Cool season crops face intermittent drought. Exposure to drought and other abiotic stresses is known to increase tolerance of the plants against subsequent exposure to such stresses. Storage of environmental signals is also proposed. Preexposure to a dehydration shock improved adaptive response during subsequent dehydration treatment in a cool season crop chickpea (Cicer arietinum). We have identified 101 dehydration-inducible transcripts of chickpea by repetitive rounds of cDNA subtraction; differential DNA-array hybridization followed by northern-blot analysis and analyzed their responses to exogenous application of abscisic acid (ABA). Steady-state expression levels of the dehydration-induced transcripts were monitored during the recovery period between 2 consecutive dehydration stresses. Seven of them maintained more than 3-fold of expression after 24 h and more than 2-fold of expression level even at 72 h after the removal of stress. Noticeably, all of them were inducible by exogenous ABA treatment. When the seedlings were subjected to recover similarly after an exposure to exogenous ABA, the steady-state abundances of 6 of them followed totally different kinetics returning to basal level expression within 24 h. This observation indicated a correlation between the longer period of abundance of those transcripts in the recovery period and improved adaptation of the plants to subsequent dehydration stress and suggested that both ABA-dependent and -independent mechanisms are involved in the maintenance of the messages from the previous stress experience.Plants are often exposed to various environmental stresses when grown in field and within a physiological tolerance limit. A mild abiotic stress induces an adaptive response in the plant, allowing it to grow with a greater tolerance to the same or different stresses (Siminovitch and Cloutier, 1982;Lang et al., 1994;Mantyla et al., 1995;Knight et al., 1998). Pretreatment with thermal or chemical shock induced a substantial chilling tolerance in germinated cucumber seeds (Jennings and Saltveit, 1994). Wilted excised cabbage leaves recovered turgor in absence of water uptake when allowed to lose water at a slow rate (Levitt, 1986). Plants express a number of genes in response to water deficit. At the cellular level, a part of this response results from cell damage, whereas the others correspond to adaptive processes. Adaptation to water deficit brings about changes in the metabolic processes and perhaps in the structure of the cell that allows the cells to continue metabolism at low water potential (Ingram and Bartels, 1996). Dehydration and other stresses cause rapid elevation in the cytosolic free calcium ion ([Ca 12 ] cyt ) concentration (Knight et al., 1991). As an adaptive response, the subsequent stresses show altered magnitude and kinetics of [Ca 12 ] cyt , depending on the nature and intensity of the previous stress even after a 48-h deacclimation period, indicating existence of a signal storage mechanism. Different stress-exposure alters cytosolic ...

The responses of seedlings of three fast growing tree species, Eucalyptus hybrid (E. camaldulensis x E. teriticornis), Casuarina equisetifolia and Melia azedarach, to different levels of soil moisture in controlled glasshouse conditions were compared. The survival percentage, height of plants, number of leaves per plant, number of branches, fresh mass and dry mass of roots, stems, branches and leaves decreased in the three species with increasing water stress. Stomatal frequency and length of stomata in Eucalyptus and Melia also decreased with increasing water stress. However, no significant difference was obtained in the width of stomata and the ratio of number of open stomata to total number of stomata per unit area. The leaf thickness decreased, but the thickness of palisade parenchyma increased with increasing water stress in Eucalyptus hybrid and Casuarina. Leaf thickness of Melia did not show any significant variation due to water stress.