allen et al., 2000;Knight, 2000;Posas et al., 2000). Second, stimulus-specific changes in gene expression are often observed alongside a set of shared stress responses. For example, in a survey of 1,300 Arabidopsis genes, the majority of cold and drought stressregulated genes were observed as a shared stress ...

Previous work on the adaptation of maize (Zea mays) primary roots to water deficit showed that cell elongation is maintained preferentially toward the apex, and that this response involves modification of cell wall extension properties. To gain a comprehensive understanding of how cell wall protein (CWP) composition changes in association with the differential growth responses to water deficit in different regions of the elongation zone, a proteomics approach was used to examine water soluble and loosely ionically bound CWPs. The results revealed major and predominantly region-specific changes in protein profiles between well-watered and water-stressed roots. In total, 152 water deficit-responsive proteins were identified and categorized into five groups based on their potential function in the cell wall: reactive oxygen species (ROS) metabolism, defense and detoxification, hydrolases, carbohydrate metabolism, and other/unknown. The results indicate that stress-induced changes in CWPs involve multiple processes that are likely to regulate the response of cell elongation. In particular, the changes in protein abundance related to ROS metabolism predicted an increase in apoplastic ROS production in the apical region of the elongation zone of water-stressed roots. This was verified by quantification of hydrogen peroxide content in extracted apoplastic fluid and by in situ imaging of apoplastic ROS levels. This response could contribute directly to the enhancement of wall loosening in this region. This large-scale proteomic analysis provides novel insights into the complexity of mechanisms that regulate root growth under water deficit conditions and highlights the spatial differences in CWP composition in the root elongation zone.Roots often continue to grow under water deficits that completely inhibit shoot and leaf elongation (Sharp and Davies, 1979;Westgate and Boyer, 1985), and this is considered an important mechanism of plant adaptation to water-limited conditions (Sharp and Davies, 1989). Investigation of the mechanisms of root growth adaptation to water deficit is important for improving plant performance under drought, because water resources for agriculture are becoming increasingly limited.The physiology of maize (Zea mays) primary root elongation at low water potentials has been studied extensively (for review, see Sharp et al., 2004), which has provided the foundation for an understanding of the complex network of responses involved. Analysis of the relative elongation rate profile within the root elongation zone showed that under severe water deficit, elongation rates are fully maintained in the apical few millimeters but progressively inhibited as cells are displaced further from the root apex (Sharp et al., 1988;Liang et al., 1997). To help understand the maintenance of elongation in the apical region of roots growing under water deficit conditions, Spollen and Sharp (1991) measured the spatial distribution of turgor pressure and found that values were uniformly decreased by over 50% throughout the e...